= Chemical thermodynamics
{wiki}
<Chemical thermodynamics> studies energy, entropy, and equilibrium in chemical systems. At fixed temperature and pressure, the direction of spontaneous change is constrained by <Gibbs free energy>, and equilibrium corresponds to an appropriate minimum subject to the system's conserved quantities.
For a reaction, $\Delta_rG=\Delta_rG^\circ+RT\ln Q$, where $Q$ is the reaction quotient. Setting $\Delta_rG=0$ gives $K=\exp(-\Delta_rG^\circ/RT)$ for the dimensionless equilibrium constant. This connects measurable composition with free energy. It does not determine the reaction rate, which also depends on the accessible pathway and its activation barriers.
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