🔥 Reactions Calculators

Stoichiometry, limiting reagents, theoretical yield, percent yield, and oxidation numbers.

All Reactions Tools

Stoichiometry Calculator Convert between moles of reactants and products using stoichiometric ratios. Limiting Reagent Calculator Identify the limiting reagent and excess reagent for a two-reactant reaction. Theoretical Yield Calculator Calculate the theoretical yield of a product from moles of limiting reagent. Percent Yield Calculator Calculate percent yield from actual and theoretical yield of a reaction. Oxidation Number Calculator Determine the oxidation state of elements in common ionic and covalent compounds.

Stoichiometry: The Mathematics of Chemical Reactions

Stoichiometry uses the balanced chemical equation to relate the amounts of reactants consumed and products formed. Every balanced equation contains mole ratios — the coefficients tell you how many moles of each substance participate. For the reaction 2H₂ + O₂ → 2H₂O, the mole ratio of H₂ to O₂ is 2:1, and the mole ratio of O₂ to H₂O is 1:2. To find how many moles of water form from 4 moles of hydrogen: 4 mol H₂ × (2 mol H₂O ÷ 2 mol H₂) = 4 mol H₂O. Converting between grams and moles using molar masses completes the calculation.

Limiting Reagent and Theoretical Yield

The limiting reagent is the reactant that runs out first and determines the maximum amount of product that can form. The excess reagent is the one present in greater quantity than needed. To identify the limiting reagent, calculate the moles of product each reactant would produce if it were completely consumed; the reactant producing less product is the limiting reagent. The theoretical yield is the calculated maximum mass of product, assuming the reaction goes to completion with no side reactions or losses. Actual laboratory yields are nearly always less than theoretical due to incomplete reactions, side reactions, and physical losses during transfer.

Percent Yield

Percent yield compares the actual amount of product collected to the theoretical maximum: % yield = (actual yield ÷ theoretical yield) × 100. A percent yield of 100% is ideal but rarely achieved. Industrial chemical processes aim for high percent yield to minimise waste and raw material costs. A synthesis reaction with 70% yield means 30% of the limiting reagent was lost to side reactions, incomplete conversion, or handling losses. Percent yield is also used to evaluate reaction conditions — changing temperature, pressure, catalyst, or solvent can substantially improve yield.

Oxidation Numbers and Redox Reactions

Oxidation number (oxidation state) is a bookkeeping tool that tracks electron transfer in chemical reactions. Rules for assigning oxidation numbers: elements in their pure form have oxidation number 0; hydrogen is +1 in most compounds (−1 in metal hydrides); oxygen is −2 in most compounds (−1 in peroxides); the sum of oxidation numbers in a neutral compound equals 0; in a polyatomic ion, the sum equals the ion charge. In a redox reaction, oxidation is an increase in oxidation number (loss of electrons) and reduction is a decrease (gain of electrons). The acronym OIL RIG (Oxidation Is Loss, Reduction Is Gain) helps remember the definitions.