Stoichiometry and Reaction Yield

From coefficients to product amount

Coefficients in a balanced reaction specify mole ratios. Multiply the amount of A by the product coefficient and divide by the coefficient of A to find the theoretical product amount. If the starting amount is a mass, first divide it by the molar mass. Multiply the final product amount by its molar mass to obtain a mass. The initial molar masses are illustrative inputs only.

Limiting reagent and yield

For two reactants compare their n/ν ratios. The smaller ratio sets the maximum reaction extent. For 2A + B → 2P, 4 mol of A and 3 mol of B produce 4 mol of P and leave 1 mol of B. Collecting 15 g when the theoretical mass is 20 g gives a yield of 75 percent. Values above 100 percent may indicate impurities or measurement problems. This calculation does not establish whether a reaction will occur or whether it is safe.

Compare coefficients with mole amounts

In an abstract example, let the balanced reaction be 3A + 2B → 4P. Choose initial amounts of 9 mol A and 4 mol B. The extent allowed by A is 9 / 3 = 3 mol, while that allowed by B is 4 / 2 = 2 mol. The smaller value makes B limiting. Theoretical product is 4 × 2 = 8 mol and remaining A is 9 − 3 × 2 = 3 mol. B is fully consumed. This is an illustration of mole ratios, not a claim that a particular chemical reaction exists.

Do not apply coefficients directly to masses. Convert a mass in grams to moles by dividing by that substance's molar mass first. Multiplying every reaction coefficient by the same factor should leave product amount unchanged. Changing only one coefficient changes the reaction ratios. The calculator does not balance the equation, so chemical consistency of the coefficients remains the user's responsibility. If the mass input includes an entire solution, establish pure reactant mass separately. A limiting reagent calculation gives a theoretical maximum. Equilibrium, side reactions, purity and product recovery can affect actual output. Reaction rate and safe operating conditions are not determined by this calculation.

Frequently asked questions

How do you calculate the limiting reagent with moles?

With example coefficients 2 for A, 1 for B and 2 for product, initial amounts 4 and 3 mol give limiting reactant A and theoretical product 4 mol. The smaller mole to coefficient ratio sets reaction extent, while actual yield, equilibrium and reaction safety are not established by this calculation.

Calculate with these values