Two gas-phase reactions occur at the same temperature
CHEMISTRY · Single correct · A Level · Chemistry · Kinetics · Kinetics
Problem
Two gas-phase reactions occur at the same temperature.
I. F+Cl2→ClF+Cl
II. F+CF3Cl→CF3F+Cl
Reaction II proceeds much more slowly than reaction I even though experimental data show that both reactions have similar activation energies. Which of the following best explains the difference in reaction rates?
(a) The greater molar mass of CF3Cl lowers its average molecular speed, resulting in fewer total collisions in reaction II.
(b) Electron affinity of F toward chlorine is higher than toward carbon, so F reacts preferentially with Cl2 in reaction I.
(c) The bulky CF3 group in reaction II decreases the probability that an F atom will collide with the C–Cl bond in the correct orientation.
(d) Breaking the C–Cl bond in CF3Cl requires more energy than breaking the Cl–Cl bond in Cl2, so reaction II has a larger activation energy and proceeds more slowly.