Chapter 6 Chemical Reactions Section 1 The Nature of Chemical Reactions p. 184

Compare exothermic and endothermic reactions Objectives Compare exothermic and endothermic reactions Analyze how a reaction takes place

Are you able to predict your parent’s reactions? How do you know? Think…. Are you able to predict your parent’s reactions? How do you know?

I. Chemical reactions change substances – it rearranges atoms 25 O2 + 2 C8H18  16 CO2 + 18 H2O Products Reactants Yields

II. Energy and Reaction Activation Energy – energy amount needed to start a reaction A. Energy is needed to break bonds (heat, electricity, sound, light, etc) B. Forming bonds releases energy (sometimes as heat or light) C. Energy is conserved – chemical energy – energy is released when a chemical compound reacts to produce new compounds

1. Exothermic – reaction where thermal energy is released (heat) Products have less energy than reactants Time Energy

2. Endothermic – reaction that absorbs thermal energy Products have more energy than reactants Energy Time