### Correct Option: C. Concentration of SO3 increases #### Explanation of the Correct Answer: 1. **Understanding the Reaction**: The given reaction is: \[ 2SO_{2(g)} + O_{2(g)} \rightleftharpoons 2SO_{3(g)} \] This is an exothermic reaction, meaning it releases heat when it proceeds in the forward direction (producing \(SO_3\)). 2. **Le Chatelier's Principle**: This principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change. In this case, reducing the temperature is the change we are considering. 3. **Effect of Temperature on Exothermic Reactions**: For exothermic reactions, lowering the temperature favors the formation of products. This is because the system will try to produce more heat to counteract the decrease in temperature. Therefore, when the temperature is reduced from 800ºC to 500ºC, the equilibrium will shift to the right, favoring the production of \(SO_3\). 4. **Conclusion**: As a result of this shift, the concentration of \(SO_3\) will increase as the reaction moves towards producing more products to restore equilibrium. #### Explanation of Why Other Options Are Incorrect: - **Option A: The reaction rate increases** - **Why it's wrong**: Generally, lowering the temperature decreases the kinetic energy of the molecules involved in the reaction. This results in fewer effective collisions between reactant molecules, which typically slows down the reaction rate. Therefore, while the equilibrium shifts to favor products, the rate of the reaction itself does not increase. - **Option B: Concentration of SO3 decreases** - **Why it's wrong**: This option contradicts the application of Le Chatelier's Principle. As explained, lowering the temperature for an exothermic reaction shifts the equilibrium towards the products, leading to an increase in the concentration of \(SO_3\), not a decrease. - **Option D: SO2 gas becomes unreactive** - **Why it's wrong**: This statement is misleading. Lowering the temperature does not make \(SO_2\) unreactive; it simply affects the rate of reaction and the position of equilibrium. \(SO_2\) remains a reactive species, and its ability to participate in the reaction is not eliminated by a temperature change. ### Summary of Key Points: - **Exothermic Reactions**: Lowering temperature favors product formation. - **Le Chatelier's Principle**: A system at equilibrium will shift to counteract changes in conditions. - **Reaction Rate**: Decreases with lower temperature due to reduced kinetic energy. - **Equilibrium Shift**: In this case, the shift favors the production of \(SO_3\), increasing its concentration. This understanding is crucial for predicting the behavior of chemical systems under varying conditions, especially in exothermic reactions.