### Correct Option: C. Concentration of SO₃ increases #### Explanation of the Correct Answer: 1. **Understanding the Reaction**: The given reaction is: \[ 2SO_2(g) + O_2(g) \leftrightarrow 2SO_3(g) \] This is an exothermic reaction, meaning it releases heat when the reactants (sulfur dioxide and oxygen) convert into the product (sulfur trioxide). 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, we are reducing the temperature of the reaction. 3. **Effect of Temperature on Exothermic Reactions**: For exothermic reactions, heat can be considered a product. When the temperature is decreased, the system will respond by favoring the formation of products to produce more heat. Therefore, lowering the temperature shifts the equilibrium to the right, towards the formation of more SO₃. 4. **Conclusion**: As a result of lowering the temperature from 800°C to 500°C, the concentration of SO₃ will increase because the equilibrium shifts to the right to produce more SO₃ in order to counteract the decrease in temperature. #### Explanation of Why Other Options are Incorrect: - **Option A: The reaction rate increases** - **Why it's wrong**: Generally, reaction rates increase with temperature due to higher kinetic energy of the molecules, which leads to more frequent and effective collisions. Lowering the temperature (from 800°C to 500°C) would decrease the kinetic energy of the molecules, thus slowing down the reaction rate. Therefore, this option is incorrect. - **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 favors the production of SO₃, so the concentration of SO₃ will actually increase, not decrease. - **Option D: SO₂ gas becomes unreactive** - **Why it's wrong**: This statement is misleading. Lowering the temperature does not make SO₂ unreactive; it simply affects the rate of reaction and the position of equilibrium. SO₂ will still be reactive, but the rate at which it reacts to form SO₃ will decrease due to the lower temperature. ### Summary of Key Points: - The reaction is exothermic, meaning it releases heat. - Lowering the temperature shifts the equilibrium to the right, favoring product formation (SO₃). - According to Le Chatelier's Principle, the system compensates for the temperature decrease by producing more SO₃. - Reaction rates generally decrease with lower temperatures, and SO₂ remains reactive. This thorough understanding of the principles governing chemical equilibria and reaction kinetics is crucial for mastering concepts in chemistry, especially in the context of professional exams.