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What is Stoichiometry?

A good command on stoichiometry can help students deal with variety of mathematical problems in chemistry. Here is more information about the same...
ScienceStruck Staff
Once you're able to understand stoichiometry, you'll be pleasantly surprised to discover that mathematics has a major role to play in different branches of chemistry. Derived from the Greek word, stoicheion (element) and metron (measure), stoichiometry is one of the most interesting branches of industrial chemistry. It is a quantitative relation of reactants and products in a chemical reaction, and is used in numerous calculations in industrial chemistry.


The basic principle on which stoichiometry works is that all chemical elements react in a particular way. We know that acids and bases react to give salt and water. We're aware of the fact that certain combustion reactions occur majorly in the presence of oxygen. Since in depth study in chemistry has helped us to predict the possible course of a chemical reaction, we can calculate the measure of reactants and products in a chemical reaction, as per industrial requirements.

To understand stoichometry, consider the example of formation of a water molecule. We know that hydrogen and oxygen are required to form water under some fixed conditions of temperature and pressure. With the help of stoichiometry, we can predict how much water will be formed if we know the measure of oxygen and hydrogen gases. In fact, with the help of balanced equations, we can calculate several unknown figures in a chemical reaction, provided we're aware of the value of some quantities. Mostly, all quantities in a chemical reaction are measured in terms of mole, as it makes complex mathematical calculations much simpler. An understanding of stoichiometry will be incomplete without knowing the most-used chemistry term, the mole.

As per international definitions, a mole is defined as the amount of substance that contains as many elementary particles (this includes atoms, molecules, ions, electrons), as there are atoms in 12g of the isotope carbon-12 (12C). The number of particles in one mole of a substance is called the Avogadro number and it equals to 6.02214179(30)×10-23. Generally, four vital conversions are used in stoichiometry.
  • Moles to grams
  • Moles to moles
  • Grams to moles
  • Grams to grams
Working of Stoichiometry

A good way to understand stoichiometry is to know the fundamental principles on which it works. Stoichiometry works on three major laws that are the basis of all laws and rules regarding mathematical calculations in a chemical reaction.
  • Law of Conservation of Mass: In an isolated or closed system, the mass of reactants in the beginning must be equal to the mass of the products in the end.
  • Law of Definite Proportions: Also known as Proust's law, the law of definite proportions states that any chemical compound always contains the same proportions of elements by mass.
  • Law of Multiple Proportions:Discovered by John Dalton in 1803, the law of multiple proportions forms the basis of modern-day stoichiometry. This law states that when chemical compounds combine in any reaction, they do so by combining in ratio of small whole numbers.
Stoichiometry is easier to grasp if students are able to understand the concepts of mole fraction, molarity equation, and similar other concepts of physical chemistry. Also, a good command over balancing equations is the key to understand maths in chemistry.