Thermodynamics, Kinetics & Equilibrium

Energy is conserved: the change in internal energy equals heat added to the system plus work done on it, ΔU = q + w. Energy is neither created nor destroyed.

Enthalpy is heat content at constant pressure. ΔH is the heat absorbed or released by a reaction at constant pressure.

Exothermic reactions release heat (ΔH < 0); endothermic reactions absorb heat (ΔH > 0).

The enthalpy change of an overall reaction equals the sum of the enthalpy changes of its steps, because ΔH is a state function (path-independent).

ΔHf° is the enthalpy change to form one mole of a compound from its elements in standard states. It is zero for an element in its standard state.

ΔH°rxn = Σ ΔHf°(products) − Σ ΔHf°(reactants), each weighted by stoichiometric coefficients.