CHEM 131 - Ch10 Entropy...

Enthalpy Driven

Description of a process change in H and change in S are both negative and which is spontaneous only at low temperatures.

Entropy (S)

A state function that measures the dispersal of energy in a system. Entropy is correlated with the degree of randomness or disorder of a system on the molecular level.

Entropy Driven

Description of a process for which change in H and change in S are both positive and which is spontaneous only at high temperatures.

Gibbs Free Energy (G)

A thermodynamic state function that can be used to predict the direction of spontaneous change at constant temperature and pressure. Change in G = Change in H - T (change in S), and if the change in G is less than 0, it’s a spontaneous process.

Irreversible Change

Description of a process, often far from equilibrium, which cannot be reversed by a small incremental change in any variable.

Microstate

One possible way for a collection of particles to assume a given total energy.

Reversible Change

Description of a process near equilibrium, which can be reversed by a small incremental change of some variable.

Second Law of Thermodynamics

The entropy of the universe is constantly increasing. For any spontaneous process, the change in S of the universe is greater than 0.

Spontaneous Process

Any thermodynamic process that takes place without continuous intervention. Note that being spontaneous does not necessarily mean that a process will be fast.

Standard Gibbs Free Energy Change, Change in G^o

Free energy change for a reaction in which all participating substances are present in their thermodynamic standard state (gases at 1 atm, solutions at 1 M, T = 25 C). See also Gibbs free energy.

Standard Molar Entropy (S^o)

Absolute entropy of 1 mole of a substance at 25 C.

Third Law of Thermodynamics

The entropy of a perfect crystal of any pure substance approaches zero as the temperature approaches absolute zero.