Chemistry: Reactions and...

Daintrey’s Doings J 1

Chemistry: Reactions and Reactivity Atomic Theory 1. Chemical VS Physical Change

• Chemical Change: Is a change in which new substances are formed. A chemical change produces a set of chemicals with is different from the set of chemicals, which existed before the change.

o Not reversible o New substances and properties form o May see an energy change

Examples: Cooking, Burning….

• Physical Change: Is a change in the phase (state: solid, liquid, gas) of a substance, such that no new substances are formed. A physical change does not change the set of chemicals involved.

o Able to reverse o No new substance, properties don’t change o Energy may occur

2. The Atom/Molecule/Matter

• An atom is the smallest particle of an element that retains the properties of the element. (i.e Elements are made up of atoms)

• A molecule is two or more atoms joined together. Molecules can have only one type of atom (element) OR can have more than one type of atom (compound). Example: O2 (element) and H2O (compound)

• Matter is anything that has mass and volume. It (matter) can be

classified into pure substances and mixtures.

o Pure Substance: contains only one type of particle § Element: Pure substance that cannot be changed into

anything smaller. § Atom: Smallest part of an element § Compound: pure substance that consists of two or more

elements.


o Mixtures: two or more pure substances mixed together.

§ Heterogeneous mixture: not uniform in composition. You can see the different components in it. (i.e bits and bites)

§ Homogeneous mixture: uniform throughout. Cannot see the different components. (sugar water, pop, alloys, kool-aid)

• Subatomic particles are the particles that make up an atom. Look at the chart below:

3. Parts of the Atom- Subatomic Particles

Subatomic Particle Charge Mass Location Proton Positive (+ve) Has mass Nucleus Neutron Neutral Has mass Nucleus Electron Negative (-ve) Virtually no mass Orbits around the nucleus

• Protons and neutrons are held tightly together in

the center of the atom in a tiny region called the nucleus.

• Electrons exist in a region around the nucleus in regular patterns called shells or energy levels.


• The number of protons in a nucleus defines what that element is. You can change the number of electrons and neutrons, but protons define what an element is.

4. How to Calculate Protons, Neutrons, and Electrons

o Number of protons (p) = atomic number

o Number of electrons (e) = number of protons (atomic #) in a NEUTRAL atom.

**In an ion (atom having a charge), can be more / less than the # of protons**

o # of neutron (n) = Atomic Mass – Atomic number (# of protons)

Atom Atomic Mass

Atomic Number

Protons Neutrons Electrons

Carbon Nitrogen Fluorine Chlorine Lithium


Sample Provincial Questions

5. Atom vs Ion: Atoms have the same number of electrons and protons. Ions gain or lose electrons to become charged. They do this to form ionic bonds between metals and nonmetals. Use the charge listed on the periodic table to see how many electrons are gained or lost. Metals tend to loose electrons and form positive ions (cations) Nonmetals tend to gain electrons and form negative ions (anions)

Element Atomic Number

Number of Electrons in the Neutral atom

Ion Charge

Number of electrons in the

ion Fluorine 9 9 -1 10 Lithium 3 3 1+ 2 Sodium Magnesium


Oxygen Rubidium 6. Organizing and knowing your Periodic Table

• Some metals and non-metals can only form an ion in one way. Calcium forms a cation by losing 2 electrons to become Ca+2.

• Common ions formed by elements are shown in the upper right hand

corner of the elements box in the periodic table.

• Notice how some metals have more than one possible ion. We call these metals multivalent.

• Includes both metals and non-metals…separated by the staircase of fun. Metals on the left, non-metals on the top right.

• Elements are listed according to its atomic number. Each row is called

a period and each column is called a group or family.

