Question

A chemistry student needs to determine the effect of decreasing the temperature on the equilibrium position of the reaction N2(g) + 3H2(g) <-> 2NH3(g) if the initial concentrations of N2, H2 and NH3 are 0.4 M, 0.6 M, and 0.8 M respectively. How does the equilibrium concentration of NH3 change if the temperature is decreased from 400 K to 300 K, assuming constant volume and pressure?

Answer 1

To determine the effect of decreasing the temperature on the equilibrium position of the reaction, we need to consider the reaction's enthalpy change and Le Chatelier's principle.The reaction N2 g  + 3H2 g  <-> 2NH3 g  is exothermic, meaning it releases heat when it proceeds in the forward direction. According to Le Chatelier's principle, if an external stress is applied to a system at equilibrium, the system will adjust itself to minimize the effect of the stress.In this case, the stress applied to the system is a decrease in temperature from 400 K to 300 K. Since the reaction is exothermic, decreasing the temperature will cause the system to shift towards the side that generates heat, which is the forward direction  formation of NH3 . This means that the equilibrium concentration of NH3 will increase.However, without the equilibrium constant  K  or the enthalpy change  H  for the reaction, we cannot provide a quantitative answer for how much the equilibrium concentration of NH3 will change.