Investigating Chemical Reactions

All chemical reactions involve the releaseor Absorption of energy. Energy can be in the form of heat, light, electricity and sound. Energy-releasing reactions are called exothermic. An example would be an explosion.

In an exothermic equation the energy Is written on the Product side Ex: C 6 H 12 O 6 + O 2  CO 2 + H 2 O + Thermal energy

Energy-absorbing reactions are endothermic. An example would be cooking, or cold packs. Chemists classify reactions to make it easier to predict the products of reactions.

Synthesis Reactions (also called Combination or Composition Reactions) General Equation: X + Y  XY Example: 2H 2 (g) + O 2 (g)  2H 2 O ( l ) + thermal energy 2H 2 (g) + O 2 (g)  2H 2 O ( l ) + thermal energy

Decomposition Reactions General Equation: XY  X + Y Example: 2H 2 O ( l ) + thermal  2H 2 (g) + O 2 (g) energy energy

Practice Questions: Identify each of the following reactions as exothermic or endothermic, and indicate the type and balance the equation.

thermal energy + N 2(g) + O 2(g)  NO 2(g) endothermic or exothermic? endothermic Type and balanced equation: thermal energy + N 2(g) + 2O 2(g)  2NO 2(g) Synthesis Chemical Reaction

Na (s) + Cl 2(g)  NaCl (s) + thermal energy endothermic or exothermic? exothermic Type and balanced equation: 2Na (s) + Cl 2(g)  2NaCl (s) + thermal energy Synthesis Chemical Reaction

thermal energy + CH 3 CH 2 OH ( l )  C (s) + H 2(g) + O 2(g) exothermic or endothermic? endothermic balanced equation: thermal energy + 2CH 3 CH 2 OH ( l )  4C (s) + 6H 2(g) + O 2(g) Decomposition Chemical Reaction

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 + O 2  CaO synthesis or decomposition? Synthesis Chemical Reaction Balanced equation 2Ca + O 2  2CaO Balanced chemical equation 2Ca (s) + O 2(g)  2CaO (s)

copper(II) oxide  copper + oxygen gas skeleton equation: CuO  Cu + O 2 synthesis or decomposition? Decomposition Chemical Reaction Balanced equation 2CuO  2Cu + O 2 Balanced chemical equation 2CuO (s)  2Cu (s) + O 2(g)

More work/ Homework Page 185 # 1 to 6 and Page 189 #1 to 5