Chapter 11Chemical Reactions

Note Taking Tips!

• Paraphrase, paraphrase, paraphrase!

• Use symbols, arrows, pictures, and abbreviations whenever possible.

• Write side notes to help you remember concepts.

What is a chemical reaction?– Occur every minute of every day!– When one or more reactants change into one

or more products. – Characterized by the breaking of bonds in

reactants and formation of bonds in products

Law of Conservation of Mass

• In any physical or chemical reaction, mass is conserved; mass can be neither created nor destroyed

Chemical Reactions

• Chemical reactions are described by chemical equations. • Skeleton Equation: chem equation that doesn’t indicate relative

amounts of reactants and products.

Fe + O2 Fe2O3

Reactants Products

It needs to be balanced!!!

Draw this one

It means the reaction is reversible

• Catalyst: a substance that speeds up the reaction but is not used up in a reaction. – Neither a reactant nor a product– Written above arrow in chem equation.

MnO2

H2O2(aq) H20(l) + O2(g)

Balancing Act

• Bicycle scenario

Balancing Chemical Equations

• A chemical reaction where each side of the equation has the same number of atoms of each element and mass is conserved.

Fe + O2 > Fe2O3

Steps to Balancing1. Count atoms on each side. Count polyatomic ion as one unit

if it appears unchanged on right.

2. Balance elements one at a time using coefficients– Balance elements that appear only once 1st

– Never change subscripts

3. Check work and make sure all coefficients are in lowest possible ratio.

H2 + O2 > H2O

Let’s try some!

Let’s try some!

1. _____ S + _____ O2 --> _____ SO2

2. _____ Na + _____ O2 --> _____ Na2O2

3. _____ Hg + _____ O2 --> _____ HgO

4. _____ Ag2O --> _____ Ag + _____ O2

Let’s try some!

Practice

Practice

11.2 Types of Chemical Reactions

Concept map

•5 general types– Combination– Decomposition– Single-replacement– Double-replacement– Combustion

Concept map instructions

• Get basic definition

• Write at least one chemical reaction

• Describe the demonstration reaction

Combination

• When 2 or more substances react to form a single new substance.

2Mg + O2 > 2MgO

Decomposition

• When a single compound breaks down into 2 or more simpler products.

• 1 reactant, 2 or more products• Usually require heat, light, or electricity to occur.

2HgO > 2Hg + O2

Single-Replacement

• When 1 element replaces a second element in a compound.

2K + 2H2O > 2KOH + H2

Look at the switch!

Double-Replacement

• An exchange of positive ions between 2 compounds.

• Usually produces one of the following– A precipitate– A gas– water

• Remember: positive ions=cations=on left side of a compound

• Na2S + Cd(NO3)2 > CdS + 2NaNO3• 2NaCN + H2SO4 > 2HCN + Na2SO4• Ca(OH)2 + 2HCl > CaCl2 + 2H2O

Combustion• When an element or compound reacts with oxygen, it produces

energy in the form of heat and light. • Oxygen is always a reactant• The other reactant is often a hydrocarbon (something with hydrogen

and carbon)– CH4 methane– C3H8 propane– C4H10 butane– C8H18 gasoline

• CO or CO2 can also be products

2C8H18 + 25O2 > 16CO2 + 18H2O

Practice!

Your Task

• Dissecting a chemical reaction