In ordinary chemical reactions, if there is no reactant left in excess, what is the described relation between the products and the reactants?

• A. The amount of product formed equals the sum of the reactants
• B. The amount of product formed is greater than the reactants
• C. All reactants remain unreacted
• D. There is no reaction

Answer: (A)

When a reaction goes to completion because there is no reactant left in excess, everything that could react has reacted and turned into products. The amount of product you get is determined by how much reactant was available and the way those reactants combine, i.e., the stoichiometry. In a simple case where the reaction consumes reactants in a 1:1 ratio to form one unit of product, the total amount of product formed equals the total amount of reactants that participated. If both reactants are used up completely, the product yield reflects the combination of those reactants that were present. So, under these conditions, the product quantity is tied directly to the reactants that reacted, which is why the statement describes the product amount as matching the reactants’ contribution. In more complex cases with different coefficients, you still use the balanced ratios to relate amounts, but the essential idea remains: no excess reactant means all usable reactants are converted to product.