1. Investigating
Chemical
Reactions

2. Chemists classify reactions to make it easier to predict the products of reactions.

3. 2H2 (g) + O2 (g)  2H2O (l) + thermal energy
Synthesis Reactions
What does synthesis mean? (Think back to the ecology unit…)
Also called Combination or Composition Reactions
Basically, what goes in comes out combined
Can you think of any examples?
General Equation:
X + Y  XY
Example:
2H2 (g) + O2 (g)  2H2O (l) + thermal energy

4. Decomposition Reactions
What does decomposition mean? (Think back to the ecology unit again…)
Basically, what goes in is broken down into component parts.
Can you think of any examples?
General Equation:
XY  X + Y
Example:
2H2O (l) + thermal energy 2H2 (g) + O2 (g)

5. Practice Questions:
Identify each of the following reactions as exothermic or endothermic.
Indicate the type (synthesis or decomposition).
Balance the equation.
Example:
thermal energy + N2(g) + O2(g)  NO2(g)
Endothermic or Exothermic?
Endothermic (because input of energy)
Type?
Synthesis Chemical Reaction (because combine)
Balanced Equation:
thermal energy + N2(g) + 2O2(g)  2NO2(g)

6. Na(s) + Cl2(g)  NaCl(s) + thermal energy Endothermic or Exothermic?
Exothermic (release of energy)
Type?
Synthesis Chemical Reaction (combine)
Balanced Equation:
2Na(s) + Cl2(g)  2NaCl(s) + thermal energy

7. thermal energy + CH3CH2OH(l)  C(s) + H2(g) + O2(g)
Exothermic or Endothermic?
Endothermic (input of energy)
Type?
Decomposition Chemical Reaction (break down)
Balanced Equation:
thermal energy + 2CH3CH2OH(l)  4C(s) + 6H2(g) + O2(g)

8. Write skeleton equations for the following
Write skeleton equations for the following. Then tell if the reaction is synthesis or decomposition. Finally, balance the equation.

9. calcium + oxygen gas  calcium oxide Skeleton Equation: Ca + O2  CaO
Synthesis or Decomposition?
Synthesis Chemical Reaction
Balanced Equation
2Ca + O2  2CaO
Balanced Chemical Equation
2Ca(s) + O2(g)  2CaO(s)

10. Synthesis or Decomposition? Decomposition Chemical Reaction
copper(II) oxide  copper + oxygen gas
Skeleton Equation:
CuO  Cu + O2
Synthesis or Decomposition?
Decomposition Chemical Reaction
Balanced Equation
2CuO  2Cu + O2
Balanced Chemical Equation
2CuO(s)  2Cu(s) + O2(g)

11. More work/
Homework
Page 185 # 4 & 5
and
Page 189 # 3 & 4