Chemistry Segment 2 Study Guide

By: Lexi Pelton

Module 5

Matter exists in 4 phases. Solid, Liquid, Gas, and Plasma.

· Phases: A distinct form of matter in which all chemical and physical properties are identical for a given sample, such as solid, liquid, and gas.

· Solid: State or phase of matter that has a definite shape and volume

· Liquid: State or phase of matter that has an indefinite shape and a definite volume.

· Gas: State or phase of matter that has an indefinite shape and an indefinite volume.

· Plasma: The state or phase of matter in which the electrons have been separated from the atoms, often called ionized gas.

the phase of matter is considered a physical property because a change in a substance’s phase does not change the chemical properties or identity of the substance. The phases of matter are determined by the kinetic energy of the particles and the attractive forces between the particles. Remember that there are attractions between particles, called intermolecular forces. The effects of the motion of the particles on these attractions determines the arrangement of the particles in a sample of matter.

TYPES OF PHASE CHANGES:

· Melting: process of a solid transforming into a liquid when a heat is added kinetic energy increases

· Melting Point: the temperature at which a given substance melts

· Freezing: process of transforming a liquid to a solid by the removal of heat, reverse of the melting process

· Freezing point: the temperature at which a given substance transforms from a liquid to a solid

· Evaporating: Process of turning a liquid to a gas

· Vapor: Means the same thing as evaporation. In fact, the two words are related. The process of becoming a gas can also be called vaporization.

· Boiling: This process occurs when the temp is high enough, evaporation occurs from within the liquid

· Boiling Point: temperature at which a substance boils.

** Boiling point of pure water is 100° C

· Condensing: The opposite of the evaporation process; the process of a gas transforming into a liquid

· Condensation point: temperature at which the phase change condensation occurs.

· Same temp as the substances boiling point.

REVIEW:

Heating and cooling curves ( lesson 05.02)

GAS LAWS:

Physical Characteristics and Variable

Typical Units

Volume (V)

liters (L)

Pressure (P)

Atmospheres (atm)

Temperature (T)

Kelvin (K)

Number of particles (n)

Moles (mol)

Ideal gas constant, R

0.082 L * atm / K mol

You have already seen that scientists use moles, temperature, and volume to measure matter. Another measurement, pressure, is also necessary for describing a sample of gas. Pressure is defined as the force per area on a surface.The SI unit of pressure is the Pascal (Pa), which is defined as one newton per square meter(N/m2).However, chemists most often use units of atmospheres (atm) or millimeters of mercury (mm Hg) to measure pressure. (Millimeters of mercury are also known as torr, in honor of Evangelista Toricelli, the inventor of the mercury barometer.)

Units of Pressure

1 atmosphere (atm)

= 760 mm Hg

= 760 torr

= 101.3 kilopascals (kPa)

When you want to convert from Celsius to Kelvin K= 273.15 + oC

When you want to convert Kelvin to Celsius oC= K-273.15

NATURE OF GASSES:

· Low Density

The density of a substance in the gas phase is about 1/1,000 the density of the same substance as a liquid because the gas particles spread out so much farther from each other than they do as a liquid.

· Compressibility

When enough pressure is applied, gases can be compressed to a smaller volume because there is so much space between the particles. With enough pressure, a gas can sometimes be compressed to a volume thousands of times smaller than its initial volume.

· Expansion

Gases spread out to fill the entire container in which they are enclosed because the gas particles are moving in all directions with negligible attractive forces between them. This means that a gas transferred from a 2-liter container to a 4-liter container will expand, or spread out, to fill the entire 4-liter container.

· Diffusion

Have you ever opened a bottle of cologne or ammonia on one end of the room and somebody nearby commented on the smell just moments later? Because of their high kinetic energy and random motion, gas particles can spread out and mix with each other without being stirred. The scent of ammonia travels through a room as its gas particles mix with the particles of air.

· Fluidity

Gas particles are able to easily glide, or flow, past each other because the attractive forces between them are negligible. The term fluid is sometimes used to describe both liquids and gases because of their ability to flow.

REVIEW THE KINETIC MOLECULAR THEORY OF GASSES (found at the bottom of lesson 05.03)

4 Gas Laws:

1. Gay-Lussac’s Law:

2. Avogadro’s Law

3. Charles’s Law

4. Boyle’s Law

Gas Calculations:

Ideal Gas Law: A model gas that conforms perfectly to all of the assumptions of the kinetic theory:

PV = nRT

R = 0.0821

Standard Temperature and Pressure

To aid in the comparisons of volumes or moles of gases, scientists have agreed upon conditions known as standard temperature and pressure, commonly abbreviated STP. The conditions of standard temperature and pressure are exactly one atmosphere pressure and 0°C (273.15 Kelvin).

Avogadro’s principle states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles. At standard temperature and pressure (STP), one mole of any gas occupies a volume of 22.4 liters. This mole-to-volume relationship can be used as conversion factor in calculations pertaining to measurements and reactions conducted at STP (1 atmosphere and 273.15 Kelvin).

