Question

the temperature of the reaction is being held at 20^oC. Knowing that at equilibrium the concentration of citrate is 50 mM, oxaloacetate is 0.002 mM, and acetyl-CoA is 0.002mM – what is the net Gibbs Free Energy of the reaction in the test tube? (R=8.314J mol^-1K^-1)? Also, is the reaction spontaneous or non-spontaneous?

Answer 1

Solution:

The conversion of citrate to oxaloacetate and acetyl CO-A is given as,

Citrate = Oxaloacetate + Acetyl Co-A

Thus,

K = [ Oxaloacetate] [acetyl Co-A] / [ Citrate]

K = 0.002 mM x 0.002 mM / 50 mM = 8.0 x 10^-8

G⁰ is related with K as,

G⁰ = - 2.303 RT log K

where, R = gas constant = 8.314 J/mol K-1

T = temperature =20 C = 273 + 20 = 293 K

Hence,

G⁰ = - 2.303 x  8.314 J /mol K x 293 K x log 8.0 x 10^-8

= - 4.49 x 10-4 J/mol

Since, free energy change is negative, hence process is spontaneous.