A manufacturer considers two separate modifications to speed up a gas-phase reaction…
CHEMISTRY · Single correct · A Level · Chemistry · Kinetics · Kinetics
Problem
A manufacturer considers two separate modifications to speed up a gas-phase reaction whose uncatalyzed activation energy is 150kJ mol−1 at 500K. • Modification I: raise the temperature from 500K to 540K. • Modification II: keep the temperature at 500K but lower the activation energy to 130kJ mol−1.
Which statement correctly compares how each modification affects the fraction of molecules able to react?
(a) Modification I produces the larger fractional increase because increasing temperature raises the kinetic energy of every molecule, whereas a catalyst only helps molecules at the transition state.
(b) Both modifications have nearly identical effects because a 40K temperature rise and a 20kJ mol−1 drop in Ea each change the exponential term by about the same amount.
(c) Modification II produces the larger fractional increase because shifting the threshold left captures more of the high-energy tail.
(d) Both modifications will approximately double the reactive fraction since rates typically double with either a small temperature rise or the addition of a catalyst.