The table shows the time required for a substitution reaction to consume 90 % of the…
CHEMISTRY · Single correct · A Level · Chemistry · Kinetics · Kinetics
Problem
The table shows the time required for a substitution reaction to consume 90 % of the limiting reactant under three different conditions.
Trial
Additive(s) present
Time to 90 % completion (s)
1
none
200
2
0.010 g Ni
20
3
0.010 g Ni + 0.001 g P
180
Which statement is most consistent with the data?
(a) Phosphorus reacts with the limiting reactant to form a less-reactive intermediate, so the presence of both additives in Trial 3 slows the reaction toward the uncatalysed rate.
(b) Phosphorus acts as a catalyst poison by occupying active sites on the nickel surface, thereby diminishing the catalytic effect observed in Trial 2.
(c) Nickel initially adsorbs reactant molecules so strongly that it slows the reaction, while phosphorus frees some of these molecules, explaining the intermediate rate observed in Trial 3.
(d) Nickel and phosphorus form a surface alloy that blocks most active sites at first; only after a slow restructuring does it become catalytic, so the overall reaction in Trial 3 appears slower than with nickel alone.