Standard temperature and pressure

(STP)

1 standard temperature

0°C

1 standard temperature

273 K

1 standard pressure

1 atm

1 standard pressure

760 torr

1 standard pressure

14.7 psi

Diffusion: The gradual mixing of two gases because of the spontaneous, random motion of their particles.

Effusion: The movement of gas particles through a small opening in the container wall due to the pressure and particle movement inside the container.

Graham's Law

This equation shows that the rate at which two different gases (A and B) effuse from the same container is dependent on their molar masses. Notice that in the equation the molar mass of A is diagonal from the rate of A. Also notice that to actually calculate and compare the rates of effusion,  the square root of each molar mass must be taken

Graham’s law can be applied in a variety of ways:

All matter can be classified into two categories: pure substances and mixtures.

Mixture: A combination of two or more substances, each retaining its individual composition and properties.

Mixtures vs. Compounds

There is an important difference between the way atoms combine to form compounds and the way particles come together to form mixtures.

When a compound is formed, it has different chemical and physical properties than the pure elements it is made of, and it can only be separated by a chemical change.

In a mixture, the individual substances retain their own properties and can be separated easily by physical means. Refer to the table below to see a comparison of compounds and mixtures

Heterogeneous Mixture: A mixture in which the composition and properties are not uniform throughout the mixture.

Homogeneous Mixture: A mixture in which the composition and properties are uniform, or the same, through-out the mixture.

Separating Mixtures:

1. Filtration

2. Evaporation

3. Simple Distillation

4. Chromatography

Solvent: In a solution, the substance that is in a greater quantity; the dissolving medium.

Solute: In a solution, the substance that is in a lower quantity; the substance being dissolved.

Saturated Solution: A solution containing the maximum amount of solute able to be dissolved under the given conditions

Unsaturated Solution: A solution containing less solute than a saturated solution under the given conditions

Colligative Property: A property of a solvent that depends on the number of solute particles dissolved in it, but not on the identity or nature of those solute particles

Vapor Pressure: The pressure exerted by the vapor particles that evaporate from a liquid (or solid).

Molality: The concentration of a solution in moles of solute per kilogram of solvent.

Molality (m) =

Module 6

Heat: The transfer of thermal energy from one substance to another due to the temperature difference between the two substances

Isolated System:

In an isolated system, neither matter nor energy is permitted to exchange with the surroundings. This means that the total amount of energy and matter contained in an isolated system will remain constant, because energy and matter cannot enter or leave.

Our universe is an example of an isolated system. Scientists theorize that the total amount of matter and energy remain constant within the universe and cannot be exchanged with any surroundings.

There are not many examples of true isolated systems, because it can be difficult to completely block the exchange of energy between a system and its surroundings, but some systems come closer than others. Using insulated containers, such as coolers and foam cups, helps to minimize the amount of heat flow between system and surroundings.

Closed System:

In a closed system, energy can enter or leave the system but matter cannot.

Earth is an example of a closed system. The outer edge of the atmosphere acts as a boundary between the system, Earth, and its surroundings. Matter does not ordinarily enter or leave the system, except for the occasional meteorite or space shuttle, but energy is freely transferred between Earth and its surroundings.

Chemists can use glassware, such as flasks and beakers, to contain matter but allow energy to be exchanged. Light and heat can pass through the glass in either direction, making sealed glass containers another example of a closed system.

Open System:

In an open system, both matter and energy are exchanged freely between the system and the surroundings.

Your body is an example of an open system. Matter and energy both enter and leave your body throughout the day. These exchanges are important to keep your body functioning properly.

When reactions occur in unsealed containers, matter and energy are both able to be exchanged freely between the system and surroundings. When vinegar and baking soda react together in an open container, the gaseous product escapes to the surrounding air as heat flows out of the container.

Thermochemistry: study of the changes in energy that accompany chemical reactions and physical changes.

Endothermic Process: A chemical or physical change that absorbs energy from the surroundings.

Exothermic Process: A chemical or physical change that releases energy to the surroundings.

06.02 Review energy diagrams.

Specific Heat Capacity: The quantity of heat required to raise the temperature of one gram of the substance by one degree Celsius.

J/(°C * g)

The energy gained or lost is called enthalpy which is represented by the letter, q.

q = m × c × Δt

q: The q represents the heat gained or lost by the system, in joules.

m: The m in this equation represents the mass of the sample, measured in grams.

c: The c represents the specific heat capacity of the substance being heated or cooled. The unit for specific heat capacity is joules per gram per degree Celsius.

Δt: Delta t (Δt) represents the change in temperature, in degrees Celsius, when a substance gains or loses energy. The change in temperature can be determined by subtracting the initial temperature from the final temperature of the substance (tf – ti).

Enthalpy Change

The enthalpy change of a system is equal to the energy flow of heat between the system and its surroundings when the pressure remains constant. The symbol for enthalpy is represented by the symbol ΔH.

The sign on the enthalpy change value can be either negative or positive. The sign represents the direction of the heat flow from the perspective of the system, qsystem to the surroundings, qsurroundings.

