What is the term for the number in front of a chemical formula in an equation that indicates how many molecules or atoms of each reactant and product are involved in a reaction?

The term you are looking for is “coefficient.” In a chemical equation, coefficients are the numbers placed in front of the chemical formulas. They indicate the quantity of each substance involved in the reaction.

For example, in the equation:

2 H₂ + O₂ → 2 H₂O

The coefficient “2” in front of H₂ and H₂O means that there are two molecules of hydrogen gas and two molecules of water produced. Coefficients are crucial for balancing chemical equations, as they ensure that the law of conservation of mass is upheld; that is, the number of atoms of each element is the same on both sides of the equation.