Final answer:
The reaction XA + Y → XY + A can potentially be driven forward by coupling it with ATP hydrolysis under standard conditions and would certainly proceed in a living cell where the actual free energy change for ATP hydrolysis can be higher, making the overall energy change for the coupled reactions negative and spontaneous.
Step-by-step explanation:
If the reaction XA + Y → XY + A has a ΔG°′ of +7.3 kcal/mol, we can consider whether this reaction could be driven by coupling it to the hydrolysis of ATP in a biological system. Under standard conditions, the hydrolysis of ATP to ADP and Pi has a ΔG of -7.3 kcal/mol. This is an exergonic reaction which releases free energy. The reaction under question is endergonic with a ΔG°′ of +7.3 kcal/mol, meaning it requires that same amount of energy to proceed.
Cells use a process called energy coupling to make such endergonic reactions happen by pairing them with exergonic reactions like ATP hydrolysis. To see if ATP hydrolysis can drive the given reaction, we need to calculate the combined ΔG°′ of the coupled reactions. Since the magnitude of the free energy change of ATP hydrolysis is equal to that of the endergonic reaction, when we sum the ΔG°′ values, the overall ΔG°′ for the coupled system becomes zero (-7.3 kcal/mol + 7.3 kcal/mol = 0 kcal/mol). Therefore, the reaction is just at equilibrium under standard conditions, suggesting it could potentially be driven forward by the hydrolysis of ATP under these conditions. However, inside living cells where the actual free energy change for ATP hydrolysis can be as high as -14 kcal/mol, coupling the given reaction with ATP hydrolysis would certainly make it proceed, since the overall energy change would then be negative, allowing the reaction to move forward spontaneously.