A negative enthalpy change value means that energy was lost by qsystem to the qsurroundings. This is called an exothermic process.

A positive enthalpy change value means that the energy is absorbed from qsurroundings by qsystem. This is called an endothermic process.

Below is are two interactives that explains this process.

REVIEW 06.04 ENTROPY AND ENTHALPY IN DEPTH

Free Energy

As we have seen, entropy, enthalpy, and temperature all have an effect on the spontaneity of a chemical process. These properties can be combined in an equation that helps determine if a physical or chemical change is spontaneous at a given temperature.

ΔG = ΔH − (T × ΔS)

Collision Theory

Chemists believe that for compounds, atoms, or ions to react successfully, the particles must collide together. This is the basis for a scientific theory known simply as the collision theory.

This theory is based on the idea that the rate of a reaction is determined by the number of successful collisions that occur over a given amount of time. A successful collision is one that results in the making of the product(s).

Two factors—sufficient energy and correct orientation—must be true for a given collision to successfully result in the production of products. Both factors must be true for a given collision for it to go to completion and form the products

Sufficient Energy

The collision between reactants must have enough energy for the reactants’ valence energy levels to penetrate each other. This interaction between valence energy levels allows the electrons to rearrange to form new bonds.

If a collision between two reactants does not have enough energy, the collision will not be able to produce the products.

Energy Distribution

We can use a graph like the one shown to represent the distribution of energy within a sample of particles at a given temperature.

This general curve, called a Maxwell-Boltzmann distribution, shows us that the majority of the particles have moderate amounts of energy, near the average kinetic energy of the sample, while some particles have energy higher or lower than that average value.

Remember that for a reaction to happen particles must collide with energy equal to or greater than the activation energy for the reaction.

That activation energy requirement can be marked on the diagram to show us the amount of a given sample that has the possibility of meeting this energy requirement in a collision.

Correct Orientation

When reactants come in contact with each other during their random movement, the orientation of their collision will determine if the collision is successful. The atoms from each reactant that will bond together to form the new products must come in contact with each other if a bond is going to form between them.

The more complex a reaction is, the slower the rate of the reaction. For example, if more than two reactants need to collide together at the same time with correct orientation the reaction time would be slow.

For the reaction between ethene (CH2CH2) and hydrogen chloride (HCl) to occur, the double bond between the carbon atoms in ethene must be broken.

The double bond is converted to a single bond, allowing the carbon atoms to each bond with one of the atoms from the hydrogen chloride.

REVIEW SLIDES AT THE BOTTOM OF LESSON 06.05

Module 7

When chemists refer to an acid, they are often discussing a compound that donates, or gives off, a hydrogen ion when dissolving in water or reacting with another substance.

There are three commonly accepted chemical definitions of acids, but we will focus on this definition as a hydrogen donor, called the Brønsted-Lowry definition.

Although most acids are molecular compounds, their strong polarity allows the polar water molecules to remove one or more hydrogen ions from the molecule, leaving behind a negative ion.

If the acid is dissolved in water, the positive hydrogen ions bond to water molecules to form hydronium ions (H3O +). In this course, whenever we discuss hydrogen ions in an aqueous solution, we can assume that they will bond with the water molecules to form hydronium ions. This means that the two ions, H+ and H3O+, can be used interchangeably when discussing acidic solutions.

Another common definition of an acid, the Arrhenius definition, describes acids as any substance that increases the hydronium ion concentration of a solution when it is dissolved in water.

Strong Acids

A strong acid is an acid that ionizes close to 100 percent in an aqueous solution. This makes it a strong electrolyte because of the greater concentration of ions in solution, and also means that the concentration of the solution indicates the concentration of hydrogen or hydronium ions in the solution.

Examples:

· Hydrochloric acid:            HCl → H+ + Cl-

· Nitric acid:                        HNO3 → H+ + NO3-

· Sulfuric acid:                    H2SO4 → H+ + HSO4-

· Perchloric acid:                HClO4 → H+ + ClO4-

· Hydrobromic acid:            HBr → H+ + Br-

· Hydroiodic acid:               HI → H+ + I-

Weak Acids

Weak acids vary in their degree of ionization in an aqueous solution, but it is often less than 50 percent. Weak acids are weak electrolytes because there are fewer ions in solution at a given concentration. It is important to remember that a given concentration of a weak acid does not indicate the concentration of hydrogen or hydronium ions in the solution.

Examples:

· Hydrofluoric acid:             HF   H+ + F-

· Phosphoric acid:              H3PO4   H+ + H2PO4-

· Carbonic acid:                  H2CO3   H+ + HCO3-

· Acetic acid:                       CH3COOH   H+ + CH3COO-

· Hydrocyanic acid (Hydrogen cyanide):    HCN   H+ + CN-

Acid Anhydrides

Most acids contain hydrogen ions that break off from the compound when it dissolves in water, as shown in many of the previous examples. However, some acids do not contain hydrogen ions.

