Question

The yield of \(\mathrm{NH}_{3}\) in the reaction \(\mathrm{N}_{2}+3 \mathrm{H}_{2} \rightleftharpoons 2 \mathrm{NH}_{3}\) \(\mathbf{A H}=-22.08\) keal is affected by (a) change in pressure and temperature (b) change in temperature and concentration of \(\mathrm{N}_{2}\) (c) change in pressure and concentration of \(\mathrm{N}_{2}\) (d) change in pressure, temperature and concentration of \(\mathrm{N}_{2}\).

Short answer

The yield of NH3 is affected by changes in pressure, temperature, and concentration of N2; therefore, all options (a, b, c, d) are correct.

Step-by-step solution

Understand the Concept of Le Chatelier's Principle

This principle states that if an external condition (pressure, temperature, or concentration) is changed, the equilibrium position will shift to counteract the imposed change and try to re-establish equilibrium.

Assess the Impact of Pressure Change

Increasing the pressure of the system by decreasing the volume will shift the equilibrium towards the side with fewer moles of gas to minimize the change. In the reaction presented, the production of NH3 from N2 and H2 results in a decrease in the number of moles (from 4 moles of reactants to 2 moles of products). Thus, an increase in pressure would favor the formation of NH3.

Assess the Impact of Temperature Change

The negative \(\mathbf{AH}\) value indicates the reaction is exothermic. According to Le Chatelier's Principle, increasing the temperature will favor the endothermic direction (reverse reaction here) since the system will try to absorb the extra heat. Conversely, decreasing the temperature favors the exothermic direction (forward reaction), increasing the yield of NH3.

Assess the Impact of Changes in N2 Concentration

Increasing the concentration of one of the reactants (N2 in this case) will shift the equilibrium towards the right to form more products (NH3). Decreasing the concentration has the opposite effect.

Combine the Effects for the Final Answer

The yield of NH3 can be affected by all the factors listed: change in pressure (a and c), temperature (a, b, and d), and concentration of N2 (b, c, and d). Thus, each of the provided options has a bearing on the reaction equilibrium and can affect the yield of NH3.

Key concepts

Understanding Chemical Equilibrium

In chemistry, chemical equilibrium occurs in a reversible reaction when the rate of the forward reaction equals the rate of the reverse reaction and the concentrations of reactants and products remain constant over time. It's a state of dynamic balance where chemical processes occur at the same rate in both directions.

Consider the synthesis of ammonia (\textbf{NH}\(_3\)), which can be represented by the equation \textbf{N}\(_2\) + 3\textbf{H}\(_2\) \(\rightleftharpoons\) 2\textbf{NH}\(_3\). At equilibrium, the system is at a state where the concentration of \textbf{N}\(_2\), \textbf{H}\(_2\), and \textbf{NH}\(_3\) does not change despite continuous chemical processes. It's important to note that equilibrium doesn't mean the reactants and products are present in equal amounts, but that their ratios are constant.

Effect of Pressure on Equilibrium

The effect of pressure on equilibrium is based on Le Chatelier's Principle, which suggests that if a system at equilibrium experiences a change in pressure, the system will adjust itself to counter that change. In reactions involving gases, increasing pressure by decreasing volume will shift the equilibrium toward the side with fewer moles of gas.

In the case of ammonia synthesis, there are 4 moles of gas as reactants (\textbf{N}\(_2\) and \textbf{H}\(_2\)) and 2 moles of gas as the product (\textbf{NH}\(_3\)). Consequently, an increase in pressure will shift the equilibrium to the right, favoring the production of ammonia to reduce the pressure by having fewer moles of gas.

Effect of Temperature on Equilibrium

Understanding Exothermic Reactions

When it comes to effect of temperature on equilibrium, Le Chatelier's Principle offers a clear guideline: if you increase the temperature, the system will favor the endothermic reaction, which consumes heat. Conversely, decreasing the temperature will shift the balance towards the exothermic reaction, which releases heat.

Since the synthesis of ammonia is an exothermic process (\textbf{AH} is negative), raising the temperature would shift the equilibrium towards the decomposition of \textbf{NH}\(_3\), reducing the yield of ammonia. Lowering the temperature, conversely, would promote the formation of \textbf{NH}\(_3\), hence increasing its yield.

Influence of Concentration on Equilibrium

Lastly, the influence of concentration on equilibrium is another fundamental aspect of Le Chatelier's Principle. When the concentration of a reactant or product in a reaction at equilibrium is changed, the system will shift in a way that 'consumes' the added substance or 'replenishes' the removed one.

Applying this to our ammonia synthesis example, if the concentration of \textbf{N}\(_2\) is increased, the equilibrium will shift to the right, leading to more \textbf{NH}\(_3\) being produced. Conversely, if the concentration of \textbf{NH}\(_3\) were to be increased, the system would shift to the left, favoring the reactants (\textbf{N}\(_2\) and \textbf{H}\(_2\)). This dynamic adjustment allows the system to maintain equilibrium under altered concentrations.