Keq vs. Q Period 2 Sandra

When do you do this? Keq - Is used to provide information about the mixture of reactants and products at equilibrium. Q – Is use to determine if a reaction is at equilibrium

Definitions Keq - The ratio depicting the concentrations when chemical equilibrium is reached and express the extent to which equilibrium has favored in either direction. Q – Determines if the reaction is at equilibrium.

Rules/Steps To determine if a reaction is at equilibrium, you need to calculate the reaction quotient(Q) and compare it to the equilibrium constant. You use the concentrations that the problem provides. Set it up just as you would set up a Keq expression. Q=product/reactant Solve Look at the answer and determine whether the reaction is at equilibrium. To determine if the reaction is at equilibrium Keq has to equal Q.

Example COCl2 ↔ CO + Cl2 Keq = 170 Concentrations: CO and Cl2 are each 0.15M and COCl2 is 1.1 * .001 Q = [CO] [Cl2] / [COCl2] Q = (0.15)(0.15) / (1.1 * .001) = 20 Q < Keq thus the reaction is not at equilibrium and proceeds to the right.

Example Problem N2 + 3H2 ↔ 2NH3 NH3 = 0.15M N2 = 0.0020M H2=.10M

Answer Keq = [Nh3]2