• Elements in the same group / family have similar properties. What follows are the families / groups that you have to remember:

• Transition metals (multivalent): Block of elements that include groups

3 to group 12

• NON-METALS o UP a Group: In NON-METALS reactivity INCREASES as you

go UP Fluorine? A greedy, impatient beast when it comes to electron exchange manners.

o ACROSS a Period: In NON-METALS reactivity INCREASES as you go ACROSS

• METALS o DOWN a Group: In METALS

reactivity INCREASES as you go DOWN

o ACROSS a Period: In METALS reactivity


DECREASES as you go ACROSS

Family Name

Elements Common Ion Charge

Group Number

Nobel Gases Special! DO

NOT react with anything.

He Ne Ar Kr Xe Rn None 18

Alkali Metals

Li Na K Rb Cs Fr +1 1 Highly reactive!

Alkaline Earth Metals

Be Mg Ca Sr Ba Ra +2 2

Halogens F Cl Br I At -1 17 Hydrogen H +1 or -1 1/17

* Hydrogen appears as both a metal and non-metal on the periodic table. It can use either covalent or ionic bonds* 7. Bohr Model Diagrams

• Niels Bohr discovered that electrons were arranged in energy levels or shells in specific patterns.

• Each shell can hold a certain number of electrons, no more, no less.

• A Bohr diagram (Bohr model) is a diagram (model) that shows how

many electrons are in each shell surrounding the nucleus.

• In Science 10, you only have to be able to draw and interpret the Bohr models for the first 20 elements. Use the following rules:


Rule for first 20 elements: 1st shell= 2 electrons 2nd shell = up to 8 electrons 3rd shell = up to 8 electrons 4th shell = 2 electrons ***not 100% true…but good enough for Sci 10***

• In drawing Bohr diagrams, start by finding out how many p, e and n’s there are. Electrons are the most important, as they are what really is shown.

For example: Bohr Model of Aluminum (Al) Protons Electrons Neutrons Bohr Model

How about a Sulphur ion with a –2 charge [S]-2? Protons Electrons Neutrons Bohr Model

Sample Provincial Exam Question: The Bohr diagram represents A. A sodium ion B. A fluoride ion C. A helium atom D. A Fluorine atom • The outside shell of a Bohr diagram is called the valence shell


• Every element on the periodic table is trying to get a full valence shell. For most elements that equals 8 electrons in the outer shell. This is called a “stable octet”

• Elements become ions trying to get to the 8 electrons in their outer

shell. They either gained extra electrons or give a few away. If you already have 8 electrons in your outer shell do you react well with other elements? * Think Noble Gases!

• There are patterns on the periodic table to tell you how many

electrons are in the outer “valence” shell of an atom. Column 1 = 1 valence electron Column 2 = 2 valence electrons Column 13 = 3 valence electrons Column 14 = 4 valence electrons Column 15 = 5 valence electrons Column 16 = 6 valence electrons Column 17 = 7 valence electrons Column 18 = 8 valence electrons

Example: Potassium Atom:

Ion:

8. Bonding Diagrams for Bohr Diagrams

• There are two types of chemical bonds, ionic and covalent. Atoms from compounds when the move close together and their valence electrons interact.


• In an ionic bond, electrons are transferred. The metal will transfer one or more electrons to the non-metal. Ionic compounds are made up of 1 metal and 1 non-metal. See the diagram below for Sodium Chloride (table salt).

Let’s draw one together:

MgCl2

• In a covalent bond, electrons are shared. A covalent compound is

formed when two non-metals share electrons.

• Electrons involved in bonding are sometimes called bonding electrons

(shocking) and electrons that are in valence shells, but not involved in the bond are called lone pairs.


Let’s draw one together: CH4

Sample Provincial Exam Question: Which two of the following atomic models represents elements that can easily combine with each other to form a covalent compound?

