Which of the following is NOT one of the three factors that affect the rate of a chemical reaction?

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Activation energy is the energy barrier that must be overcome for a reaction to proceed. It’s a property of the reaction pathway, not a direct lever you can turn to change the rate in the same way as temperature, reactant concentration, or a catalyst. Increasing temperature raises the kinetic energy of molecules so more collisions have enough energy to get over that barrier, increasing the rate. Increasing reactant concentration increases the number of collisions per unit time, also speeding up the reaction. A catalyst provides an alternative pathway with a lower activation energy, which increases the rate as well. Because activation energy is a barrier rather than a directly adjustable condition, it’s not one of the three factors that directly affect the rate.