1. Classifying
Chemical Reactions

2. Classifying Chemical Reactions
Reactions are either classified by:
how much energy is given off or absorbed
how the atoms are rearranged
Chemical Reactions and Energy
Exothermic Reactions
produce energy (heat, light, sound)
e.g.
CH4(g) + O2(g)  H2O(g) + CO2(g) + energy
Endothermic Reactions
absorb energy (heat, light, sound)
e.g.
CaCO3(s) + energy  CaO(s) + CO2(g)

3. Chemical Reactions and Atom Rearrangement
Synthesis Reactions (Combination)
2 or more substances combine to form a compound
General Formula:
A + B  AB
1 PRODUCT
e.g.
S(s) + O2(g)  SO2(g)
2 elements
2SO2(g) + O2(g)  2SO3(g)
1 element, 1 compound
SO3(g) + H2O(l)  H2SO4(g)
2 compounds
Decomposition Reactions
1 substance breaks down into 2 or more simpler substances
General Formula:
AB  A + B
1 REACTANT
e.g.
2H2O(l)  2H2(g) + O2(g)

4. Single Replacement Reactions (Displacement)
A combined element in a compound is replaced by an uncombined element.
General Formula:
Z + AB  AZ + B
Metals replace metals; Non-metals replace Non-metals
e.g.
Br2(l) + 2NaCl(aq)  2NaBr(aq) + Cl2(g)
2Al(s) + Fe2O3(s)  2Fe(l) + Al2O3(s)
Double Replacement Reactions (Ionic)
Elements in different compounds replace each other (exchange places)
General Formula:
AB + XY  AY + XB
e.g.
2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq)
2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq)
One of the products often forms a precipitate. (an insoluble solid that separates from the solution)

5. Neutralization (Acid-Base)
A type of double replacement reaction that involves an acid reacting with a base to produce water and a salt.
General Formula:
Acid + Base  Water + Salt
e.g.
HCl(aq) + NaOH(aq)  HOH(l) + NaCl(aq)
HCl(aq) + NaOH(aq)  HOH(l) + NaCl(aq)
Combustion
A special type of exothermic reaction where oxygen is a reactant and oxides are produced with a large amount of energy.
e.g.
CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) + energy
2H2(g) + O2(g)  2H2O(l) + energy
2Mg(s) + O2(g)  2MgO(s) + energy

6. Assignment In Class: Homework: Classify Workbook Pages 105 & 106
Balance Workbook Pages 105 & 106
Classify Workbook Pages 107 & 108