Question

Suppose the reaction system $$\mathrm{UO}_{2}(s)+4 \mathrm{HF}(g) \rightleftharpoons \mathrm{UF}_{4}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)$$ has already reached equilibrium. Predict the effect of each of the following changes on the position of the equilibrium. Tell whether the equilibrium will shift to the right, will shift to the left, or will not be affected. a. Additional \(\mathrm{UO}_{2}(s)\) is added to the system. b. 5.0 mol of \(\mathrm{Xe}(g)\) is added to the system. c. The reaction is performed in a glass reaction vessel; HF(g) attacks and reacts with glass. d. Water vapor is removed. e. The size of the reaction vessel is increased.

Short answer

a. No effect on the equilibrium position. b. No effect on the equilibrium position. c. The equilibrium position shifts to the left. d. The equilibrium position shifts to the right. e. The equilibrium position shifts to the left.

Step-by-step solution

a. Adding more \(\mathrm{UO}_{2}(s)\) to the system:

UO2 is a solid, so adding more will not affect the concentration of the components in the gas phase. Thus, the position of the equilibrium will not be affected.

b. Adding 5.0 mol of \(\mathrm{Xe}(g)\) to the system:

Xe is an inert gas and does not participate in the reaction. Adding an inert gas will increase the total pressure, but it will not change the partial pressures of the reacting gases. Therefore, the equilibrium position will not be affected.

c. HF(g) reacts with the glass reaction vessel:

As HF(g) reacts with the glass, it is effectively being removed from the system. This will cause the concentration of HF(g) to decrease. According to Le Chatelier's Principle, the system will respond by shifting the equilibrium to the side with more HF(g) to counteract the decrease in concentration. In this case, the equilibrium will shift to the left.

d. Water vapor is removed:

When water vapor is removed, the concentration of \(\mathrm{H}_{2}\mathrm{O}(g)\) decreases. According to Le Chatelier's Principle, the system will respond by shifting the equilibrium towards the side with more H2O(g) to counteract the decrease in concentration. In this case, the equilibrium will shift to the right.

e. Increasing the size of the reaction vessel:

Increasing the size of the reaction vessel will cause the total pressure to decrease. According to Le Chatelier's Principle, the system will respond by shifting the equilibrium position to the side with more gas particles (higher molar volume) to counteract the decrease in pressure. In this case, we can see that there are 4 moles of gas on the reactant side (4 moles of HF(g)) and 3 moles of gas on the product side (1 mole of \(\mathrm{UF}_{4}(g)\) and 2 moles of H2O(g)). The equilibrium will shift to the left, where there are more gas particles.

Key concepts

Le Chatelier's Principle

Le Chatelier's Principle is a fundamental concept used to predict how a chemical system at equilibrium reacts to changes in its conditions. In essence, the principle states that if an external change is imposed on a system at equilibrium, the system will adjust itself to partially counteract the change and establish a new equilibrium state.

Imagine a seesaw balanced in the middle—this represents a chemical reaction at equilibrium. If you were to add weight to one side, the seesaw would no longer be level. According to Le Chatelier's Principle, the system will try to restore balance. In the context of a chemical reaction, this could mean shifting the equilibrium position to either produce more products or more reactants, depending on the nature of the external change. This principle helps us understand how changes in concentration, pressure, and temperature affect the equilibrium position in a chemical reaction.

Reaction Equilibrium Shift

When a system in equilibrium is disturbed, the position of equilibrium can shift either to the right, favoring the formation of products, or to the left, favoring the formation of reactants. The direction depends on the change made to the system.

For example, if a reactant is added to the system, the equilibrium might shift to the right to produce more products, attempting to counterbalance the increase in reactant concentration. Conversely, if a product is removed from the system, this could also cause a shift to the right as the system tries to produce more product to compensate for its loss. The concept of an equilibrium shift is a direct application of Le Chatelier's Principle and is critical in understanding how chemical reactions adapt to changes in the environment.

Effect of Concentration Change

Concentration changes can have a significant effect on the position of an equilibrium system. According to Le Chatelier's Principle, if the concentration of a reactant or product is changed, the system will respond by shifting the equilibrium to counteract the alteration.

Increasing the concentration of a reactant generally causes the equilibrium to shift to the right, promoting the formation of more products. Conversely, decreasing the concentration of a reactant often results in a shift to the left, forming more reactants. Similarly, an increase in the concentration of a product would usually shift the equilibrium to the left (towards reactants), while a decrease in product concentration would shift it to the right (towards more products). This reaction to concentration change is essential for chemists when they want to increase the yield of a desired product in chemical reactions.

Effect of Pressure Change

Pressure changes can also impact systems at equilibrium that involve gases. When the pressure of an equilibrium system is altered, Le Chatelier's Principle predicts that the system will adjust itself to counteract the change in pressure.

If the pressure is increased by decreasing the volume of the system, the equilibrium will typically shift towards the side with fewer gas molecules. This is because having fewer gas molecules would result in a smaller total volume, effectively counteracting the pressure increase. Conversely, if the pressure is decreased by increasing the volume of the system, the equilibrium will shift towards the side with more gas molecules, increasing the number of collisions and partially restoring the lost pressure. It is essential to note that pressure changes do not affect solid or liquid compounds in the reaction, as their volumes are not significantly impacted by pressure variations.