Question

A reaction chamber contains a mixture of \(\mathrm{N}_{2}\) and \(\mathrm{N}\) in equilibrium at a specified temperature and pressure. How will ( \(a\) ) increasing the temperature at constant pressure and (b) increasing the pressure at constant temperature affect the number of moles of \(\mathrm{N}_{2} ?\)

Short answer

Answer: (a) When the temperature is increased at constant pressure, the number of moles of N₂ will decrease. (b) When the pressure is increased at constant temperature, the number of moles of N₂ will increase.

Step-by-step solution

The equilibrium reaction

First, we need to write the equation representing the equilibrium between N₂ and N. The dissociation of N₂ can be represented as: N₂ (g) ⇌ 2N (g)

Applying Le Chatelier's principle

Le Chatelier's principle states that if a system at equilibrium is subjected to a change in temperature, pressure, or concentration, the system will adjust itself to counteract the effect of the change and establish a new equilibrium. We will use this principle to analyze the effects of the changes in temperature and pressure.

Effect of increasing temperature at constant pressure (a)

For the given reaction, we know that the dissociation of N₂ into N is an endothermic process. When the temperature is increased, the equilibrium will shift in the direction that absorbs the excess heat. In this case, that means the equilibrium will shift towards the right (towards the production of more N). As a result, the number of moles of N₂ will decrease.

Effect of increasing pressure at constant temperature (b)

For analyzing the effect of pressure, we need to see the number of moles of gas on both sides of the equilibrium equation. In this case: N₂ (g) ⇌ 2N (g) Since there are 2 moles of gas on the right side and 1 mole on the left side, the equilibrium will shift towards the side with fewer moles of gas to counteract the increased pressure. Thus, the equilibrium will shift towards the left (towards the production of more N₂). As a result, the number of moles of N₂ will increase with an increase in pressure at constant temperature.