A. I and II B. I and IV C. II and III D. III and IV

9. A Lewis Diagram / Structures illustrates chemical bonding by showing only the valence electrons and the chemical symbol. Rules for Lewis Diagrams:

1. Dots represent electrons and are placed around the elements like dots on a compass.

2. Electron dots are placed singularly until the fifth electron is reached, then they are paired.


Bohr Lewis Dot Diagram (valence shell only) Oxygen Oxygen

Fluorine Fluorine

Argon Argon

Sample Provincial Exam Question: The Lewis diagram to the right represents either A. A helium atom or a lithium ion B. A neon atom or a fluorine atom C. An argon atom or a sulphide ion D. A potassium atom or a calcium ion Draw the following:

Hydrogen

Carbon Nitrogen

Hydrogen +1

Fluorine -1 Chlorine -1


10. Lewis Dot Diagrams for Ionic and Covalent Bonds

Rules for ionic compounds are as follows:

1. Draw the diagram for the positive ion (metal) using the common ion charge found on the periodic table.

2. Draw the diagram for the negative ion (non-metal) using the common ion charge found on the periodic table.

3. Remember that the metal will have lost electrons and the non-

metal will have gained them.

4. Put brackets around each symbol with the charge written outside the bracket on the top right.

Try these…

MgO BaBr2


Rules for covalent compounds are as follows:

1. Draw out the element without using charges.

2. A line will represent the bond between the two elements sharing electrons.

Try these… HF

CH4

NH3

C2H6

• A diatomic molecule is a pair of atoms that are joined by covalent

bonds. Some elements are more stable joined together than by themselves. There are 7 diatomic elements that you will have to remember. They are: H2, O2, F2, Br2, I2, Cl2 and N2

HOFBrINCl

• Can you see why we say hockey stick and puck? Look at the periodic table.

• Always covalently bonded. (non-metals)

• Why do they always appear in pairs? Well if you look at their Lewis dot diagrams they all have the need for one valence electron to satisfy a shell. Let’s look at a few:


Flourine

Nitrogen

Hydrogen

Iodine

11. Writing Formulas for Ionic Compounds:

• The language of chemistry is based on abbreviations for the name of

the elements. Such abbreviations are called chemical symbols. • The first letter in the symbol is ALWAYS in upper case (capitals).

Second letters, if present, are ALWAYS in lower case.

THERE ARE TWO METHODS!!! Algebraic Sum (Never fails) In this method, the combining capacities (common charges) have to add to zero. Here are the steps. We’ll look at Calcium + Fluorine or (Calcium Fluoride)

1. Write the symbols for the elements with their combining capacities.

Ca+2 F-1 *Note that a positive can only combine with a negative.*


2. The algebraic sum of the charges in a compound is zero. In other words, the charges should balance to zero.

As we can see, the Calcium is +2 and the Fluorine is -1. Thus, you will need 2 fluorine atoms for every 1 Calcium atom. Ca+2 F-1 F-1 +2 -2 = 0 As we can see, the Calcium is +2 and the Fluorine is -1. Thus, you will need 2 fluorine atoms for every 1 Calcium atom. The formula is CaF2 Criss-Cross Apple Sauce! As the name implies, this method involves a criss-cross. In this case, it is the combining capacities that are crossed. Here are the steps. Let’s look at Calcium + Fluorine again.

1. Write the symbols for the elements with their combining capacities.

Ca+2 F-1

2. Crossover the combining capacities as

follows: Ca+2 F-1

CaF2 (Note: + & - cancel out) **Caution: if you use this method, you will have to reduce the formula to lowest terms, just like fractions in math class.***


Example: Calcium and Oxygen Ca+2 O-2 (OR Calcium Oxide) Ca2O2 Ca2O2 must be reduced!!!!! The formula is CaO 12. Ionic Naming 1. Always write the metal ion first 2. Add the nonmetal second and add “ide” to it

Examples: Formula Name NaCl

BaBr2

AlF3

Mg3N2

13. Polyatomics

• Poly = Many • Atomics= Atoms

• In chemistry, there are groups of atoms that ‘act’ as a single atom.

These are called polyatomic ions

• Recall that metals have a positive charge (cation) and non-metals have a negative charge. Most polyatomics are non-metals, with ammonium (NH4

+) being the exception.


