A chemist has the four reactions listed below available in the laboratory at 298 K
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
A chemist has the four reactions listed below available in the laboratory at 298 K. All species are in their standard states.
Equation
ΔG° (kJ mol⁻¹)
(I) A → B
+10
(II) B + C → D
+15
(III) C → E
–25
(IV) E → D
–8
The chemist’s goal is to convert one mole of substance A into product D while ensuring that the overall ΔG° lies between –5 kJ mol⁻¹ and –20 kJ mol⁻¹.
(a) Select a set of one or more of the reactions (I)–(IV) whose sum accomplishes the desired conversion of A into D. Justify quantitatively that your chosen set produces the target product without leaving any net intermediate species.
(b) Show the algebraic summation of the chosen reactions, clearly indicating which intermediates cancel and how stoichiometric coefficients are adjusted, if at all.
(c) Calculate the ΔG° for the overall process you constructed in part (a). Demonstrate that the value falls within the required window, and state whether the overall reaction is spontaneous under standard conditions.
(d) Propose any alternative combination of the listed reactions that also converts A to D. If no alternative exists, explain why. Support your answer with thermodynamic reasoning.