Question

For each of the following systems at equilibrium, predict whether the reaction will shift to the right, left, or not be affected by an increase in temperature. (a) \(2 \mathrm{H}_{2} \mathrm{O}_{2}(g) \rightleftharpoons 2 \mathrm{H}_{2} \mathrm{O}(g)+\mathrm{O}_{2}(g)\) exothermic (b) \(\mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) \Longrightarrow 2 \mathrm{NO}(g)\) endothermic

Short answer

For part (a), an increase in temperature shifts the reaction to the left. For part (b), an increase in temperature shifts the reaction to the right.

Step-by-step solution

- Evaluate the exothermic reaction

In the exothermic reaction \[2 H_2O_2(g) \rightleftharpoons 2 H_2O(g)+O_2(g)\], the system releases heat. Therefore, an increase in temperature will shift the reaction to the left, towards the reactants side.

- Evaluate the endothermic reaction

Regarding the endothermic reaction \[N_2(g)+O_2(g) \Longrightarrow 2 NO(g)\], the system absorbs heat. Thus, an increase in temperature will shift the reaction to the right, towards the products side.

Key concepts

Exothermic Reaction

An exothermic reaction is a type of chemical process where energy, usually in the form of heat, is released into the surroundings. When a reaction releases energy, it typically means that the energy required to break the bonds of the reactants is greater than the energy involved in forming the bonds of the products. This excess energy is given off as heat.
In terms of chemical equilibrium, when the temperature is increased for an exothermic reaction, the system responds by attempting to absorb the extra heat. According to Le Chatelier's Principle, the reaction will shift to the left, towards the side with the reactants, trying to counterbalance the added heat. This is because the forward reaction releases heat, so by shifting left, the reaction absorbs some of the excess heat introduced. In practical terms, an exothermic reaction will favor the formation of reactants if the temperature rises, meaning the equilibrium shifts to oppose the change.

Endothermic Reaction

Endothermic reactions are the opposite of exothermic reactions. In endothermic processes, the reaction absorbs energy, typically heat, from the surroundings. This means the energy required to break the bonds of the reactants is lower than the energy needed to form the bonds of the products.
When analyzing chemical equilibrium in an endothermic reaction, an increase in temperature will have the opposite effect compared to exothermic reactions. The system seeks to absorb the added heat, causing the equilibrium to shift to the right toward the products side. By moving right, the process capitalizes on the extra heat to facilitate the forward reaction, essential in endothermic pathways. So, with more heat, the formation of products is favored, effectively counteracting the temperature change by enhancing the heat absorption process.

Chemical Equilibrium

Chemical equilibrium occurs in a reversible reaction when the rate of the forward reaction equals the rate of the reverse reaction. At this point, the concentrations of the reactants and products become constant, although they are not necessarily equal.
Le Chatelier's Principle helps predict how a system at equilibrium will respond to disturbances or changes in conditions like temperature, pressure, or concentration. For example:

• If the temperature increases in an exothermic reaction, the system shifts left to absorb the extra heat, resulting in more reactants.
• If the temperature increases in an endothermic reaction, the system shifts right, favoring the products.

These shifts demonstrate the dynamic nature of equilibrium as systems strive to minimize the effect of changes imposed on them. Understanding how equilibrium adjusts helps in optimizing reactions in industrial applications, such as the production of chemicals like ammonia and sulfuric acid.