CHEMICAL REACTIONS

7.1 SKIP MOLES

True False Statement True False

Products are on the left, and yield reactants on the right of a chemical

equation

Law of conservation of mass says that matter (elements) cannot be

created or destroyed

When balancing equations you CAN change the subscripts, but NOT the

coefficients

Avogadro's number is 6.02 x 1023 which is about a mole

Cu + O2 CuOIs balanced

Chemical Reactions

Chemical reactions change substances into new substances with new chemical and physical properties

Ways to know a chemical reaction is occurring: A release of gas A color change Production of light and/or heat The production of a precipitate (solid)

Parts of Chemical Reactions

The Law of Conservation of Mass States that no matter can be created nor

destroyed in a chemical reaction

# on the left = # on the right

Two parts of a chemical reaction

Reactants: a substance or molecule that participates in a chemical reaction Usually found on the left side of an equation

Products: a substance that is formed in a chemical reaction Usually found on the right side of an equation

Parts of a chemical equation

2 H2 + O2 2 H2O

Atoms are rearranged in chemical reactions to make new substances by making or breaking bonds.

Products Reactants

Coefficient

Subscript

Chemical Equations

Chemical equation: A representation of a chemical reaction that

uses symbols to show the relationship between the reactants and products

CH4 + O2 CO2 + H2O

When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may NOT change the subscripts.Changing the subscripts changes the

compound!! Subscripts are determined by the valence

electrons (charges for ionic or sharing for covalent)

The subscripts tell you how many atoms of a particular element are in a compound.

The coefficient tells you about the quantity, or number, of molecules of the compound

1. Write the correct formula for the reactants and the products.

2. Find the number of atoms for each element on the left side. Compare those against the number of the atoms of the same element on the right side.

3. Determine where to place coefficients in front of formulas so that the left side has the same number of atoms as the right side for EACH element

4. Check your answer to see if: The numbers of atoms on

both sides of the equation are now balanced.

The coefficients are in the lowest possible whole number ratios. (reduced)

Write the equation that describes the burning of magnesium in air to form magnesium oxide.

Magnesium + Oxygen (air) Magnesium Oxide

Mg + O2 MgO

1 Mg 1 Mg 2 O 1 O

2

2

2

Balanced!

Potassium metal reacts violently with water to produce potassium hydroxide and hydrogen gas.

Potassium + Water Potassium Hydroxide + Hydrogen Gas

Math Practice pg 195

1. Balance the production of hydrogen chloride from hydrogen and chlorine

Math Practice

Balance H2O2 H2O + O2

Mg + HCL H2 + MgCl2

Math Practice

Ethylene, C2H4 burns in the presence of oxygen to produce carbon dioxide and water vapor. Balance.

Moles

(Mol) is the amount of subatnce that contains about 6.02 x 1023 particles of that substance.

Called Avagardo’s # Usually atoms,

ions, or molecules

Molar mass- mass of 1 mole of a substance

TYPES OF REACTIONS

Ch. 7.2

True False Statement True False

A synthesis reaction is when a compound breaks down into 2 or

more elements

In single replacement 1 pair switches places, and usually has 2

compounds on both sides

Combustion reactions always yield heat, light and water

Oxidation reactions gain electrons, while reduction lose electrons

AB A + BIs decomposition

Types of reactions

5 Types of Reactions Synthesis Single Double Decomposition Combustion

Synthesis

Synthesis Reaction: A reaction in which two or more substances combine to form a new compound

A + B AB

Example: 2Na + Cl2 2NaCl

Decomposition

Decomposition Reaction: A reaction in which a single compound breaks down to form two or more simpler compounds.

AB A + B

Example: 2H2O 2H2 + O2

Single Displacement

Single-Displacement Reaction: A reaction in which one element or radical

takes the place of another element or radical in a compound

AX + B BX + A

Example: 3 CuCl2 + 2Al 2AlCl3 + 3Cu

Double Displacement

Double-Displacement Reactions: A reaction in which a gas, solid, or a

molecular compound forms from the apparent exchange of atoms or ions between two compounds

AX + BY AY + BX

Pb(NO3)2 + K2CrO4 PbCrO4 + 2 K2 NO3

Combustion

Combustion Reaction: The oxidation of an organic compound in which heat is released Also known as

“burning” Always contain a

hydrocarbon and oxygen from the air as reactants

Always produce carbon dioxide, water, and heat

CH4 + 2O2 → CO2 +

2H2O + heat

LEO says GER!!!

Electrons are sometimes transferred in chemical reactions These reactions

are called oxidation-reduction reactions (REDOX reactions)

Oxidation Substances that

lose electrons are oxidized

Reduction Substances that

accept electrons are reduced

LEO-Lose Electrons =

Oxidation

GER-Gain Electrons =

Reduction

Oxidation or Reduction?

Fe changes to Fe2+ oxidation

Pb4+ changes to Pb2+ reduction

F changes to F1- reduction

Cr2+ changes to Cr3+ oxidation

Mg2+ changes to Mg reduction

ENERGY CHANGE AND REACTION RATES

7.3/4

True False Statement True False

Endothermic releases energy/forms bonds, while exothermic absorbs

energy/breaks bonds

Increasing temperature speeds up the reaction rate

The smaller the surface area and concentration, that faster the

reaction rate

A catalyst is a substance that speeds up a reaction without being

consumed

Reaction rate, is the rate at which products turn into reactants

Energy is released or absorbed

Absorbs energy Energy is required

to break bonds

Releases energy Energy is greater

than energy needed to break bonds

Endothermic Reaction Exothermic Reaction

Conservation of Energy

Energy is not created or destroyed in endothermic and exothermic reactions

Total energy at beginning = total energy at end

Reaction Rate

Rate at which reactants change into products over time

How fast reactants are being consumed How fast the products are being formed How fast energy is absorbed or released

Factors Affecting Reaction Rate Temperature

in temp= in rate Faster particles

in temp= in rate Slower particles

Surface Area in S.A= in rate

More collisions

Factors Affecting Reaction Rate Stirring

collisions= in rate

Ex: Washing machine

Concentration # of particles in a

given volume in conc.= in rate in pressure= in

rate gases

Factors Affecting Reaction Rate

Catalyst Affects substance

w/out being used up

Speeds up reaction

Written over yield arrow

EQUILIBRIUM

Ch 7.5

True False Statement True False

Means an equation is reversible/at equilibrium

Equilibrium means the forward and reverse paths of the reaction take

place at the same rate

There are 3 types of equilibrium-chemical, physical and atomic

La Chatelier said when a change is introduced, the equation will do the

opposite

Temperature, pressure, and concentration affect equilibrium

Equilibrium

State in which the forward and reverse paths of change take place at the same rate Physical and Chemical

Types of Equilibrium

Opposing physical change takes place at the same time

Opposing chemical changes take place at the same time

Physical Chemical

La Chatelier’s Principle

When a change is introduced to a system in equilibrium, the equilibrium shifts in the direction that relieves the change

Factors Affecting Equilibrium Temperature

in temp will shift in the direction that removes heat from the system

Pressure in pressure will

shift in the direction that decreases the pressure of the system

Factors Affecting Equilibrium Concentration

Equilibrium will shift in direction that produces concentration