What is the general effect of increasing pressure on the reaction rate for gas-phase reactions?

• A. Higher pressure generally increases rate due to increased concentration of reacting gas molecules.
• B. Higher pressure generally decreases rate due to compression.
• C. Pressure has no effect on gas-phase reaction rate.
• D. Increasing pressure only affects equilibrium, not rate.

Answer: (A)

Increasing pressure in a gas raises the number of molecules per unit volume, so the concentrations of the reacting gases go up. Since reaction rate depends on how often reacting molecules collide, higher concentration means more collisions per second and faster formation of products. This kinetic effect is why gas-phase reactions generally speed up when pressure increases (assuming temperature is kept constant). The idea that pressure only affects equilibrium or that compression would slow things down doesn’t match how rate depends on collision frequency.