Question

Adult hemoglobin (iron-containing protein) can carry up to four oxygen molecules per hemoglobin molecule, with the addition of oxygen proceeding in a step-wise fashion. For the third step, the value of the equilibrium constant is Keq=5.86 x 10^-4 although the reaction has a (delta Hº) value of -2.9 kj/mol (Remember that the system is not at room temperature).

Heme-Fe^2+ -(O2)2 + O2 <----> Heme-Fe^2+ -(O2)3

Keq=5.86 x 10^-4

(a) calculate delta Gº for this process.

(b)From the information provided, calculate the value of delta Sº for this process.

(c) Compare the value of delta Sº and delta Hº for this process and determine if the oxygenation of hemoglobin at this step is enthaly-driven or entropy-driven when this reaction is spontaneous. Explain your reasoning in a sentence or two.

Answer 1

S = -596.8 J mol^-1oC^-1

c) for this reaction entropy is decreasing that is S is negative and hence, -TS is positive. To make the reacton spontaneous, H should be negative such that the magnitude of H > TS, so that G becomes negative.

Hence, this reacton is enthalpy driven.