The free-energy change (?G) for a simple reaction, A ? B, is 0 kJ/mole at 37°C when the concentrations of A and B are 10 M and 0.1 M, respectively. What is the free-energy change for the reaction when the concentrations of A and B are instead 0.01 M and 1 M, respectively? Recall that ?G° = -5.9 × log(K?q). Write down your answer as a number with the appropriate sign (+ or -) and in kJ/mole, e.g. +11.8 kJ/mole.

Question

Quizplus · Accepted Answer

The free-energy change can be written as:
?G = ?G° + RT ln([B]/[A])
When ?G is equal to zero, the system is at chemical equilibrium, and
?G° = - RT ln([B]?q/[A]?q) = - RT ln(10-²) = -5.9 × log (10-²) = +11.8 kJ/mole
When the concentrations are changed, we have:
?G = ?G° + RT ln([B]/[A]) = ?G° + RT ln(10²) = ?G° - RT ln(10-²) = 2 ?G° = +23.6 kJ/mole

The Free-Energy Change (?G) for a Simple Reaction, a