# How will this system respond to a temperature increase?

Consider this system at equilibrium

A(aq) + heat <==> B(aq) …………… ΔH = +450 kJ/mol

K = [B] / [A]

Q is the “reaction quotient” and is used to determine which way a given system will move to establish equilibrium. If the initial conditions give a Q which is larger than K, then the equilibrium will move to the left to establish equilibrium. If the value of Q is less than the value of K, then the system will move to the right to establish equilibrium. If Q happens to equal K, then the system is at equilibrium.

When we have a system at equilibrium, then Q = K. A change will affect the value of Q. In this case a temperature change will cause an increase in [B] and a decrease in [A], producing an increase in Q, followed by a shift to the right. When equilibrium is re-established, there will be more B than there was originally and less A since the equilibrium has shifted to the right to use up the added heat according to Le Chatelier’s principle.

When equilibrium is re-established the value of K will be greater. Temperature changes are the only changes that actually change the value of K.