Adding powdered limestone (calcium carbonate) to a lake affected by acid rain can decrease the availability of phosphate ion, an important nutrient, but not nitrate ion another nutrient. Write a balanced equation and calculate the standard free energy change for the process to confirm its spontaneity.

The reaction is:

H⁺

CaCO₃ ⇄ Ca²⁺ + CO₃ ⇄ HCO₃

The standard free energy change is ΔG = ΔH - TΔS

Explanation:

Limestone is a mineral familiar with calcium carbonate, and being very common, the acid present in acid rain dissolves it reacting with carbonate, since the acids present in acid rain are characterized by being highly soluble in water and are also strong acids. The reaction is as follows:

H⁺

CaCO₃ ⇄ Ca²⁺ + CO₃ ⇄ HCO₃

The spontaneity of the reaction is equal to:

ΔG = ΔH - TΔS

The sign of the standard free energy changes from positive to negative.