Question

How would simultaneously increasing the temperature and volume of the system affect these equilibria? $$ \begin{array}{l}{\text { a. } 2 \mathrm{O}_{3}(\mathrm{g}) \rightleftharpoons 3 \mathrm{O}_{2}(\mathrm{g})+\text { heat }} \\ {\text { b. heat }+\mathrm{N}_{2}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightleftharpoons 2 \mathrm{NO}(\mathrm{g})}\end{array} $$

Short answer

For the first equilibrium, the combined effect of increased temperature and volume cannot be predicted because they counterbalance each other – increasing the temperature shifts the reaction to the left, while increasing the volume shifts the reaction to the right. For the second equilibrium, simultaneously increasing both temperature and volume will shift the equilibrium towards the formation of \(NO(g)\) as both increasing the temperature and volume cause the reaction to shift to the right.

Step-by-step solution

Answering this question for the first equilibrium: \(2 O_3(g) \rightleftharpoons 3 O_2(g) + \textrm{heat}\) We can see that this reaction is exothermic (produces heat) since heat is a product. We will use Le Chatelier's principle to predict the direction of the reaction when the temperature and volume are increased. #Step 2: Determine the effect of increasing the temperature for the first equilibrium#

According to Le Chatelier's principle, when the temperature is increased in an exothermic reaction, the reaction will shift to the left (towards the reactants) in order to decrease the temperature. This means the system will consume heat to counteract the external temperature increase, moving the equilibrium position to the left. #Step 3: Determine the effect of increasing the volume for the first equilibrium#

When the volume is increased, the pressure decreases. According to Le Chatelier's principle, a decrease in pressure will cause the reaction to shift to the side with a greater number of moles of gas in order to restore equilibrium. In this case, there are 2 moles of \(O_3(g)\) on the left side and 3 moles of \(O_2(g)\) on the right side. Therefore, the equilibrium will shift to the right (towards the products). #Step 4: Combine the temperature and volume effects for the first equilibrium#

Increasing the temperature causes the reaction to shift to the left, while increasing the volume causes the reaction to shift to the right. These two effects are opposite and can counterbalance each other. Therefore, the combined effect of increased temperature and volume on the first equilibrium cannot be predicted. #Step 5: Identify the direction of the reaction for the second equilibrium#

Answering this question for the second equilibrium: \( \textrm{heat }+ N_2(g) + O_2(g) \rightleftharpoons 2 NO(g)\) This reaction is endothermic (absorbs heat) since heat is a reactant. #Step 6: Determine the effect of increasing the temperature for the second equilibrium#

According to Le Chatelier's principle, when the temperature is increased in an endothermic reaction, the reaction will shift to the right (towards the products) in order to absorb the additional heat and decrease the temperature. #Step 7: Determine the effect of increasing the volume for the second equilibrium#

As with the first equilibrium, when the volume increases, the pressure decreases. The reaction will shift towards the side with a greater number of moles of gas in response. In this case, there is 1 mole of \(N_2(g)\) and 1 mole of \(O_2(g)\) on the left, compared to 2 moles of \(NO(g)\) on the right. So, the equilibrium will shift to the right (towards the products) to restore equilibrium. #Step 8: Combine the temperature and volume effects for the second equilibrium#

For the second equilibrium, both increasing the temperature and increasing the volume cause the reaction to shift to the right (towards the products). This means that simultaneously increasing both temperature and volume will cause the second equilibrium to shift towards the formation of NO(g).

Key concepts

Chemical Equilibrium

Chemical equilibrium is a state in a chemical reaction where the rate of the forward reaction equals the rate of the reverse reaction. This balance means that the concentrations of reactants and products remain constant over time, although both reactions are still occurring. In a closed system, equilibrium is dynamic, which implies that individual molecules continue to react, but their overall concentrations do not change significantly.

Understanding chemical equilibrium is crucial for predicting how a reaction will respond to various changes, such as alterations in temperature, pressure, or concentration. Le Chatelier's principle offers a valuable tool to forecast the behavior of a reaction at equilibrium when it's subjected to external stresses.

Exothermic Reactions

Heat Release in Exothermic Reactions

Exothermic reactions are processes which release energy, usually in the form of heat. In a chemical equation, heat is often shown as a product. These reactions can include combustion, many oxidation reactions, and neutralizations, where energy is given off to the surroundings, causing the temperature to rise.

When external conditions, such as temperature, are changed, exothermic reactions respond in a way that can be predicted by Le Chatelier's principle. If the temperature is increased, the system will try to counteract this by shifting the equilibrium position towards the reactants, absorbing the added heat and slightly cooling the system. Conversely, decreasing the temperature can shift the reaction towards producing more heat, hence favoring the products.

Endothermic Reactions

Absorption of Energy in Endothermic Reactions

Endothermic reactions are the opposite of exothermic reactions. They require an input of energy, usually in the form of heat, from the surroundings to proceed. In chemical equations, heat is typically denoted as a reactant. Endothermic processes consist of photosynthesis, evaporation, and melting ice cubes.

Applying Le Chatelier's principle to endothermic reactions tells us that raising the temperature will push the equilibrium toward the products, as the system uses more heat from the surroundings to progress the reaction. If the temperature is decreased, the reaction is shifted toward the reactants, as the system releases energy to the surroundings to maintain its equilibrium.

Equilibrium Shift

Predicting the Direction of a Shift

The concept of an equilibrium shift is essential when predicting how a system will respond to changes such as pressure, volume, or temperature. According to Le Chatelier's principle, if a system at equilibrium is disturbed, it will respond to minimize the disturbance and re-establish equilibrium. This can manifest as changes in concentrations of reactants and products, depending on the nature of the disturbance.

For example, increasing the volume of a system will decrease the pressure, causing the equilibrium to shift toward the side with more moles of gas, increasing pressure to compensate. Increasing temperature in an exothermic reaction shifts the equilibrium toward the reactants, while it shifts to products in an endothermic reaction. These rules allow us to predict the response of a system to maintain equilibrium under various conditions.