Stoichiometric coefficients are numbers used in chemical equations to indicate the relative amounts of reactants and products involved in a reaction. They show how many molecules or moles of each substance participate in the reaction, helping to balance the equation according to the law of conservation of mass. For example, in the equation 2H2 + O2 → 2H2O, the coefficients 2 and 1 indicate that two molecules of hydrogen react with one molecule of oxygen to produce two molecules of water. These coefficients are essential for calculations in stoichiometry, which is the study of the quantitative relationships in chemical reactions. By using stoichiometric coefficients, chemists can determine how much of each reactant is needed or how much product will be formed. This understanding is crucial for various applications, including pharmaceuticals, industrial processes, and environmental science.