The distribution of Na+ ions across a typical biological membrane is 10 mmol/L inside the cell and 140 mmol/L outside the cell. At equilibrium the concentrations would be equal, but in a living cell the ions are not at equilibrium.
A) What is the Gibbs free-energy difference for Na+ ions across the membrane at 37°C (normal body temperature)?
The concentration differential must be maintained by coupling to reactions that have at least that difference of Gibbs free energy.