# Finding ΔG and K for a given redox reaction

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1. Apr 5, 2009

### anisotropic

1. The problem statement, all variables and given/known data

Redox reaction:
B-hydroxybutarate + 1/2O2 -> acetoacetate + H2O

Half reaction 1:
O2 + 4H+ + 4e- -> 2H2O (E = +0.816 V)

Half reaction 2:
acetoacetate + 2H+ + 2e- -> B-hydroxybutarate (E = -0.346 V)

Using standard reduction potentials given,

• calculate ΔG
• calculate the equilibrium constant, K

Conditions are the biochemist's standard state, pH 7, 298.15 K.

2. Relevant equations

ΔG = -nFΔE

ln K = nFE/RT

3. The attempt at a solution

ΔErxn = (0.816 V) + (0.346 V)
ΔErxn = 1.162 V

ΔG = -nFΔE
ΔG = -n(96485 C/mol)(1.162 V)

n = ? (moles of electrons transferred)

By writing out both half reactions, the electrons cancel out. Should there not be electrons left over on one side of the equation in order to determine the value of n?

Last edited: Apr 5, 2009
2. Apr 5, 2009

### Staff: Mentor

No, if electrons are left, reaction is not balanced.

3. Apr 7, 2009

### anisotropic

So 2 mol of e- per mol of product (n = 2)?

4. Apr 12, 2009

### anisotropic

Can someone please confirm this?