thermodynamics

First Law of Thermodynamics

Energy cannot be created or destroyed. ΔU = q + w.

q in thermodynamics

Heat transferred into or out of the system.

w in thermodynamics

Work done on or by the system.

Enthalpy (H)

Heat content at constant pressure: H = U + PV.

Entropy (S)

A measure of disorder or randomness.

Second Law of Thermodynamics

The total entropy of the universe always increases for a spontaneous process.

Gibbs Free Energy

G = H - TS, determines spontaneity.

ΔG < 0

The reaction is spontaneous.

ΔG = 0

The system is at equilibrium.

Heat transfer formula (no phase change)

q = mcΔT.

Hess’s Law

The total enthalpy change of a reaction is the sum of the changes for individual steps.

Sign of ΔH in an exothermic reaction

Negative.

Unit of entropy (S)

J/mol·K.

Positive ΔS

Increased disorder.

Phase change

Occurs when temperature remains constant while heat is added or removed.