What is  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?

coefficient There are 3 major parts for each reactant in a formula. That would be the coefficient, subscript, and element. For instance, the burning of methane (CH4) in oxygen. The unbalanced formula is CH4 + O2 => CO2 + H2O The numbers 2 and 4 above should all be subscripts, but I'm limited in my ability to type them. And the letters each represent elements. If you carefully count the number of atoms for each element, you'll soon determine that they don't match. For instance, the left side has 1 carbon, 4 hydrogen, and 2 oxygen. Bu the right side has 1 carbon, 2 hydrogen and 3 oxygen. To balance the equation, we need to add coefficients to the equation so that the number of atoms for each element matches. The balanced formula, created by adding coefficients is CH4 + 2 O2 => CO2 + 2 H2O Which now has 1 carbon, 4 hydrogen, and 4 oxygen on both sides.