In a chemical equation, what do coefficients specify?

• A. The state of matter of each substance
• B. The number of molecules involved
• C. The ratio of reactants to products
• D. The total energy change

Answer: (B)

Coefficients show how many molecules (or moles) of each substance participate in the reaction. They are the numbers in front of the formulas that balance the equation, so they tell you the exact amounts needed for the reaction to proceed while preserving mass. Because of that, reading the coefficients gives the relative quantities of reactants and products—the ratio of how much of each substance is involved. The state of matter (solid, liquid, gas, aqueous) is not determined by these numbers; it’s indicated separately after the substance. The total energy change isn’t set by the coefficients either; energy changes depend on the specific substances and conditions, described by thermodynamic data rather than the counts of molecules.