What is the coefficient in a chemical equation?

In a chemical equation, the coefficient is a number that appears in front of a chemical formula to indicate the relative number of moles of each substance involved in the reaction. Coefficients are used to balance chemical equations, ensuring that the same number of atoms of each element is present on both the reactant and product sides of the equation.

For example, in the balanced chemical equation for the combustion of methane (CH4) with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O):

CH4 + 2O2 → CO2 + 2H2O

The coefficients are as follows:

1 in front of CH4 means there is 1 mole of methane.
2 in front of O2 means there are 2 moles of oxygen molecules.
1 in front of CO2 means there is 1 mole of carbon dioxide.
2 in front of H2O means there are 2 moles of water molecules.
Balancing the coefficients ensures that the same number of carbon, hydrogen, and oxygen atoms are present on both sides of the equation, obeying the law of conservation of mass.