Some bacteria get their energy from reduction of CO2 to CH4 by H2.

1. How many electrons are required to reduce CO2 to CH4?
2. Calculate the G for formation of methane based on the two standard reduction potential of -0.171V for reduction of CO2 to CH4 and -0.414V for reduction of H+ to H2.

4H2 + CO2 ==> CH4 + 2H2O

You have 2H2 ==> 4H^+ + 4e
and 2H2 + 4e ==> 4H^-
so (a) is 4 electrons.
If you add -.171 + 0.414 = ?
Then dG = -nEF to calculate dG.

To determine the number of electrons required to reduce CO2 to CH4, we can look at the balanced chemical equation for the reaction:

CO2 + 8H+ + 8e- → CH4 + 2H2O

From the equation, we can see that 8 electrons are required to reduce one molecule of CO2 to one molecule of CH4.

Now, let's calculate the standard Gibbs free energy change (ΔG) for the formation of methane based on the two standard reduction potentials given:

ΔG = -nFΔE

Where:
- ΔG is the standard Gibbs free energy change,
- n is the number of electrons transferred in the reaction,
- F is the Faraday constant (approximately 96485 C/mol), and
- ΔE is the difference between the reduction potentials.

Given:
- ΔE1 = -0.171V (reduction of CO2 to CH4)
- ΔE2 = -0.414V (reduction of H+ to H2)

Let's calculate ΔG:

ΔG = -8 * 96485 C/mol * (ΔE1 - ΔE2)

Substituting the given values:

ΔG = -8 * 96485 C/mol * (-0.171V - (-0.414V))

Now, calculate the value and you will have the standard Gibbs free energy change (ΔG) for the formation of methane.