• The rules for writing formulas involving polyatomic ions are done in exactly the same way. The positive (metallic) ion is written first, followed by the negative ion. The algebraic sum must be equal to zero. (most polyatomic ions are negative ions)

How to use polyatomic ions for naming:

KCH3COO

(NH4)3P

How to use polyatomics for formula writing

Name Ions Formula

Sodium Bisulphide

Calcium Phosphate

Calcium Carbonate


14. Multivalent Naming

• Multivalent means that there is more than one charge

• Use Roman numerals when naming compounds if the periodic table lists more than one charge.

• Recall that a multivalent element is one with more than one possible

charge (combining capacity).

• In order to write the formula, you MUST know which combining capacity to use. Luckily, it is in the name...Roman Numerals J

• Note that the combining capacity is given in roman numerals following

the element. Roman Numerals: I =1 II =2 III =3 IV = 4 V =5 VI =6 The steps involved are exactly the same. If you use the criss-cross method, make sure you REDUCE J.

Example #1: Gold (III) oxide The roman numeral only have to do with the metal or the positive combining capacity. Method 1 Method 2 Au+3 O-2 or Au+3 O2- Au+3 O-2 O-2 Au2O3 +6 -6 = 0 Au2O3


Example #2: Nickel (II) phosphate Method 1 Method 2 Ni+2 PO4

-3 or Ni+2 PO4-3

Ni+2 PO4-3

Ni+2 Ni3(PO4)2 +6 -6 = 0 Ni3(PO4)2 ** Polyatomics ions are in brackets when there is more than one** Try these:

Compound Name Titanium (III)

Oxide

Iron (III) Oxide Iron (IV) Sulphide

Ions & charges

Work shown

Formula

15. Covalent Compounds Naming and Formula Writing

Covalent compounds share electrons between two nonmetals.

Here are some rules that will help…


Rule 1: Write the name of the elements in the same order that they appear in the formula. The more metallic element is named first.

Rule 2: Drop the last syllable in the name of the final element

and add –ide.

Rule 3: Add prefixes to the name of each element to indicate the number of atoms of that element in each molecule of that compound. A prefix is ALWAYS added to the SECOND element, but only added to the first element if there is more than 1 atom.

Naming:

CO2

CO

CCl3

S2F10

H2O

You are given the following table in your data booklet to talk about the prefixes needed when naming covalent compound

carbon tetrabromide

sulphur trioxide

tetraphosphorus trisulfide

Diarsenic pentoxide

Diphosphorus pentoxide


Sample Provincial Exam Questions What is the formula for the compound dinitrogen pentoxide? A. NO4 B. NO5 C. N2O4 D. N2O5

16. Writing Chemical Equations: Now that we know how to name and write formulas this will help us write chemical equations. You simply have to convert from formula to words or from words to the formula Reactants + Reactants à Products Two things to be aware of when writing a chemical equation

a. Balancing coefficients: integers placed in front of formulas to balance the ratios in which the chemicals are consumed and produced.

b. States: letters indicating the state of the compound. (g) = gas, (l)= liquid (s)= solid

One water molecule H2O

Two water molecules 2H2O

Three water molecules 3H2O

One Hydrogen peroxide H2O2


Law of Conservation of Mass: Mass cannot be created nor destroyed during a chemical reaction. The Amount of reactants must be equal to the mass of the products in a closed system. (What happens in an open system?)

1. Break it into sides…left and right 2. Right the atoms down the left side as they appear in the

equation. Keep polyatomics together!!!! 3. Do the same to the right side

(right down the atoms…SAME ORDER!) 4. Balance major atoms first (Metals / Non – Metals) 5. Balance water (H2O) and oxygen (O2) last.

Examples: ___ Al + ___ O2 → ___ Al2O3 ___ N2 + ___ H2 → ___ NH3

___ (NH4)3PO4 + ___ NaOH → ___ Na3PO4 + ___ NH3 + ___ H2O


Iron Solid plus Copper (II) Chloride yields Iron(II) Chloride plus copper Solid Sample Provincial Exam Questions Which set of ordered coefficients balances the equation below?

