Enthalpy Nature is lazy Nature loves decreases in heat Nature loves -ΔH Exothermic reactions are favored

Entropy Entropy is a measure of disorder The symbol of entropy is S Nature loves disorder The symbol of entropy is S We can’t measure entropy we measure change in entropy Δ S Nature loves + Δ S

Entropy Entropy is a hard concept to understand It is the partitioning of energy among all possible energy levels of a system Even among things that may not seem to be energy related Sometimes can and do contribute to entropy! The best idea: Think of an increase in Entropy as an increase in disorder.

Phase change Entropy increases as a substance changes from a solid to a liquid and from a liquid to a gas.

Dissolving (gas into liquid or solid) Gas particles have more entropy when they can move freely than when they are dissolved in a liquid or solid that limits their movements and randomness.

Number of particles product vs reactants Assuming no change in physical state occurs, the entropy of a system usually increases when the number of gaseous product particles is greater than the number of gaseous reactant particles.

Dissolving (solid or liquid into solvent) With some exceptions, entropy increases when a solid or a liquid dissolves in a solvent.

Temperature The random motion of the particles of a substance increases as its temperature increases.

Combinations Two mols of two types of molecules, one Mol each have greater entropy than two mols of one type of molecule.

Guidelines Entropy increases with T Entropy is highest for gases, lowest for solids Gas expansion increases entropy Mixing increases entropy

Gibbs Gibbs Energy Also known as Gibbs Free Energy or just Free Energy The latter is not desirable because there is another quantity called Helmholtz Free Energy Gibbs Energy is suitable for predicting spontaneity in constant pressure reactions

Gibbs Energy G = ΔH - TΔS Takes into account the effects of Enthalpy Entropy Temperature In one neat (elegant) equation