Entropy and Free Energy 18.4

Spontaneous Reactions Produce substantial amounts of products at equilibrium and release free energy. Free energy is energy that is available to do work, such as propelling a car. Nonspontaneous reactions do not favor the formation of the products at specified conditions. Changing factors such as temperature, pressure, or coupled reactions can make a nonspontaneous reaction spontaneous. Ex: H2CO3 (aq) CO2 (g) + H2O (l) <1% >99%

Entropy Entropy is the measure of the disorder of a system. Law of Disorder: the natural tendency is for systems to move in the direction of maximum disorder or randomness. Entropy Increase = Spontaneous Reaction Ex: Solid to liquid to gas phase changes, dissolving a crystalline solid (breaking compound into its ions), and raising temperature. Entropy Decrease = Nonspontaneous Reaction *Refer to table 18.3 for further reference

Gibbs Free Energy Gibbs free-energy change: the maximum amount of energy that can be coupled to another process to do useful work. ΔG = ΔH – TΔS Either enthalpy or entropy, but not both, can be unfavorable for a spontaneous reaction. ΔG is negative for spontaneous reactions because the system loses free energy.