Why can’t we just harvest the oxygen in H20 and breathe under water

Question

Why can’t we just harvest the oxygen in H20 and breathe under water

In: Chemistry

Answer 1

“The electrolysis of water in standard conditions requires a theoretical minimum of 237 kJ of electrical energy input to dissociate each mole of water, which is the standard Gibbs free energy of formation of water. It also requires thermal energy to balance the change in entropy of the reaction.”

So, 237kJ minimum to get 32g of oxygen.

Apparently, humans use about 750g per day, so:

750g ÷ 32g × 237kJ = 5555kJ … which is about 1300 kcal. Presumably we use less getting it from the air.