The mole ratio is the ratio of the numbers of moles of substances in a reaction, read directly from the coefficients of the balanced equation and used to convert between amounts.
The mole ratio is the ratio of the numbers of moles of the substances in a reaction. It is read directly from the coefficients of the balanced equation, and it is used to convert between the amounts of different substances. Malay: nisbah mol · Chinese: 摩尔比.
Once an equation is balanced, its coefficients tell you the proportions in which the substances react and are produced, measured in moles. The mole ratio is the tool that lets you move from the amount of one substance to the amount of another, which is the whole point of a stoichiometry calculation. If a formula has no coefficient written in front, its coefficient is taken to be one.
Example. In the reaction 2H2 + O2 → 2H2O, the mole ratio of hydrogen to oxygen to water is 2:1:2. So four moles of hydrogen react with two moles of oxygen to give four moles of water. If you know that one mole of oxygen is used, the ratio tells you that two moles of hydrogen are needed and two moles of water form. The same ratio scales to any amount, so three moles of oxygen would need six moles of hydrogen and produce six moles of water.
Confusion to avoid. The mole ratio comes from the coefficients, not from the masses, so you cannot read it off by comparing grams; you must convert masses to moles first. Take care also not to mix up the mole ratio with the ratio of atoms inside a single formula, which is a different idea used for empirical formulae.
In this chapter the mole ratio is the pivot of stoichiometry: it links the balanced equation to the mole, and through the mole to mass and gas volume, making it one of the most powerful tools in SPM Chemistry.
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