Consider the reaction H₂(g) + I₂(g) → 2 HI(g). The reaction of a fixed amount of H₂ and I₂ is studied in a cylinder fitted with a movable piston. Indicate the effect of each of the following changes on the rate of the reaction. (b) An increase in volume at constant temperature

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1. Understand the relationship between volume and pressure: According to Boyle's Law, at constant temperature, an increase in volume results in a decrease in pressure.
2. Consider the effect of pressure on reaction rate: For reactions involving gases, a decrease in pressure (due to increased volume) generally leads to a decrease in the concentration of the gaseous reactants.
3. Relate concentration to reaction rate: According to the rate law, the rate of a reaction is directly proportional to the concentration of the reactants. Therefore, a decrease in concentration typically results in a decrease in the reaction rate.
4. Apply the concept to the given reaction: In the reaction H2(g) + I2(g) → 2 HI(g), increasing the volume at constant temperature decreases the concentration of H2 and I2, thus decreasing the rate of the reaction.
5. Summarize the effect: An increase in volume at constant temperature will decrease the rate of the reaction due to the reduced concentration of the gaseous reactants.