Question

For an exothermic chemical process occurring in two steps as (i) A+B→X (Slow) and (ii) X→AB (Fast). The progress of the reaction can be best described by:

• A.

  

• B.

  

• C.

  

Answer 1

The correct option is B

An explanation for correct option:

Option (B);

• Given that, the reaction is an exothermic process occurring in two steps as (i)$\mathrm{A}+\mathrm{B}\to \mathrm{X}$(Slow) and (ii) $\mathrm{X}\to \mathrm{AB}$ (Fast).
• For the slower step (i) the activation energy curve will be higher, hence the energy peak will be higher.
• For the faster step(ii) the activation energy curve will be lower, hence the energy peak will be lower.

An explanation for incorrect option:

Option (A);

• The given reaction is a two-step reaction, having two peaks.
• In the given option, only one peak is given, hence it doesn't refer to as the given exothermic reaction.

Option (C);

• The given reaction is a two-step reaction, where the first peak as the slower step would show a higher energy peak and the second peak as the faster step would show a lower energy peak.
• In the given option, the first peak has a lower energy peak and the second has a higher energy peak, which doesn't satisfy the given condition.

Hence, the progress of the given reaction can be best described by Option (B).