Question

Hydrogen gas and chlorine gas in the presence of light react explosively to form hydrogen chloride $$ \mathrm{H}_{2}(g)+\mathrm{Cl}_{2}(g) \rightleftharpoons 2 \mathrm{HCl}(g) $$ The reaction is strongly exothermic. Would an increase in temperature for the system tend to favor or disfavor the production of hydrogen chloride?

Short answer

Increasing the temperature of the system would disfavor the production of hydrogen chloride, as it would cause the equilibrium to shift towards the endothermic direction (reverse reaction) according to Le Chatelier's principle. This is because the given reaction is exothermic and releases heat, making heat a "product" in this reaction.

Step-by-step solution

Identify the reaction and the type of reaction.

The given reaction is: \[ \mathrm{H}_{2}(g)+\mathrm{Cl}_{2}(g) \rightleftharpoons 2 \mathrm{HCl}(g) \] This is an exothermic reaction (it releases heat), as mentioned in the problem.

Apply Le Chatelier's principle to analyze the effect of temperature.

In this reaction, heat can be considered as a "product" since it is an exothermic reaction. According to Le Chatelier's principle, increasing the temperature of the system will cause the equilibrium to shift in the direction that consumes more heat, which is the endothermic direction, or the reverse reaction.

Determine the impact of increasing temperature on the production of hydrogen chloride.

In our case, the exothermic reaction (forward reaction) produces hydrogen chloride, while the endothermic reaction (reverse reaction) consumes it. Since increasing temperature will cause the equilibrium to shift towards the endothermic direction, it would tend to disfavor the production of hydrogen chloride. Therefore, increasing the temperature of the system would disfavor the production of hydrogen chloride.

Key concepts

Equilibrium Shift

Understanding the concept of equilibrium shift is essential when analyzing how a chemical system responds to changes. In the context of chemical reactions, equilibrium is the point where the reactants and products are formed at the same rate. This balance can be disrupted by changing certain conditions, such as concentration, pressure, or temperature.
A shift in equilibrium refers to the system's adjustment to reestablish equilibrium after a change. Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change and restore balance.
For instance, in the reaction of hydrogen gas and chlorine gas to form hydrogen chloride, the equilibrium can shift to favor either the forward or reverse reaction based on external manipulation, such as temperature changes. Understanding how these shifts occur can help predict how much of a product or reactant will be present at equilibrium.

Exothermic Reaction

Exothermic reactions are chemical processes that release energy in the form of heat. These reactions result in the surrounding environment becoming warmer. This release of energy happens when the products of the reaction have lower energy than the reactants.
In the reaction between hydrogen gas and chlorine gas to form hydrogen chloride, energy is released as the chemical bonds in the products are more stable than those in the reactants. This makes it an exothermic process. A good way to recognize an exothermic reaction is by noting that it can often proceed on its own once the initial energy barrier is overcome.
When analyzing an exothermic reaction, it’s crucial to see heat as a product. Changes in the system that affect temperature can influence the rate and direction of such reactions. This interaction between the exothermic nature of the reaction and external influences like temperature regulation can dictate the amount of product formed.

Temperature Effect on Reactions

Temperature significantly impacts the direction and extent to which a reaction proceeds. For exothermic reactions, like the formation of hydrogen chloride from hydrogen and chlorine gases, an increase in temperature causes an intriguing shift in equilibrium.
According to Le Chatelier's Principle, increasing the temperature of an exothermic reaction adds heat to the system, effectively increasing the concentration of a product (heat). To counter this and restore equilibrium, the system shifts towards the absorbent process, which is the endothermic reaction or the reverse direction. This shift results in decreased production of the exothermic reaction's products.

Thus, increasing the temperature in an exothermic reaction system might disfavor product formation, as the equilibrium moves to balance the added heat by favoring reactants. It's a fascinating demonstration of how delicate the balance in chemical systems can be and highlights the importance of controlling environmental conditions to drive reactions in the desired direction.