7.1: Energy and Chemical Bonds Energy is the ability to do work. Heat is the transfer of energy due to temperature differences. Energy and heat are expressed in units of joules. 7.2: Heat Changes during Chemical Reactions Heat transfer is related to temperature change. Heat is equal to the product of the mass, the change in temperature, and a proportionality constant called the specific heat. 7.3: Exothermic and Endothermic Reactions Atoms are held together by a certain amount of energy called bond energy. Chemical processes are labeled as exothermic or endothermic based on whether they give off or absorb energy, respectively. 7.4: Why Do Chemical Reactions Occur? Free Energy One of the major goals of chemical thermodynamics is to establish criteria for predicting whether a particular reaction or process will occur spontaneously. We have developed one such criterion, the change in entropy of the universe. This is not particularly useful and a criterion of spontaneity that is based solely on the state functions of a system would be much more convenient and is provided by a new state function: the Gibbs free energy. 7.5: How Do Chemical Reactions Occur? Reaction Rates 7.6: Effects of Temperature, Concentration, and Catalysts on Reaction Rates 7.7: Reversible Reactions and Chemical Equilibrium 7.8: Le Chatelier’s Principle- The Effect of Changing Conditions on Equilibria This page looks at Le Châtelier's Principle and explains how to apply it to reactions in a state of dynamic equilibrium. It covers changes to the position of equilibrium if you change concentration, pressure or temperature. It also explains very briefly why catalysts have no effect on the position of equilibrium.