Limiting reagent
A
The reactant that runs out first based on the balanced equation.
Reaction yield planning
Limiting Reagent and Yield Calculator
Find the limiting reagent, theoretical product mass, expected actual yield, excess reagent, and yield loss from stoichiometry inputs.
Stoichiometry inputs
Enter the amount of reactant A, the mass and purity of reactant B, the balanced-equation coefficients and the product molar mass.
Theoretical product
11.26 g
Maximum product mass if the limiting reagent is fully converted.
Expected actual product
9.233 g
Theoretical mass multiplied by the expected percent yield.
Yield summary
The limiting reagent controls theoretical yield. Compare expected actual product with yield loss to plan scale, purification and analytical checks.
Excess reagent remaining
0.239 mol
Excess remaining
79.29 %
Yield loss
2.027 g
Limiting extent
0.063 mol
Available B
0.302 mol
Overview
A limiting reagent and yield calculator helps connect a balanced chemical equation with practical laboratory quantities. In a reaction with two reactants, the limiting reagent is the one that runs out first after stoichiometric ratios are applied. It controls the maximum amount of product that can form. The other reactant remains in excess. This tool calculates the limiting reagent, theoretical product mass, expected actual product mass, excess reagent and yield loss.
The calculator is useful for teaching stoichiometry, planning small-scale syntheses, checking reagent purchases and preparing lab notebooks. It accepts reactant A directly in moles and reactant B as a weighed mass with molar mass and purity correction. That mirrors common lab work: one reagent may be prepared as a solution or known amount, while another is weighed as a solid with a stated assay.
How to use it
Enter the moles of reactant A. For reactant B, enter the weighed grams, molar mass and purity percentage. Then enter the stoichiometric coefficients from the balanced equation for A, B and the product you are tracking. Finally add the product molar mass and the expected percent yield. The percent yield should reflect workup, isolation and purification, not the theoretical stoichiometric maximum.
Formula and method
The calculator converts B to moles by multiplying mass by purity and dividing by molar mass. It divides each reactant amount by its stoichiometric coefficient. The smaller value is the limiting reaction extent. Product moles equal that extent multiplied by the product coefficient. Theoretical product mass is product moles times product molar mass. Expected actual mass is theoretical mass multiplied by percent yield.
Interpreting the results
The limiting reagent result tells which input controls the batch. Theoretical product is the best possible mass under complete conversion and perfect recovery. Expected actual product is usually the more realistic planning value. Excess reagent remaining helps identify whether a reagent is being wasted or deliberately used in excess to drive conversion. Yield loss shows the mass difference between ideal and expected recovery.
Practical example
Suppose a reaction uses 0.125 mol of A and 18 g of B with molar mass 58.44 g/mol at 98% purity. If the balanced equation consumes 2 mol of A for every 1 mol of B and produces 1 mol of product, A may become limiting. The product moles are based on A divided by 2. With a product molar mass of 180.16 g/mol, the theoretical product is about 11.26 g. At 82% yield, the expected isolated mass is about 9.23 g.
Limitations
This calculator assumes the balanced equation is correct and that only two reactants determine the limiting step. It does not model equilibrium, side reactions, solvent participation, catalysts, moisture sensitivity, gas evolution, heat transfer or analytical uncertainty. Purity corrections are only as good as the assay data. Use the result for planning and checking arithmetic, then confirm reaction design with chemical expertise and safe laboratory practice.