CHEMISTRY · Single correct · A Level · Chemistry · Kinetics · Kinetics
Problem
A reaction is carried out at both 300 K and 600 K. Adding a catalyst lowers the activation energy by 30 kJ mol−1. The catalyzed rate is found to be roughly 500 times faster than the uncatalyzed rate at 300 K but only about 20 times faster at 600 K. Which statement most plausibly accounts for the larger relative rate increase at the lower temperature?
(a) Heat released during the reaction deactivates the catalyst more rapidly at 600K, reducing its effectiveness compared with 300K.
(b) The concentration of catalyst is higher at 300K than at 600K, so its influence on rate is greater at the lower temperature.
(c) At lower temperature, far fewer molecules have sufficient energy to overcome the original activation barrier, so reducing that barrier has a proportionally larger effect.
(d) At high temperature adsorption of reactants onto the catalyst surface is inefficient, so the catalyst can only accelerate the reaction significantly at 300K.