Chemistry 102: Equilibrium: Find Equilibrium constant based off images/time.

Question

The progress with time of a reaction system is depicted in the figure here. Red spheres represent the molar concentration of substance A, and blue spheres represent the molar concentration of substance B.

What is the value of the equilibrium constant K_c?

Answer 1

First, let us write the reaction equation

A ⇔ B

Next, let us write the expression for the equilibrium constant

K_C = [B]_eq / [A]_eq

Next, let us count the red and the blue spheres on the rightmost picture. There are 16 red spheres (A) and 24 blue spheres (B). Their ratio is 24/16 = 1.5

Finally we need to confirm that the system in the rightmost frame reached equilibrium. In order to do it we need to determine the B to A ratio in the previous frame (second from the right). It also contains 16 red spheres and 24 blue spheres, same as in the last image. The ratio being unchanged means that the system reached equilibrium.

Hence K_C = [B]_eq / [A]_eq = 1.5