Stoichiometry Calculator
Calculate mole ratios, mass-to-mass conversions, limiting reagents, theoretical yields, and percent yields for balanced chemical reactions. Enter reactant amounts to determine product quantities — essential for chemistry students, lab technicians, and chemical engineers.
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What is Stoichiometry?
Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction, governed by the balanced chemical equation. The coefficients in a balanced equation represent mole ratios: in 2H₂ + O₂ → 2H₂O, two moles of hydrogen react with one mole of oxygen to produce two moles of water. These ratios enable calculation of exact reactant and product quantities.
Stoichiometric calculations are fundamental to chemistry — they determine how much of each reactant is needed, which reactant runs out first (limiting reagent), how much product can theoretically be formed (theoretical yield), and how efficient the reaction was (percent yield). This calculator handles all these calculations from the mole ratios you provide.
使用される計算公式・方程式
この計算ツールは5つの主要な公式を使用しています：
1 Mole Ratio Conversion ▼
For 2H₂ + O₂ → 2H₂O: 3 moles H₂ produces 3 × (2/2) = 3 moles H₂O.
2 Moles from Grams ▼
36 grams of water (H₂O, MW=18): Moles = 36 / 18 = 2 moles.
3 Theoretical Yield ▼
Determines the maximum possible product from the limiting reagent.
Explore all calculation options on the 比率計算ツール home page.
比率計算ツールの使い方
この比率計算ツールは、以下の3ステップで簡単にご利用いただけます：
数値を入力
入力欄に既知の比率の値を入力します。求めたい未知数の入力欄は空欄のままにしておきます。
モードを選択
比率モード（解く、簡素化、スケーリング）を選択します。各モードで異なる計算式が適用されます。
結果を確認
計算するボタンを押します。結果画面に答えと、視覚的な比率バー、円グラフ、詳細なステップバイステップの解決プロセスが表示されます。
実例問題と段階的な解説
本比率計算ツールを使って、以下の3つの例題をステップバイステップで解決するプロセスです：
入力 1 How much O₂ needed to react with 4 moles H₂?
入力 2 Theoretical yield from 10g CH₄ burning in excess O₂
入力 3 Find limiting reagent: 5 mol H₂ and 4 mol O₂
よくある質問 (FAQ)
What is stoichiometry? ▼
Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions. It uses the coefficients in balanced equations to determine mole ratios, which enable calculation of how much of each substance is needed or produced.
How do I calculate moles from grams? ▼
Moles = Mass (grams) ÷ Molar Mass (g/mol). For example, 36g of water (H₂O): Molar mass = 2(1.008) + 16.00 = 18.016 g/mol. Moles = 36 ÷ 18.016 = 2.0 moles. The molar mass is the sum of atomic masses of all atoms in the formula.
What is a limiting reagent? ▼
The limiting reagent is the reactant that is completely consumed first, determining the maximum amount of product that can form. The other reactant(s) are in excess. To find it: convert all reactants to moles, divide each by its coefficient — the smallest value indicates the limiting reagent.
What is theoretical yield? ▼
Theoretical yield is the maximum amount of product that can be formed from the limiting reagent, assuming 100% conversion and no losses. It is calculated using stoichiometry: moles of limiting reagent × mole ratio × product molar mass.
What is percent yield? ▼
Percent yield = (Actual Yield ÷ Theoretical Yield) × 100. It measures reaction efficiency. Real reactions rarely achieve 100% due to side reactions, incomplete conversion, and purification losses. A 90%+ yield is considered excellent in most contexts.
How do I use mole ratios? ▼
Mole ratios come from balanced equation coefficients. In 2H₂ + O₂ → 2H₂O, the ratio of H₂ to O₂ is 2:1, and H₂ to H₂O is 2:2 (1:1). To find moles of product: moles of reactant × (product coefficient ÷ reactant coefficient).
What is the molar mass and how do I find it? ▼
Molar mass is the mass of one mole of a substance in grams. Find it by adding the atomic masses (from the periodic table) of all atoms in the formula. NaCl: 22.99 + 35.45 = 58.44 g/mol. Ca(OH)₂: 40.08 + 2(16.00) + 2(1.008) = 74.10 g/mol.
How do stoichiometry and the conservation of mass relate? ▼
The conservation of mass states that matter is neither created nor destroyed. Stoichiometry ensures this is satisfied: the total mass of reactants equals the total mass of products. A balanced equation guarantees equal atoms on both sides, which guarantees equal mass.
Can I do stoichiometry with volumes of solutions? ▼
Yes. For solutions, moles = Molarity (mol/L) × Volume (L). A 0.5M HCl solution in 0.250L contains 0.125 mol HCl. Use this moles value in stoichiometric calculations just like moles calculated from mass.
What is excess reagent? ▼
The excess reagent is the reactant that remains after the limiting reagent is fully consumed. The amount of excess remaining = initial moles − moles consumed (calculated stoichiometrically from the limiting reagent). Converting this to grams gives the mass of unreacted excess.