These compounds, called acid anhydrides, increase the hydrogen ion concentration of a solution by reacting with water molecules. For example, carbon dioxide does not have any hydrogen in its formula, but it creates carbonic acid when it is dissolved in water. CO2 and H2O react to form the compound H2CO3. Once it is formed, some of the carbonic acid acts as an acid by giving off hydrogen ions to water in the solution.

H2O + CO2 → H2CO3

H2CO3 + H2O   H3O+ + HCO3-

You may not have realized it, but you probably have several substances around your house that would be categorized as bases. Bases are excellent cleaning agents because they react with oils and fats to make them more water-soluble, so you will notice that many of the common bases on our list are found in cleaning products.

Strong Bases

Strong bases ionize close to 100 percent when dissolved in water, while weak bases ionize much less.

Metal hydroxides made from metals of groups one and two in the periodic table are usually considered strong bases.

Examples:

· Sodium hydroxide         NaOH → Na+ + OH-

· Potassium hydroxide     KOH → K+ + OH-

· Lithium hydroxide          LiOH → Li+ + OH-

· Calcium hydroxide         Ca(OH)2 → Ca2+ + 2 OH-

Weak Bases

Examples:

· Ammonia                       NH3 + H2O → NH4+ + OH-

· Pyridine                         C5H5N + H2O → HC5H5N+ + OH-

NaOH + H2O → Na+ + OH− + H2O

When a strong base like sodium hydroxide is dissolved, large amounts of heat are released because the process is exothermic.

READ THROUGH 07.02

Many of the solutions that you encounter every day can be categorized as acidic or basic. Use the pH paper provided to test the pH value of some common substances. Substances with pH values greater than 7 are basic, equal to 7 are neutral, and less than 7 are acidic. Record your findings in your notebook.

In addition to describing a solution as acidic, basic, or neutral, scientists use numerical values to express the acidity of a solution in more detail. Because the concentrations of hydronium and hydroxide ions in a solution can vary greatly, chemists use values called pH to conveniently express a solution’s hydronium ion concentration.

The letters pH stand for the French words pouvoir hydrogène, meaning “hydrogen power.” The pH scale is a numeric scale used to indicate the hydronium ion concentration of a solution. The pH of a solution is determined by calculating the negative base-10 logarithm of the hydronium ion concentration (in molarity).

pH of a Solution

pH= -log

Brackets are used to represent concentration in molarity.

According to the Brønsted-Lowry definition of acids and bases, acids increase the concentration of hydronium ions in a solution by donating hydrogen ions, while bases decrease the concentration of hydronium ions by accepting hydrogen ions. This means that the acidic or basic nature of a substance can both be measured and described by its hydrogen ion, or hydronium ion, concentration. This is why pH values can be used to describe acidic and basic solutions, even though the values are calculated using the concentration of hydronium ions.

The range of pH values of aqueous solutions generally falls between 0 and 14, which is a more reasonable range for comparison than the possible range of concentrations. The pH scale and its values are dependent on temperature, so we will be comparing and calculating pH values at 25 degrees Celsius.

The pH of a neutral solution, when the concentrations of hydroxide and hydronium ions are equal, at 25°C is 7.0. When the amount of hydronium ions is greater than the amount of hydroxide ions in the solution, the solution is acidic and will have a pH value that is lower than 7.0. In a basic solution, the amount of hydroxide ions is greater than the amount of hydronium ions, and the pH will be greater than 7.0.

BASE:

REVIEW SLIDES AT BOTTOM OF LESSON 07.03 IMPORTANT MATH CONCEPTS

Dynamic equilibrium is a state of balance in which the forward and the reverse reactions continue to occur, but the rates of the forward and the reverse reactions are equal. All reactions have the potential to reach equilibrium if they occur in a closed system.

Dynamic equilibrium also occurs when physical changes take place. When water is sealed in a flask, equilibrium will eventually be reached between the evaporation and the condensation processes. The faster-moving molecules in the liquid will escape as vapor, while the slower-moving vapor molecules will condense back into a liquid

Science is based largely on experimental investigations, and the description of equilibrium systems is no different. In 1864, two Norwegian chemists, Cato Guldberg and Peter Waage, used data and observations from numerous reaction systems to propose the law of mass action to describe the equilibrium condition.

Let’s examine the basic concepts of the law of mass action.

Consider the following general reversible reaction. In this example, w moles of A react with x moles of B to produce y moles of C and z moles of D in the forward reaction (w, x, y, and z are coefficients, A and B are reactants in the forward reaction, and C and D are products of the forward reaction).

wA + xB yC + zD

At equilibrium, the concentrations of each substance in the system can be plugged into the equation below. The law of mass action proposes that, for a reaction at a given temperature, this equation can be used to relate the equilibrium concentrations of the substances in the system to the reaction’s equilibrium constant (K).

Remember that brackets are used to represent concentration in molarity (M).

The value of a system's equilibrium constant (K) is constant at a given temperature, regardless of the initial amounts of the reactants and the products introduced into the system. Although there is only one value for the equilibrium constant for a system at a given temperature, there are infinite combinations of equilibrium concentrations of the reactants and the products within the system.

