2. Heat Transfer Heat energy is caused by random motion and collision of particles. Heat is measured in joules or calories. Heat cannot be created or destroyed, but it can flow between objects. Heat flows from hotter (higher energy) objects to colder (lower energy) objects. Examples Which way will heat energy flow?

3. Endothermic reactions Chemical reactions that absorb energy. The products have a higher energy than the reactants. Endothermic reactions in a beaker or other container will feel cold. Examples of endothermic reactions. Ice melting into liquid water Cooking an egg N 2 + O 2 + 93.0 kJ ---> 2NO

4. Exothermic Reactions Chemical reactions that release energy. The products have a lower energy than the reactants. Exothermic reactions in a beaker or other container will feel hot. Examples of exothermic reactions. Liquid water freezing into ice. C 3 H 8 + 5O 2  3CO 2 + 4H 2 O + 48.0 kJ

5. Entropy Tendency towards a state of increased disorder. Reactions that occur spontaneously are usually the ones that are accompanied by an increase in entropy. Ice melting into liquid water occurs spontaneously, even though energy has to be absorbed, because the molecules themselves are becoming less ordered.