Law of Stoichiometry

There are five laws of stoichiometry which are basis for understanding fundamental concepts of chemistry. Those five laws are:

  • Law of conservation of mass
  • Law of constant or definite proportions
  • Law of multiple proportions
  • Law of equivalent or reciprocal proportions
  • Law of gaseous volume

Law of conservation of mass

It states that total mass of reactant is equal to total mass of product or simply put  any substance that undergoes chemical reaction will have same mass throughout the reaction.It explains why chemical compounds are balanced.

Law of constant or definite proportions

It states that ” the mass ratio of element in any given same chemical compound will remain same whatever the method of preparation or its origin”. For example:

In these two chemical equations ,CO2   or Carbondioxide is produced.Whatever the mothod of preperation CO will always have mass ratio 12:32.

Law of multiple proportions

It states that ” when two or more than two elements combine to form two or more than two chemical compound the mass ratio of element with constant weight of other element will be in simple multiple proportions”. When Hydrogen and oxygen combine with each other they will form Water or Hydrogen peroxide.

Here mass ratio of H2:O = 2:16

Here mass ratio of H2:O2 = 2:32

so mass ratio of O:O2 = 16:32 (which is in simple multiple proportions)

Law of equivalent proportions

It states that “when two different elements combine with third element the mass ratio of those two elements will be same or in multiple proportion with mass ratio when they combine with each other.Taking three elements Hydrogen, Sulphur and Oxygen we can produce H2S,H2O and SO2.

mass ratio of H2S= 2:32
mass ratio of H2O= 2:32
since H2 is constant mass, ratio of S:O=32:32

mass ratio of SO2= 32:32
it is proved that S:O ratio = mass ratio of SO2

Law of Gaseous volume
It states that ” At normal temperature and pressure if two gases combine and produce gas as a product then their volume ratio will be in simple multiple proportions.


This is Ashish Thapa. It's just a name after all. Just had a thought that our names should signify our situation and should be dynamic. What if our name upgraded with respect to experiences acquired.

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