Which of the following is NOT one of the five factors affecting reaction rate?

• A. Concentration
• B. Pressure
• C. Temperature
• D. Catalysts

Answer: (B)

Reaction rate depends on how often reacting particles meet in a way that leads to products, and this is mainly governed by temperature, concentration, surface area, and catalysts. Temperature raises kinetic energy so a larger fraction of collisions have enough energy to overcome the activation barrier. Higher concentration increases the number of collisions per unit time. Greater surface area for solid reactants provides more contact points for collisions. A catalyst offers an alternative pathway with lower activation energy, increasing the fraction of effective collisions. Pressure, however, is not a universal factor because it primarily affects gas-phase reactions by changing the concentration of gaseous molecules; for liquids and solids, changing pressure often has little impact on collision frequency or energy. Since pressure does not influence most reactions in the same broad way as the others, it’s not regarded as one of the general factors affecting reaction rate.