Look at the three graphs below, which show how K_c for an equilibrium is affected by various changes.

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Which graph shows the effect of increasing temperature of an equilibrium that has an endothermic forward reaction?

Graph C, because K_c is larger at higher temperatures.

How can you tell that graph B shows the effect of adding a catalyst to the reaction?

Because K_c remains constant and a catalyst has no effect on K_c.

What can you tell from graph A about the back reaction of the equilibrium if the horizontal axis represents temperature?

K _c decreases with temperature so the forward reaction must be exothermic. This means that the back reaction must be endothermic.