It is important for chemists to understand the factors that can influence the position of a chemical equilibrium. For example, when a chemical is being manufactured, the chemical engineers in charge of production should choose conditions that will result in the greatest amount of products that can be made under reasonable conditions. This means they will choose conditions that move the equilibrium position farther to the right.

We can predict the effects of changes in concentration, temperature, and pressure on a system at equilibrium by using Le Châtelier’s principle

Le Châtelier’s Principle: If a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction that helps to reduce the effect of that change.. This principle, proposed by the French chemist Henri Louis Le Châtelier’s in 1888, states that if a change is imposed on a system at equilibrium, the position of the equilibrium will shift in the direction that tends to reduce the impact of that change. This statement is a simplification of what really happens when a change is imposed on a system, but it works well to help us make qualitative predictions.

There are four possible scenarios that can be produced by a change, or stress, to an equilibrium system:

1. Increasing the rate of the forward reaction will cause the system to shift to the right to reach a new equilibrium.

2. Increasing the rate of the reverse reaction will cause the system to shift to the left to reach a new equilibrium.

3. Decreasing the rate of the forward reaction will cause the system to shift to the left to reach a new equilibrium.

4. Decreasing the rate of the reverse reaction will cause the system to shift to the right to reach a new equilibrium.

REVIEW 07.05

07.06 Oxidation and Reduction: Overview—Text Version

Did you ever wonder what causes copper, like that in pennies and in the Statue of Liberty, to turn green?

This type of reaction involves the exchange of electrons from one substance to another. We have seen that many important compounds are ionic, and ions are atoms that have gained or lost electrons.

Sodium chloride, for example, can be formed by the reaction of sodium metal with chlorine gas:

Na (s) + Cl2 (g) → 2 NaCl (s)

In this reaction, neutral sodium atoms react with neutral, diatomic chlorine molecules to form the ionic compound sodium chloride, which contains Na+ ions and Cl- ions.

Reactions like this one, where one or more electrons are transferred from one particle to another are called oxidation- reduction reactions, or redox reactions for short.

Oxidation

Oxidation is defined as the loss of electrons in a chemical reaction.

In the reaction of sodium and chlorine, neutral sodium was oxidized when it lost an electron to chlorine to make a positive Na+ ion.

This term got its name because many metals lose electrons when they react with oxygen to make an ionic metal oxide compound. Gaining oxygen (after a loss of electrons) is where this term got its name, “oxidized.”

Reduction

Reduction is defined as the gain of electrons in a chemical reaction.

In the reaction above, neutral chlorine got reduced when it gained electrons from the sodium to make a negative Cl- ion.

When an atom or particle gains a negative electron, its overall charge is lowered, or “reduced.” This is where this term comes from.

You Can’t Have One without the Other

Oxidation and reduction go hand in hand. One substance cannot be oxidized unless another substance is reduced.

If one element gains electrons (reduction), it is because another element lost them (oxidation).

An element will not lose electrons (oxidation) unless another element takes them (reduction).

REMINDERS GIVEN IN LESSON:

OIL RIG

Oxidation Is Loss (of electrons)

Reduction Is Gain (of electrons)

LEO the lion says GER

Losing Electrons is Oxidation

Gaining Electrons is Reduction

Rules for Assigning Oxidation Numbers

· Neutral Elements

· Oxygen

· Monatomic Ions

· Covalent Compounds

· Algebraic Sum

Neutral Elements

Neutral elements in their standard state (not in a compound) always have an oxidation number of zero.

Examples (all have an oxidation number of zero):

· O2

· Na

· F2

· S8

· P4

Oxygen

Oxygen always has an oxidation number of -2 when combined with another element, except in peroxides, when it is -1.

Examples:

•H2O (O = -2)

•CaO (O = -2)

•H2O2 (O = -1 because peroxide)

Monatomic Ions

Monatomic ions have an oxidation number equal to their charge as an ion (when alone or when in a compound).

Examples:

NaCl      Na = +1, Cl = -1

· CaBr2    Ca = +2, Br = -1

· Ag+        Ag = +1

· Al3+       Al = +3

Covalent Compounds

For covalent compounds, pretend the compound is ionic with the more electronegative element forming the negative ion (anion). For example: Fluorine is always -1 in a compound, oxygen is almost always -2, and hydrogen is +1 in covalent compounds.

Examples:

· CCl4       C = +4, Cl = -1

· NH3        N = -3, H = +1

Algebraic Sum

The algebraic sum of all the oxidation numbers (multiplied by any subscripts) must add up to the total charge of the compound or ion. This means we can use subtraction to solve for any elements not listed in the previous oxidation number rules.

Covalent Compounds

For covalent compounds, pretend the compound is ionic with the more electronegative element forming the negative ion (anion). For example: Fluorine is always -1 in a compound, oxygen is almost always -2, and hydrogen is +1 in covalent compounds.

Examples:

· CCl4       C = +4, Cl = -1

· NH3        N = -3, H = +1

Algebraic Sum

The algebraic sum of all the oxidation numbers (multiplied by any subscripts) must add up to the total charge of the compound or ion. This means we can use subtraction to solve for any elements not listed in the previous oxidation number rules.

