⚗️ Chemical Equilibrium
Explore how temperature, enthalpy, entropy and initial concentrations determine whether a reaction “goes”. Watch the Gibbs free energy G(Q) curve find its minimum at equilibrium, animate ICE concentration bars, and verify Le Châtelier’s principle live.
Thermodynamics
Stoichiometry & conc.
Equilibrium results
Chemical Equilibrium Theory
Gibbs Free Energy & Equilibrium
At constant T and p the reaction quotient Q evolves until ΔrG = ΔrG° + RT ln Q = 0, i.e. Q = K. The G(Q) curve has a minimum exactly at K. For Q < K the reaction proceeds forwards (ΔrG < 0); for Q > K it reverses. K = exp(−ΔG°/RT) quantifies how far a reaction lies to the right at equilibrium.
Le Châtelier’s Principle
If a system at equilibrium is perturbed (add/remove reactant or product, change T or p), it shifts to counteract the change. Increasing T favours the endothermic direction (shifts K). Increasing total pressure favours the side with fewer moles of gas (Δn = c + d − a − b for all-gas reactions). Adding inert gas at constant volume does not shift equilibrium.
van’t Hoff Equation
d ln K / dT = ΔH° / RT². Integrating: ln(K2/K1) = −ΔH°/R · (1/T2 − 1/T1). A plot of ln K vs 1/T is linear with slope −ΔH°/R, allowing enthalpy extraction from temperature-dependent equilibrium data — widely used in enzyme kinetics (pH-stat calorimetry) and industrial reactor design.
Kp and Kc
For gas-phase reactions Kp uses partial pressures (bar) and Kc uses molar concentrations (mol/L). Kp = Kc(RT)Δn where Δn = Σνproducts − Σνreactants. For reactions with equal numbers of gas moles (Δn = 0) the two are identical. The Haber process for NH3 synthesis has Δn = −2, making high pressure favour the product side.