Solution
= Solution
At fixed temperature and pressure, <thermochemical equilibrium> minimizes the <Gibbs free energy> subject to elemental conservation. For every independent reaction with stoichiometric coefficients $\nu_i$,
$$
\boxed{\Delta_rG=\sum_i\nu_i\mu_i=0}.
$$
Equivalently, forward and reverse rates satisfy detailed balance. For ideal gases,
$$
\boxed{\prod_i\left(\frac{p_i}{p^\circ}\right)^{\nu_i}
=K_p(T)=\exp\left[-\frac{\Delta_rG^\circ(T)}{RT}\right]}.
$$