Oxidizing and Reducing Agents

In a redox reaction, one reactant is always an oxidizing agent and another reactant is the reducing agent. It is easy to make a mistake with these terms, so take time to define these terms in your notebook, and to learn and practice these terms.

Agents

Oxidizing Agent: A reactant that causes another substance to be oxidized (not being oxidized itself). The oxidizing agent is the reactant that is reduced.

Reducing Agent: A reactant that causes another substance to be reduced (not being reduced itself). The reducing agent is the reactant that is oxidized.

This may seem backward because the oxidizing agent is being reduced and the reducing agent is being oxidized, but remember that if you are an agent of something, you cause that “something” to happen to someone else. Define all of these terms in your notes and review them because it can be easy to mix them up.

· An oxidizing agent causes another substance to be oxidized.

· The only way to cause oxidation is to remove electrons from that other substance (because oxidation is loss of electrons).

· Therefore, the oxidizing agent is reduced as it gains electrons from the other substance.

Module 8!!!!!!!

Chemical vs. Nuclear Reactions

Atoms are made up of electrons, neutrons, and protons. In the chemical reactions that we have studied throughout this course, the sharing or exchange of electrons was involved in forming bonds and compounds while the neutrons and protons remained unchanged in the nuclei of the atoms.

However, some atoms have unstable nuclei because the number of protons and neutrons are off balance. Atoms with unstable nuclei are radioactive; they eventually break down into a different substance and release energetic particles, or radiation, in the process.

Alpha (α) Radiation

Alpha radiation is made up of a stream of alpha particles. Alpha particles are made up of two protons and two neutrons released from the nucleus of the radioactive atom. This means that alpha particles have a positive charge, and that when an atom releases an alpha particle, its atomic number decreases by two and its mass number decreases by four.

Unstable parent nucleus → resulting daughter nucleus + alpha particle

Alpha particles have a high amount of kinetic energy and can cause damage to surface materials such as skin and living tissue. However, alpha particles are relatively easy to shield against. They cannot normally penetrate lightweight materials such as paper or fabric. Also, as they travel through the air, the particles attract electrons and become neutral helium atoms.

Beta (β) Radiation

Beta radiation is made up of a stream of beta particles. Beta particles are fast-moving electrons released from a nucleus when a neutron breaks apart into one proton and one electron.

Neutron → beta particle (electron) + proton

A negative beta particle, which is a very fast moving electron, is released when a neutron decays. A positive proton is left behind in the nucleus during this type of decay.

When the negative beta particle is released from the nucleus of an atom, the atom ends up with one more proton and one less neutron.

Beta particles have a negative charge and they usually move faster than alpha particles. This means that beta particles are more difficult to protect against than alpha particles; they can penetrate cloth and paper. Beta particles can penetrate deeply into skin and potentially harm or kill living cells. However, these particles cannot penetrate thin layers of denser materials such as aluminum and other metals. When beta particles are finally stopped by a substance, they are absorbed by the material, like any other electron.

Gamma (γ) Radiation

Gamma radiation can be given off during different types of nuclear decay. Gamma rays are a form of electromagnetic waves with a very high frequency and greater energy than ultraviolet light or X-rays.

· Ultraviolet 10-6

· X-ray 10-8

· Gamma Ray 10-10 to 10-12

Because gamma rays have high energy and no mass or charge, they can penetrate through most materials. Gamma rays can cause much more damage to living cells than alpha or beta particles. Only very dense materials, such as thick layers of lead, can stop gamma rays. This is why lead is commonly used as a shielding material in laboratories and hospitals where gamma radiation is present.

Overview

Alpha (α)

Beta (β)

Gamma (γ)

Made up of two protons and two neutrons bound together.

Made up of electrons.

High-frequency photons with no charge.

Move slowly and can be stopped by a sheet of paper or human skin.

Move faster than alpha but lose their energy when they collide with other atoms.

Can penetrate paper and aluminum, but are stopped by a thick layer of lead or concrete (think of wearing lead vests when getting x-rays).

 

Some beta particles can be stopped by human skin, but if they are ingested, the particles can be absorbed into the bones and cause damage.

If a person is exposed to gamma rays, severe damage to their internal organs can occur.

Radioactive Decay

When a radioactive element’s nucleus decays and gives off an alpha or beta particle, the number of protons and neutrons inside the nucleus changes. When this happens, the atom becomes another element. This is what makes nuclear reactions different than regular chemical reactions. In a nuclear reaction, the identities of the elements actually change, because protons and neutrons are gained or lost by the atom over the course of the reaction.

REVIEW THE FOLLOWING CONCEPT OF HALF-LIFE EXTENSIVELY!!!!!! MAKE SURE YOU REALLY KNOW HOW TO DO THIS!!!

Half-Life

Radioactive isotopes decay at different rates, but the rates are all measured in terms of the substance’s half-life. Half-life is the time needed for half of the radioactive atoms in a sample to decay. The half-life of a given isotope is constant and is independent of external conditions or the amount of atoms in the sample. This means that the half-life of a specific isotope will be the same whether you have one million moles or one mole of the atoms.

