Le Chatelier’s Principle and Chemical Equilibrium

Question

The oxidation of NO to NO₂ is exothermic.

2 NO(g) + O₂(g) -----> 2 NO₂(g)

If the system is at equilibrium and the temperature is increased, will the concentration of NO increase, remain the same or decrease? Explain why.

Answer 1

Exothermic reactions mean that heat is being released. If heat is being released in a reaction, that means it will be a product. So you are adding something to the right side of the reaction.

Think about a balance. If one side is heavier than the other, and you want to reach equilibrium, you have to add something to the other side to make it balanced.

Therefore, since there are more compounds on the RIGHT side the equilibrium is shifted to the opposite side, left side, and you need to add to the LEFT side to achieve equilibrium. That is why the concentration of NO will be INCREASED.

Answer 2

In an exothermic reaction heat is a product, so if we add a product then equilibrium shifts left and [NO] increases