CHEMISTRY · Single correct · A Level · Chemistry · Kinetics · Kinetics
Problem
During an experiment, the initial rate of an ammonia synthesis catalyst increases with nitrogen pressure but eventually levels off, even though pressure continues to rise. Which statement best explains the observed plateau in rate?
(a) The reaction has reached overall equilibrium, so raising the nitrogen pressure cannot push the rate any higher.
(b) Because the hydrogen pressure is unchanged, H2 becomes the limiting reactant at high N2 pressure, preventing any further rate increase.
(c) All available surface sites become occupied by N2, so further increases in nitrogen do not raise the fraction of reactive sites.
(d) Ammonia molecules cover all the surface sites at high pressure, blocking additional nitrogen from adsorbing and stopping the rate increase.