To determine the changes that occur when the temperature of the system described by the equation
[tex]\[
N_2(g) + 3 H_2(g) \leftrightarrow 2 NH_3(g) + \text{energy}
\][/tex]
is decreased, we need to consider how equilibrium is affected by changes in temperature according to Le Chatelier's principle.
1. Understanding the Reaction:
The chemical equilibrium reaction is:
[tex]\[
N_2(g) + 3 H_2(g) \leftrightarrow 2 NH_3(g) + \text{energy}
\][/tex]
This reaction is exothermic, which means it releases energy in the form of heat as it proceeds in the forward direction (towards the formation of [tex]$NH_3$[/tex]).
2. Le Chatelier's Principle:
Le Chatelier's principle states that if an external change is applied to a system at equilibrium, the system will adjust itself to counteract that change. Specifically, for temperature changes:
- If the temperature is increased, the equilibrium will shift towards the endothermic direction (the direction that absorbs heat) to counteract the added heat.
- Conversely, if the temperature is decreased, the equilibrium will shift towards the exothermic direction (the direction that releases heat) to counteract the loss of heat.
3. Applying the Principle:
In this case, since the forward reaction (formation of [tex]$NH_3$[/tex]) is exothermic and releases energy, decreasing the temperature would cause the equilibrium to shift towards the formation of more [tex]$NH_3$[/tex]. The system will do this in an effort to release more heat and counteract the temperature decrease.
4. Effect on Concentrations:
- The concentration of [tex]$NH_3(g)$[/tex] will increase because the equilibrium shifts toward the product side to produce more [tex]$NH_3$[/tex].
- As a result, the reactants [tex]$(N_2(g) \text{ and } H_2(g))$[/tex] will be consumed to form more [tex]$NH_3$[/tex].
- Thus, the concentration of [tex]$H_2(g)$[/tex] will decrease.
Given the changes described:
- The concentration of [tex]$H_2(g)$[/tex] decreases.
- The concentration of [tex]$NH_3(g)$[/tex] increases.
Therefore, the correct answer is:
D) The concentration of [tex]$H_2(g)$[/tex] decreases and the concentration of [tex]$NH_3(g)$[/tex] increases.
