Question

nitrogen and oxygen react to form nitrogen monoxide, like this:

n₂(g)+o₂(g)→2no(g)

the reaction is endothermic. suppose a mixture of n₂, o₂ and no has come to equilibrium in a closed reaction vessel. predict what change, if any, the perturbations in the table below will cause in the composition of the mixture in the vessel. also decide whether the equilibrium shifts to the right or left.

Explanation:

Step1: Le - Chatelier's principle for temperature change in endothermic reactions

For an endothermic reaction \(N_{2}(g)+O_{2}(g)
ightleftharpoons2NO(g)\), heat is absorbed in the forward reaction (\(\Delta H> 0\)). When the temperature is lowered, according to Le - Chatelier's principle, the system will try to counteract the change. Since the forward reaction is endothermic (absorbs heat), the reverse reaction (which is exothermic) will be favored. The reverse reaction \(2NO(g)
ightarrow N_{2}(g)+O_{2}(g)\) consumes \(NO\) and produces \(N_{2}\) and \(O_{2}\). So, the pressure of \(O_{2}\) will increase. And the equilibrium shifts to the left.

Step2: Le - Chatelier's principle for temperature increase in endothermic reactions

When the temperature is raised, the system will try to absorb the added heat. Since the forward reaction \(N_{2}(g)+O_{2}(g)
ightarrow2NO(g)\) is endothermic (absorbs heat), the forward reaction will be favored. As the forward reaction proceeds, more \(NO\) is produced. So, the pressure of \(NO\) will increase. And the equilibrium shifts to the right.

Answer:

• When the temperature is lowered: The pressure of \(O_{2}\) will increase, and the equilibrium shifts to the left.
• When the temperature is raised: The pressure of \(NO\) will increase, and the equilibrium shifts to the right.