A. 3, 1, 3, 1, 1 B. 3, 1, 1, 1, 3 C. 3, 1, 1, 3, 1 D. 3, 1, 1, 3, 3

17. Classifying Substances: Another way of classifying substances besides them as ionic or covalent is to classify them as acidic, basic, or neutral. We can do this using the pH scale, which is a numbering system to measure how acidic or basic a solution is.

Type of Solution Example pH range

Acid Lemon Juice, Stomach acid, fruits

Value of less than 7

Base Cleaners, bleaches, ammonia

Value of more than 7

Neutral Purified Water Exactly 7


a. pH Indicators

• Chemicals which change colour depending on the pH of the solution they are placed in are called pH indicators.

• Litmus is a common one which is usually put into paper format so that it can determine if a solution is acidic or basic.

• Litmus paper can be blue or red. In an acid litmus paper is always red

and in a base litmus paper is always blue!

Sample Provincial Exam Questions:

The water from the Great Salt Lake in Utah has the following effects on acid-base indicators:

What is its pH?

A. 8 B. 10 C. 12 D. 14

What colour would bromthymol blue turn in acetic acid?

A. Red B. Blue C. Yellow D. Colourless


18. Naming Acids:

Formula Chemical Name Formula in solution

Name of the Acid

HF Hydrogen Fluoride

HF (aq) Hydrofluoric Acid

HCL Hydrogen Chloride

HCL (aq) Hydrochloric Acid

HI Hydrogen Iodide HI (aq) Hydroiodic Acid HClO4 Hydrogen

Perclorate HClO4 (aq) Perchloric Acid

Most acids end their name in ‘IC’. Some acids that involve polyatomics do not. Here is the rule for polyatomics:

a. drop the “Hydro” a. If it ends in “ate” the ending of the acid will be “ic” b. If it ends in “ite” the ending of the acid will be “ous”

If you –ate acid it would be icky If you bite candy it would be tremendous Name the below acids:

Formula Polyatomic Name Acid Name

H2SO4

H2SO3

HNO3

H3PO4

19. Naming Bases

Formula Chemical Name Common Name Example of Use

NaOH Sodium Hydroxide

Caustic Soda Oven Cleaner


Mg(OH)2 Magnesium Hydroxide

Milk of Magnesia Antacids

Ca(OH)2 Milk of Lime Sugar refining,

leather tanning KOH

Lye Soap

Differences and Similarities between Acids and Bases

Property Acid Base Taste Sour Bitter Touch Burn your skin Slippery

Indicator Tests

Blue Litmus paper turns red Phenolphthalein is Colourless

Red litmus turns blue Phenolphthalein turns pink in stronger bases

Reactions with metals Corrode metals No reaction Electrical Conductivity Conducts electricity Conducts Electricity

pH Less than seven More than seven

Production of ions Produces H+ ions in a solution

Produces OH- ions in a solution

20. Salts

a. Salts are a class of ionic compounds that can be formed when an acid and a base react together.

b. Salts are produced from Acid Base Neutralizations, which are part of the 6 types of reactions.

c. To get a salt from an acid base neutralization you take the positive ion from the base and add it to the negative ion of the acid

Let’s do an example together: HCl + NaOH à Acid + Base à Salt + Water


21. How to make Acids or bases:

A. A base comes from a metal oxide mixed with water Example:

Na2O (S) + H2O à 2NaOH (aq)]

Metal oxide + water àSodium Hydroxide

B. An acid is made from a non-metal oxide mixing with water Example:

SO2 (g) + H2O à H2SO3 (aq)

non-metal oxide + water à Sulphurous Acid Sample Provincial Exam Question: Which of the following, when dissolved in rainwater, cause acid precipitation? A. Alkali metals B. Metal oxides C. Non-metal oxides D. Alkaline earth metals

21. Organic Compounds

• Organic refers to almost all carbon containing

compounds. Inorganic refers to those that do not contain carbon.

