Chapter 8. Thermochemistry

First law of thermodynamics: ΔU = q + w. Enthalpy H = U + PV; at constant pressure, ΔH = q_p [4].

Exothermic: ΔH < 0. Endothermic: ΔH > 0.

Calorimetry: q = mcΔT.

Hess’s law: ΔH is path independent, so ΔH_rxn = ΣΔH_f°(products) − ΣΔH_f°(reactants).

Second law and entropy. Entropy (S) measures dispersal of energy or microstates. Gibbs free energy: ΔG = ΔH − TΔS. A reaction is spontaneous when ΔG < 0. Also ΔG° = −RT ln K [4].

Review: Why is melting ice spontaneous above 0 °C?