Which of the following methods will increase the speed of molecules, thereby increasing the rate of a chemical reaction?

• A. Decrease the concentration of reactants
• B. Lower the pressure for a reaction involving gases
• C. Add an inert gas at constant volume
• D. Increase the temperature of the reaction mixture

Answer: (D)

Verified step by step guidance

1. Understand that the speed of molecules in a reaction is directly related to their kinetic energy, which depends on temperature. Increasing temperature increases molecular speed.
2. Recognize that decreasing the concentration of reactants reduces the number of collisions per unit time, which generally decreases the reaction rate, not increases molecular speed.
3. Lowering the pressure in a reaction involving gases decreases the number of gas molecules per volume, reducing collision frequency but does not increase molecular speed.
4. Adding an inert gas at constant volume increases total pressure but does not affect the partial pressures of reactants or their molecular speeds, so it does not increase reaction rate.
5. Conclude that increasing the temperature is the only method listed that increases molecular speed and thus increases the rate of a chemical reaction.