Table of contents

This is an oxidation-reduction (redox) reaction:

2 P0 + 6 e- → 2 P-III (reduction)

3 Mg0 - 6 e- → 3 MgII (oxidation)

P is an oxidizing agent, Mg is a reducing agent.

Word equation

magnesium + red phosphorus → magnesium phosphide

Input interpretation

3Mg + P2 → Mg3P2

Magnesium red phosphorus magnesium phosphide


Balanced equation

Balance the chemical equation algebraically:

3Mg + P2 → Mg3P2

Add stoichiometric coefficients, c1, to the reactants and products:

c13Mg + c2P2 → c3Mg3P2

Set the number of atoms in the reactants equal to the number of atoms in the products for Mg and P:

Mg: c1 = 3c3

P: c2 = 2c3

Since the coefficients are relative quantities and underdetermined, choose a coefficient to set arbitrarily. To keep the coefficients small, the arbitrary value is ordinarily one. For instance, set c3 = 1 and solve the system of equations for the remaining coefficients:

 c1 = 3 c2=2


Substitute the coefficients into the chemical reaction to obtain the balanced



3Mg + P2 → Mg3P2