The reaction quotient Q can be used to predict the directionality of a chemical reaction when compared to the equilibrium constant Kc.

It is calculated similarly to Kc. However, the concentration of products and reactants are taken at any point in time t while the reaction is NOT in equilibrium.

The first equation is the general chemical reaction equation in an equilibrium state, where the reactants (A and B) are on the left side and the products (C and D) are on the right side. The equilibrium state is indicated by a double arrow. The second equation is the reaction quotient equation - Q, which is equal to multiplication of the product’s concentrations raised to the power of their coefficients, divided by multiplication of the reactant’s concentrations raised to the power of their coefficients at the current time. When the value of Q is higher than the value of Kc, the reaction forms reactants, when it is lower, the reaction forms products, whereas when Q is equal to Kc, the reaction is in equilibrium.