Question

The step that completes the citric acid cycle is the conversion of malate (M) to oxaloacetate (OA) by NAD+. The two redox half cells that are coupled for this reaction are oxaloacetate + 2 H+ + 2 e- double arrow malate, ε°’ = -0.166 V and NAD+ + H+ + 2 e- double arrow NADH, ε°’ = -0.320 V. What is the equilibrium constant Keq’ for the conversion of M to OA by NAD+?

Answer 1

Reactions provided are:

  E= -0.166 V

E = -0.32 V

We are asked the conversion of Malate to OA

We need to put the malate reaction in the opposite way, by doing this we need to change the E value (-0.166) to (+0.166)

E = 0.166 V (This is an oxidation because the reactants lose electrons)

E = -0.32 V

Now we add the equations to get the global equation

Also we get the total E cell by adding the values 0.166 - 0.32 = -0.154 V

Now we can relate the definitions of Gibbs energy in order to calculate the Keq

n is the number of moles that are transferred, in this case there are 2 electrons

F is a constant number "faraday constant" with a value of 96, 500

Solving the equations