When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme phosphohexose isomerase, the final mixture contains twice as much glucose 6-phosphate as fructose 6-phosphate. Which one of the following statements is most nearly correct, when applied to the reaction below (R = 8.315 J/mol·K and T = 298 K)?
Glucose 6-phosphate : fructose 6-phosphate
A.) ΔG'° is +1.7 kJ/mol.
B.) ΔG'° is –1.7 kJ/mol.
C.) ΔG'° is incalculably large and negative.
D.) ΔG'° is incalculably large and positive.
E.) ΔG'° is zero.

The correct answer is A:  (ΔG'° is +1.7 kJ/mol).

Explanation:

Step 1: Data given

The final mixture contains twice as much glucose 6-phosphate as fructose 6-phosphate.

R = 8.315 J/mol*K

T = 298 K

Step 2:

Keq = [fructose 6-phosphate]/[glucose 6-phosphate] = 1/2

ΔG'° = -RT ln (Keq)

ΔG'° = -RT ln (1/2)

⇒with R = 8.315 J/mol

⇒with T = the temperature = 298 K

ΔG'° = -8.315 * 298 * ln (1/2)

ΔG'° = -8.315 * 298 * -0*693

ΔG'° = 1717 J/mol

ΔG'° = 1.7 * 10³ J/mol = 1.7 kJ/mol

The correct answer is A:  (ΔG'° is +1.7 kJ/mol).

- lead + phosphoric acid = hydrogen + lead(ii) phosphate