Compute the reaction quotient Q from species concentrations or partial pressures to compare with K.
输入反应物与生成物的浓度及系数，求反应商 Q 并与 K 比较。
| Item | Formula / Note | Source / Standard |
|---|---|---|
| Reaction quotient | Q = product of a_i^nu_i, products over reactants raised to stoichiometric powers | IUPAC, Compendium of Chemical Terminology (Gold Book) |
| Direction criterion | Q < K proceeds forward; Q = K at equilibrium; Q > K proceeds in reverse | Atkins PW, de Paula J, Physical Chemistry, Oxford Univ. Press |
| Relation to Gibbs energy | ΔG = ΔG° + R · T · ln Q = R · T · ln( Q/K ) | Atkins PW, de Paula J, Physical Chemistry |
| Activity approximation | In dilute solutions the activity is often approximated by concentration over the standard concentration | IUPAC, Compendium of Chemical Terminology (Gold Book) |