CHEMISTRY · Single correct · A Level · Chemistry · Kinetics · Kinetics
Problem
At temperatures above 500 °C, the rate of an industrial gas-phase reaction no longer increases significantly with further heating. Which statement most plausibly accounts for this observation?
(a) Virtually all molecules already possess enough energy to overcome the activation barrier, so further heating cannot increase the reaction rate.
(b) Side reactions or thermal decomposition of reactants begin to compete, effectively limiting the net rate of the desired reaction.
(c) The collision frequency of the gas molecules cannot increase any further once they are moving so rapidly, so the rate plateaus.
(d) The catalyst surface becomes saturated with reactant molecules, so additional heating has little effect on the overall rate.