Stoichiometric calculations

Once the reaction equation is balanced we usually want to use it to calculate amount of reagents that take place in the reaction. Sometimes we want it to be able to evaluate stoichiometric amount of reagents needed for some chemical process, sometimes we want to use it for the calculation of the titration (determination) result - regardless of the reason, we have to perform a stoichiometric calculation.

Information presented in the balanced chemical reaction equation describes reaction, not in terms of masses of the reagents, but in terms of numbers of molecules or moles. We can read the balanced reaction equation

2H2 + O2 → 2H2O

as "two diatomic molecules of hydrogen reacting with one diatomic particle of oxygen, creating two particles of water" or "two moles of diatomic hydrogen reacting with one mole of diatomic oxygen, creating two moles of water". What is important is the fact, that the ratio of the reagents stays constant - so if we take 1 mole of the hydrogen it will react with 0.5 moles of the oxygen, if we take 4 moles of oxygen, it will react with 8 moles of hydrogen and so on - number of moles of hydrogen reacting will be always twice the number of moles of oxygen, number of moles of oxygen reacting will be always half of the number of moles of hydrogen. It also means if there is only one mole of oxygen, it will never react with more than two moles of hydrogen - no matter how much hydrogen is present, only two moles can be consumed. If there is one mole of hydrogen, it will never react with more than half mole of oxygen, no matter how much oxygen is present.

While the stoichiometric information in the reaction equation is based on moles, it can be easily converted to masses - with the use of molar masses.

There are two basic methods of performing stoichiometric calculations - one is based on ratios and proportions of reagents, and the second on so-called dimensional analysis (which is not the best name, as dimensional analysis is also a much more complicated and advanced method, used for completely different purposes).

Note that our EBAS - equation balancer and stoichiometry calculator - performs all stoichiometric calculations instantly, saving you time.

Balancing & stoichiometry

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