• Organic compounds do not just contain carbon,

also have oxygen, hydrogen, sulphur and nitrogen.


• You can recognize organic compounds by looking at the formula. If you see a lot of C and H’s bonded together, good chance that it is organic.

• Hydrocarbons are organic compounds that only contain carbon and

hydrogen. Wow…shocking!!

• 1000’s upon 1000’s exist. Some hydrocarbons are flammable and can be used as fuel.

• Why is carbon used in organic compounds? How many bonds are

available in a Lewis dot structure of carbon?

• Organic compounds are named by the number of carbons they contain (sort of). Here are the prefixes (to the left).

• Alcohols contains C, H and O’s. You can tell an alcohol right away from an attached ‘OH’ group. The name also ends is “-ol” we’ll get to it!

• Ethanol is used in beverages and in some disinfectants.

• In large quantities, ethanol can be fatal.

Let’s try a few together: Name # of carbons Molecule

Methane

Methanol

Heptane


Pentanol

22. Types of Chemical Reactions

• There are 6 types of reactions that you need to know about.

1. Synthesis 2. Decomposition 3. Single replacement 4. Double replacement 5. Neutralization 6. Combustion.

• The most difficult part of this section will be predicting what the products are. In order to do this, you MUST be able to recognize the type of reaction based on the reactants.

Synthesis (or Combination)

• A SYNTHESIS or combination reaction involves the combination of two or more substances to form a compound.

• Synthesis reactions can be represented by the general equation: A + B → AB

Where A and B represent elements and AB is a compound.

• Reactants are two elements and product is compound made of two elements joined together. Use the most common charges for each ion.


e.g. C(s) + O2(g) → CO2(g)

2H2(g) + O2(g) → 2H2O(g)

Fe + S → Decomposition

• A DECOMPOSITION reaction involves breaking down molecules into simpler substances.

• Decomposition reactions can be represented by the general equation:

AB → A + B

• Reactants are a single compound and products are the elements that make up the compound. (This is the reverse of a synthesis!!!)

e.g. 2H2O(l) → 2H2(g) + O2(g) NaCl(s) → Na(s) + Cl2(g) 2KCl (s) →

Single Replacement (Girlfriend / Boyfriend stealing!!!)

• A SINGLE REPLACEMENT reaction involves replacing one atom in a compound by another atom.

• Single replacement reactions can be represented by the general equation:

A + BC → B + AC (where A is a METAL) A + BC → C + BA (where A is a NON-METAL)


• Reactants are an element and a compound and products are an element and a compound. If “A” is a metal, it will replace the metal ion “B” in the compound. If “A” is a non-metal, it will replace the non-metal “C” in the compound.

Example: Br2 + CuI2 → I2 + CuBr2 2Al + CuCl2 → 3Cu + 2AlCl3 Cl2 + 2CsBr →

Double Replacement (Wife Swap!!!)

• A DOUBLE REPLACEMENT reaction involves an exchange of atoms or groups between two different compounds

• Double replacement reactions can be represented by the general equation:

AB + CD → AD + CB

ionic sol’n + ionic sol’n → ionic sol’n + ionic solid

The ionic solid that is produced is called a precipitate

• Reactants are two compounds and products are two compounds. Assume that reactants are made up of ions. Make up products by having positive ions (written first) exchanging partners. Pay attention to the charges of the ions when writing formulas of products.


Example: Cu(NO3)2 + Na2S → CuS + 2NaNO3 FeCl3 + 3 NaOH → Fe(OH)3 + 3 NaCl

Neutralization (Acid Base Reaction)

• There is a special case of double replacement reaction that involves the reaction of an ACID with a BASE. These reactions are called Neutralization reactions. An acid has a chemical formula starting with “H” and bases have chemical formulas ending in “OH”.

• The positive part of the base is added to the negative side of the acid.

