Investigating Chemical Reactions

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

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

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)

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)

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

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)

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.

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)

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)

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