Question

which statement about reaction rates is true?
changing the temperature cannot speed up a reaction rate.
a catalyst slows down the reaction rate.
changing the amount of reactants will not change the reaction rate.
changing the surface area affects the reaction rate.

Explanation:

• Temperature effect: Increasing temperature generally speeds up reaction rates as it provides more kinetic energy to reactant molecules. So, the statement "Changing the temperature cannot speed up a reaction rate" is false.
• Catalyst role: A catalyst speeds up a reaction rate by lowering the activation energy, not slows it down. So, the statement "A catalyst slows down the reaction rate" is false.
• Reactant amount (for non - zero - order reactions): For many reactions (especially non - zero - order reactions), changing the amount of reactants (concentration for solutions, pressure for gases) can change the reaction rate. So, the statement "Changing the amount of reactants will not change the reaction rate" is false.
• Surface area effect: For reactions involving solids, a larger surface area means more reactant particles are available for collision. For example, a powdered solid reacts faster than a large chunk of the same solid. So, "Changing the surface area affects the reaction rate" is true.

Answer:

Changing the surface area affects the reaction rate.