Question

Hydrogen and fluorine react to form \(\mathrm{HF}\) according to the following equilibrium equation. \(\mathrm{H}_{2}(\mathrm{g})+\mathrm{F}_{2}(\mathrm{g}) \rightleftharpoons 2 \mathrm{HF} \Delta H=-538 \mathrm{kJ}(\mathrm{g})\) Will raising the temperature cause the amount of product to increase? Explain. (Chapter 17\()\)

Short answer

Raising the temperature in the given chemical equilibrium system will not cause the amount of product (\(\mathrm{HF}\)) to increase. Since the reaction is exothermic (\(\Delta H = -538 \mathrm{ kJ}\)), increasing the temperature will cause the equilibrium to shift towards the reactants, leading to a decrease in the amount of \(\mathrm{HF}\).

Step-by-step solution

1. Understand Le Chatelier's principle

Le Chatelier's principle helps us to predict the behavior of a chemical equilibrium system when it is disturbed by changes in temperature, pressure, volume, or concentration. In the case of temperature, if the reaction is exothermic (releases heat), increasing the temperature will shift the equilibrium towards the reactants, while decreasing the temperature will shift the equilibrium towards the products. On the other hand, if the reaction is endothermic (absorbs heat), increasing the temperature will shift the equilibrium towards the products, while decreasing the temperature will shift the equilibrium towards the reactants.

2. Identify the type of reaction

We are given the reaction: \(\mathrm{H}_{2}(\mathrm{g})+\mathrm{F}_{2}(\mathrm{g}) \rightleftharpoons 2\mathrm{HF} \Delta H=-538 \mathrm{kJ}(\mathrm{g})\). The negative value of the enthalpy change, \(\Delta H = -538 \mathrm{ kJ}\), indicates that the reaction is exothermic, meaning that it releases heat when it proceeds towards the products.

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

Since the reaction is exothermic, increasing the temperature of the system will cause the equilibrium to shift towards the reactants in order to counteract the imposed change (absorb the additional heat). This means that when the temperature is raised, the amount of product (\(\mathrm{HF}\)) will decrease, and the reaction will move towards the left side of the equation: \(\mathrm{H}_{2}(\mathrm{g})+\mathrm{F}_{2}(\mathrm{g})\).

4. Conclusion

Raising the temperature in the given chemical equilibrium system will not cause the amount of product (\(\mathrm{HF}\)) to increase. Instead, it will cause the equilibrium to shift towards the reactants, leading to a decrease in the amount of \(\mathrm{HF}\).

Key concepts

Chemical Equilibrium

Understanding chemical equilibrium is fundamental to grasping how reactions behave over time. At equilibrium, a chemical system has reached a state where the rate of the forward reaction equals the rate of the reverse reaction. This does not mean the reactants and products are in equal quantities, but rather that their concentrations remain constant over time.

For the reaction between hydrogen and fluorine forming hydrogen fluoride (). In a closed system, when these gases react to form HF, they do so until a balance is reached where HF breaks down into hydrogen and fluorine at the same rate it is formed.). Adjusting conditions such as temperature or pressure can 'tip' this balance, leading to changes in the concentrations of reactants and products according to Le Chatelier's principle.

Exothermic Reaction

An exothermic reaction is one that releases heat, making the surroundings warmer. This release of energy is quantified by the enthalpy change (), which is negative for exothermic reactions. In these reactions, the energy needed to break bonds in the reactants is less than the energy released when new bonds form in the products.

For the reaction under discussion, the formation of HF from hydrogen and fluorine is exothermic, with an enthalpy change of ). This means that as HF is formed, 538 kJ of energy are released for every mole of HF produced. This energy release is a key aspect influencing how the reaction responds to changes in temperature.

Enthalpy Change

Enthalpy change () represents the heat absorbed or released during a reaction at constant pressure. It's an intrinsic characteristic of a chemical reaction. For reactions occurring in gases, as with hydrogen and fluorine reacting to form HF, the enthalpy change provides insights into the nature of the reaction.

A negative value of ) signifies an exothermic reaction. In the given reaction, where ), it indicates that the system releases 538 kJ of energy as heat. Understanding this energy change is crucial because it helps predict how the equilibrium position will shift when external conditions, such as temperature, are altered.