Law Of Constant Proportion

Law of Constant Proportion

Law of Constant Proportion

Every element combines to form compounds. They do so to become stable. It is found that these chemical combinations don’t occur in a random manner rather there are proper ways in which they combine and there are laws that are found to be true for the chemical combination. The laws that govern the chemical combination are known as laws of chemical combination:

  1. Law of conservation of mass

  2. Law of constant proportion

This article discusses the law of constant proportion – Statement and Indicative example.


“In a chemical substance, the elements are always present in definite proportions by mass”.

Even in earlier days, it was observed that many compounds contain two or more than two elements and each element was present in definite proportion irrespective of its source.

For e.g., If we take water from the river or from an ocean, both had oxygen and hydrogen in the same proportion.

An Indicative Example

In this section, we shall learn more about the topic with the simple example. Let us consider ammonia, every 17 gram of ammonia contains 14 gram of nitrogen and 3 grams of hydrogen irrespective of source. If we take 34 grams of ammonia, it will contain 28 gram of nitrogen and 6 grams of hydrogen. It’s clear that the ration by mass of ammonia, nitrogen, and hydrogen is always 17:14:3. Today with the concept of the atom, molecular mass, and molar mass already explained, this law of chemical combination is very obvious. But in the early age of chemistry, it was a major breakthrough. On the basis of this theory only, Dalton’s gave its postulates about its atomic structure which became the base for our understanding of the chemistry.

For more information about the concepts of chemical combinations and the different laws describing them and other related topics, download Byju’s- The learning app.


Practise This Question

Assertion : A future discovery of sub atomic particles led to the failure of Dalton’s atomic theory.

Reason : An atom is made up of protons, neutrons and electrons.