Radium-226 has a half-life of 1,620 years, which means that half of a given sample of radium-226 will decay into lead by the end of 1,620 years. In the next 1,620 years, half of the remaining sample will decay into lead, leaving one-fourth of the original amount of radium-226.

The half-lives of radioactive substances range from less than a millionth of a second to more than a billion years. Uranium-238 has a half-life of 4.5 billion years! So how can scientists measure half-lives that are that long? The answer is that they do not measure the actual half-life, but they can accurately measure the rate of the isotope’s decay using a radiation detector. The faster a substance decays, the more radiation per minute is detected, and the shorter the half-life of a given isotope. It is not necessary to wait through an entire half-life of a substance; the half-life can be calculated using the rate of decay that is observed.

Once we know the half-life of a substance, this information can be used to estimate the age of ancient remains. One of the most common examples of this is the use of carbon-14 dating to estimate the age of dead organisms or artifacts made of wood or cloth.

REVIEW 08.01 HALF-LIFE PRACTICE QUESTIONS

We know that the particles inside an atom’s nucleus are held together by a strong nuclear force. If a large nucleus is split apart, large amounts of energy can be released. In nuclear fission

Fission: A nuclear reaction in which an atomic nucleus splits into fragments, usually two fragments of comparable mass, with the release of large amounts of energy in the form of heat and radiation., certain heavy elements, such as some forms of uranium, are split when they are struck by a moving neutron.

When an atom of uranium-235 is struck by a moving neutron, the atom’s nucleus absorbs a neutron and becomes unstable. Instead of giving off an alpha or beta particle, like in the other nuclear reactions that we have studied, the heavy uranium isotope splits into two or more smaller, medium-weight atoms.

As the nucleus splits, some free-moving neutrons are released and can collide with more uranium-235 atoms to cause additional fission reactions to occur. When the material or substance that starts a reaction, in this case a neutron, is also produced by the reaction and is available to start another reaction, the process is called a chain reaction

Chain Reaction: A series of reactions in which the material or substance that starts a reaction is also produced by the reaction and is available to start another reaction.. This chain reaction will continue to occur until all of the uranium-235 isotopes have split, or until the neutrons fail to collide with any more uranium-235 nuclei.

The fission of uranium-235 nuclei produces large amounts of energy, estimated to be about seven million times that of the explosion of a TNT molecule. This release of energy is what makes nuclear fission useful as an energy source for communities, but it also comes with possible risks and safety concerns. Most of the energy released by nuclear fission is in the kinetic energy of the fission fragments, the smaller atoms produced when the larger atoms splits, and some of the energy is released as gamma radiation.

Nuclear Power Plants

The magnitude of the power of nuclear fission was introduced to the world in the form of nuclear bombs, which can influence our thinking about nuclear power. Although a similar chain reaction is used in the nuclear fission that occurs in nuclear power plants, the engineering and containment of the reaction is quite different from that of a fission bomb.

According to the U.S. Energy Information Administration, nuclear power plants contributed to 20.3 percent of the electrical power supplied in the United States from June 2009 to May 2010. Coal-fired power plants contributed 46.3 percent and natural gas-fired plants contributed to 21.2 percent of the electrical power in the United States over the same time period. Some countries depend more on nuclear power than the United States. The World Nuclear Association reports that France derives over 75 percent of its electricity from nuclear power, Armenia over 45 percent, and Belgium over 51 percent.

Nuclear power plants, like power plants that use fossil fuels, boil water to produce steam that turns a large turbine. In a nuclear power plant, a kilogram of uranium, about the size of a baseball, produces more steam, and therefore more electricity, than 30 freight-car loads of coal.

Also, fission reactions do not produce the atmospheric pollutants and greenhouse gases that are associated with the combustion of fossil fuels. However, there are risks and by-products associated with a nuclear fission that are different than those associated with the use of fossil fuels. By understanding more about nuclear reactions and power plants, we can each make a more informed decision if someone proposes the construction of a nuclear power plant in our community.

Nuclear Fusion

Nuclear fusion is very different than nuclear fission, but it still involves large amounts of energy released as the nucleus of an atom changes. In nuclear fusion

Fusion: A nuclear reaction in which the nuclei of two very small atoms, such as two hydrogen isotopes, combine together into one larger nucleus., the nuclei of two very small atoms, such as two hydrogen isotopes, combine together into one larger nucleus. Do not confuse this with a regular chemical reaction, where atoms combine by sharing electrons. In nuclear fusion, it is the actual nuclei that combine together to form one new atom, not the combination or exchange of electrons to form a new compound.

The nuclear-fusion reaction below is one proposed by scientists to someday be used in fusion reactors. In this reaction, two different isotopes of hydrogen, deuterium and tritium, fuse together to form one atom of helium, one neutron, and a very large amount of energy.

REVIEW RENEWABLE AND NON RENEWABLE RESOURCES

These are really easy to remember as we have been learning them since 3rd grade :) but it never hurts to refresh your memory!

