A reacts by two independent

CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry

Problem

A reacts by two independent, one-step pathways to form distinct products

C

and

D

under identical conditions: Pathway 1:

A \xrightarrow[\;E_{a,1}=40\,\text{kJ\,mol}^{-1}\;]{ } C \quad (\Delta G^{\circ}_{1}= -5\,\text{kJ\,mol}^{-1})

Pathway 2:

A \xrightarrow[\;E_{a,2}=120\,\text{kJ\,mol}^{-1}\;]{ } D \quad (\Delta G^{\circ}_{2}= -25\,\text{kJ\,mol}^{-1})

Assume both steps are elementary and first order in

A

. No interconversion occurs between

C

and

D

. (a) Immediately after mixing, which product is expected to form faster? Justify quantitatively or qualitatively with reference to the given activation energies. (b) At long times, which product will be present in the greater molar amount at

298\,\text{K}

? Explain how the standard free-energy data support your prediction. (c) Sketch qualitatively (no numerical scales required) the concentration of

C

and

D

versus time on the same axes, indicating any crossover point and labeling regions of kinetic versus thermodynamic control. (d) Predict how increasing the temperature by

50\,\text{K}

would affect the relative amounts of

C

and

D

(i) after a short time interval and (ii) after a very long time interval. Provide a brief thermodynamic and kinetic rationale for each prediction.

Related theory

Browse the problem library