0.6667
: 1
1.5
: 1
1
1.5
0.6667
: 1
1.5
: 1
1
1.5
The Molar Ratio Calculator determines the ratio of moles between two substances in a chemical reaction or mixture. The molar ratio is a core concept in stoichiometry derived from the coefficients of a balanced chemical equation. It tells you the exact proportions in which reactants combine and products form. For example, in the reaction 2H2 + O2 -> 2H2O, the molar ratio of H2 to O2 is 2:1. This calculator accepts the moles of two substances and returns their ratio in multiple formats: as a decimal relative to each substance, and as a simplified whole-number ratio. It is indispensable for limiting reagent determination, yield calculations, empirical formula derivation, and reaction scaling.
The molar ratio between two substances is simply:
Ratio = n1 / n2
This calculator provides several representations:
Common uses of molar ratios:
The simplified ratio normalizes the smaller value to 1, making it easy to see the relationship (e.g., 1:1.5 or 1:2). For stoichiometric applications, you typically want whole-number ratios. If the simplified ratio gives values like 1:1.5, multiply both by 2 to get 2:3. The decimal ratio formats are useful for precise calculations and for determining whether reactant quantities match the required stoichiometric proportions.
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4 mol H2 to 2 mol O2 gives a ratio of 2:1, matching the stoichiometric coefficients in 2H2 + O2 -> 2H2O. The reactants are in perfect stoichiometric proportion.
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C:H ratio = 1.5:3 = 1:2. The empirical formula is CH2 (found in alkenes like ethylene C2H4). Multiply both by 2 if the molecular formula has a higher mass.
The coefficients in a balanced chemical equation directly give the molar ratios. In 2Al + 3Cl2 -> 2AlCl3, the molar ratio of Al to Cl2 is 2:3, Al to AlCl3 is 2:2 (or 1:1), and Cl2 to AlCl3 is 3:2.
Divide the actual moles of each reactant by its stoichiometric coefficient. The reactant with the smallest result is the limiting reagent. For example, if you have 5 mol A and 4 mol B for A + 2B -> C, then A gives 5/1 = 5, B gives 4/2 = 2. B is limiting.
For empirical formulas, round to the nearest whole number if close (e.g., 1.98 rounds to 2). If the ratio is close to a simple fraction (like 1.33 or 1.5), multiply all values by 3 or 2 respectively to get whole numbers.
Yes. For ideal gases at the same T and P, the molar ratio equals the volume ratio (Avogadro's Law). So if 2 volumes of H2 react with 1 volume of O2, the molar ratio is 2:1.
Molar ratio compares moles of one substance to another (n1:n2). Mole fraction compares moles of one substance to the total moles (n1/(n1+n2)). They express related but different information about composition.
To scale a reaction, multiply all reactant and product moles by the same factor. If the original reaction uses 2 mol A and 1 mol B, scaling by 5 requires 10 mol A and 5 mol B, maintaining the 2:1 ratio.
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