Chapter 8

Chemical Reactions

• What a chemical equation looks like: yields 2 Na (s) + Cl2(g) 2 NaCl (s)

coefficients symbols

state of matter

How to describe a chemical change

1. Word equations

Reactants Products

Examples:

iron + oxygen iron (III) oxide

2. skeleton equation

First step in an chemical equation

Does not show amounts

Uses common symbols

3. “Common symbols” a. solid (s)

b. liquid (l)

c. gas (g)

d. aqueous solution (aq)- substance dissolved in water

e. catalyst

1. Speeds up the reaction

2. Is not used up

3. Written on the arrow Δ –heat catalyst MnO4

f. Examples MnO2

H2O2 (aq) ----> H2O (l) + O2(g)

4. skeleton examples a. Iron(III) oxide reacts with carbon monoxide to produce iron and

carbon dioxide

b. Heating potassium chlorate in the presence of MnO2

produces oxygen gas and potassium chloride as a solid

Balancing Chemical Equations

1. 2H2(g) + O2(g) 2 H2O (l)

2. Only numbers you may write are coefficients.

3. YOU MAY NEVER CHANGE SUBSCRIPTS!

4. Leave H and O go until last.

5. Reduce if possible, lowest whole number ratios.

6. Examples:

a. AgNO3 + H2S Ag2S + HNO3

b. HCl + NaOH --> NaCl + H2O

c. Al(OH)3 + H2CO3 --> Al2(CO3)3 + H2O

d. Al + S8 --> Al2S3

e. N2 + H2 --> NH3

Types of Chemical Reaction

A. Combination reaction (synthesis)

1. Two or more elements combine to form ONE product

2. A + X AX 2K(s) + Cl2(g) 2KCl (s)

B. Decomposition

1. one reactant breaks into products

2. AX A + X

3. Ex.H2CO3 (aq) H2O (l) + CO2 (g)

C. Single displacement 1. A + BX AX + B

element + compound compound + element

2. Ex.

Cu + 2 AgCl CuCl2 + 2 Ag

D. Double displacement1. positive ions switch with positive ions

2. AX + BY BX + AY

3. NaOH + HCl NaCl + H2O

E. Combustion 1. always a hydrocarbon (C and H) added to

oxygen 2. products are always carbon dioxide and

water

3. Ex. 2 C2H6 + 7 O2 4 CO2 + 6H2O

F. See packet to do this

G. Net Ionic Equation

1. Spectator ions – “watch” do not really do anything

2. Break only (aq) ions apart

3. Do not break (s) apart

4. Examples:

a. AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

b. Pb (s) + AgNO3 (aq) Ag (s) +Pb(NO3)2(aq)

F. Combustion reactions

1. always reacts with oxygen

2. hydrocarbon (some form of CH) plus oxygen always gives

carbon dioxide and water

3. Examples:

a. C6H6 + O2