Question

Blue-green algae (otherwise known as cyanobacteria), found in the surface waters of Lake, “fix” N₂(g) to make NH₄⁺as their source of nitrogen, coupled with the consumption of glucose to form CO₂(g). In this lake, at equilibrium with the atmosphere, pH = 8, [NH₄⁺] = 10-5 M, and [C₆H₁₂O₆] = 10^-5 M. How much energy is needed for or gained from nitrogen fixation?

Answer 1

the nitrogen fixation from to reaction is

From standard reduction potential table E=-0.28V

The reaction of glucose consumption is

In lake M

M

M

From Nernst equation

From first reaction

For 1 mole electrons required = 3 e

for M electrons required =

energy is needed for nitrogen fixation.

That energy will be produced by glucose digestion into CO2.