REVIEW 08.04

It’s just about pollution and its effects on both humans and the environment

Carbon Chemistry

Carbon atoms have the unique ability to bond with other carbon atoms in long chains, rings, and other formations. This property allows carbon to be the base of a variety of large molecules. Have you ever heard the term “carbon-based life-form”? All humans are carbon-based organisms, as are all animals and plants, because we are made up of many different carbon compounds. Life is actually based on carbon’s ability to form diverse molecular structures. There is a branch of chemistry, called organic chemistry, dedicated to the study of compounds that contain carbon.

Because organic compounds are the basis for living organisms and are also used for a variety of applications, such as fuels, medicines, agriculture, flavoring, and more, it is important to have a basic understanding of them. In this lesson, we will discuss the carbon atom and some categories of organic compounds that can be formed because of the unique properties of carbon.

Carbon

Carbon is a nonmetal that is found in nature as both a pure element and in various compounds. It is the 17th-most abundant element, by mass, found on Earth, but it is one of the most important elements to humans because it is found in all living matter.

A carbon atom has four valence electrons in its outermost energy level , and it has a strong tendency to share electrons to have a full octet in its valence. Carbon atoms often naturally bond with each other in chains, rings, plates, or networks, and they also bond readily with hydrogen, oxygen, nitrogen, sulfur, phosphorus, and the halogens.

Carbon occurs in two pure forms, diamond and graphite. These two forms of carbon have very different properties due to the difference in how the carbon atoms are covalently bonded together.

Diamonds are the hardest material known to man. This solid form of carbon is colorless with an extremely high density of 3.514 g/cm3. In a diamond, the carbon atoms are held together by all single bonds formed in a three-dimensional tetrahedral formation. This formation holds the carbon atoms together in a strong and compact structure that makes diamonds so strong and dense.

Graphite is a soft, black, solid form of carbon that conducts electricity reasonably well and is easily broken. The "lead" in your pencil is actually graphite, so you can examine its properties for yourself. The carbon atoms in graphite are arranged in layers of thin hexagonal “plates.” This configuration of carbon atoms is due to the fact that each carbon atom has one double bond and two single bonds, forming a trigonal planar shape of bonds around each carbon atom. The layers of carbon atoms in graphite are only held together by the weak London dispersion intermolecular force, which explains why graphite is so soft and easily broken.

Categories of Organic Compounds

Organic compounds all contain carbon atoms. There are only a few carbon compounds, such as organic compounds like NaCO3 and the oxides of carbon (CO and CO2), that are not considered organic. Because of carbon’s ability to form different combinations of single, double, and triple covalent bonds, the number of possible carbon compounds is virtually unlimited. There are more than 4 million naturally occurring and man-made organic compounds currently known.

Carbon can fill its valence energy level by sharing a total of four pairs of electrons. This means that a given carbon atom can form four single bonds, two single bonds and one double bond, two double bonds, or one triple bond and one single bond.

REVIEW SLIDES AT THE BOTTOM OF LESSON 08.05

Biochemistry

Biochemistry, as its name suggests, is a field of science that combines biology and chemistry. Specifically, it is the study of the chemistry involved with living organisms. This means that biochemists study the atoms, molecules, and chemical reactions that are found in, or affect, living organisms.

Biochemistry is much more than the study of the molecules found in living systems. It is a study of the reactions that produce or use these substances, and it helps answer questions about how organisms live, move, function, and respond to stimuli.

Every living cell is a biochemical factory, building and dismantling molecules in a variety of chemical reactions. The energy needed to fuel these reactions is provided by the food that the organisms eat. All of the biochemical reactions that occur in a given organism are collectively called its metabolism

Metabolism: All of the biochemical reactions that occur within a given organism, and the reactions are organized into metabolic pathways to be studied and tested.

Ex: I don’t gain weight easily because I have a really fast metabolism

Biotechnology

Biotechnology is the application of the knowledge of biochemistry to create new products or processes that are useful to humans. Advances in biotechnology have affected our lives in many ways. A few examples of biotechnology include:

Biotechnology touches our lives in many ways. Listed below are some highlights.

Agriculture: Biotechnology allows scientists to transfer genes from one plant species to another. For example, a scientist might transfer a gene that gives one kind of plant a resistance to salt into a crop plant. The crop plant may then be able to grow under higher salt conditions.

Forensics: Forensic scientists can get DNA from blood, skin cells, and other bodily substances. They can compare the DNA in samples found at a crime scene with DNA from possible victims and suspects. By comparing DNA sequences, they can link suspects and victims to crime scenes

Genetic Research: Many diseases are caused by specific genes. Scientists can screen people for some of these genes. This information can help people make important decisions about their health.

Drug Research: Scientists are developing devices that use computers and living cells to study the effects of different drugs. These devices allow scientists to greatly reduce the number of animals used in drug research.

Vaccines and Medicine: Biotechnology can help scientists produce vaccines and other drugs. Scientists can genetically modify bacteria so that they produce the vaccine or drug in very large quantities.

GOOD

LUCK!!