Applications of K and the reaction quotient

The size of K shows how far a reaction goes: K > 10³ means products dominate, K < 10⁻³ means reactants dominate, and values in between mean appreciable amounts of both.

The reaction quotient Q has the same form as K but uses concentrations at any instant, not just at equilibrium.

If Q < K the reaction moves forward; if Q > K it moves backward; if Q = K it is at equilibrium.

To calculate equilibrium amounts, set up an initial-change-equilibrium table using the stoichiometry, substitute into K and solve.

Equilibrium concentrations depend on starting conditions, but the ratio defined by K does not.