• Neutralization reactions can be represented by the general equation:

Acid + Base → Salt + Water

HX + MOH → MX + H2O

(The ‘H’ from the acid and the ‘OH’ from the base form the water, what’s left, is the salt)

Examples: HCl + NaOH → NaCl + H2O

H2SO4 + 2KOH → K2SO4 + 2H2O

Combustion of Hydrocarbons

• COMBUSTION is a general term referring to the rapid reaction of a substance with oxygen to produce large amounts of heat and light. An important case of combustion involves organic compounds whose formulas start with carbon.

• OXYGEN must be present!

• When a HYDROCARBON (a compound made up of C and H) undergoes combustion, the products are carbon dioxide, CO2, and water, H2O.

• The combustion of a hydrocarbon can be represented by the general equation:


Hydrocarbon + O2 → CO2 + H2O

• Reactants are hydrocarbon (C–H) and oxygen (O2) and products are carbon dioxide (CO2) and water (H2O).

Examples: C5H12 + 8 O2 → 5 CO2 + 6 H2O

2 C2H2 + 5 O2 → 4 CO2 + 2H2O

• The summary below will help you (hopefully) remember the 6 types of

reactions.

TYPE HOW TO RECOGNIZE REACTANTS HOW TO PREDICT PRODUCTS

Synthesis or Combination 2 elements combine elements into one

compound

Decomposition 1 compound Break compound down into its

elements

Single Replacement Element + Compound Interchange metals (or

nonmetals) present

Double Replacement Compound + Compound Interchange positive ions in

compounds

Neutralization Acid + Base Water is one product;

remaining ions combine to form

a salt

Combustion of Hydrocarbon Compound starting with “C” +

O2

CO2 + H2O (if H present) + SO2

(if S present)

NO2 (if N present)


• Try to predict the following reactions and balance. Have fun J

1. AgNO3 + Na2CrO4 →

2. Li + N2 → 3. C6H12O6 + O2 → 4. H2O → 5. Cl2 + NiBr2 → 6. H2SO4 + KOH →


23. Factors Affecting the Rate of Chemical Reactions • Rate of reaction refers to how long it takes the reactants to turn into

products. • A rate describes how quickly or slowly a change occurs. • The following factors affect reaction rate:

1. Temperature: When you increase the temperature of a system you are increasing the number of particle collisions because the particles are moving faster (more kinetic energy).

Some reactions need the substance to be heated to occur. This means they require energy to be started.

2. Concentration: When concentration is increased the reaction rate is increased. This is because there are more particles in the solution and therefore more particles to make the reaction happen (have a collision).

3. Surface Area: surface area is the measure of how much area

of an object is exposed. Powders have much more surface area than solid blocks of the same material. The greater the surface area the faster the reaction rate because there is more of the surface exposed to make the reaction occur (again, think collisions).

4. Catalyst: A catalyst is a substance which speeds up the rate of

reaction without being used up in the reaction. A catalyst is usually not written in the chemical equation because it doesn’t change within the course of the reaction (regenerated…you will end with as much as you started with).

Catalysts are found on both the reactant and product sides!

• A catalytic Converter is a device in your car which takes some of the

harmful carbon monoxide and nitrogen oxides and converts them to less harmful gasses.


• A catalytic converter has two reaction chambers. • The first chamber uses platinum and rhodium (as a catalyst) to reduce

the NOx emissions. When a NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms then bind with other nitrogen atoms that are stuck on the catalyst, forming N2.

2NO N2 + O2 or 2 NO2 N2 + 2O2 • The second chamber uses platinum and palladium as catalysts to

reduce the unburned hydrocarbons and carbon monoxide. 2CO + O2 2CO2 Sample Provincial Exam Question: Karen notices that cupcake recipes always have shorter cooking times than larger cakes. Which of the following factors accounts for this observation?

A. Presence of a catalyst B. Increased surface area C. Increased temperature D. Increased concentration

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