Law of Chemical Combination: Definition, Types, and Examples

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What is Law of Chemical Combination?

Chemistry is the study of the change of a substance from one form to the other.

These transformations frequently occur as a result of the combination of two diverse types of matter.

The combination of various elements to form compounds is ruled by certain basic rules. These rules are stated as laws of chemical combination.

The law of chemical combination describes the basic principles that are followed when atoms and molecules interact.

This remarkable variety of interactions allows for a diverse variety of chemical reactions and compounds.

Though chemical reactions are complex yet they are all primarily ruled by some guiding laws of chemical combination, which lay the basis for the investigation or analysis of chemical reactions.

Law of Chemical Combination Rule

The combination of elements to form compounds is ruled by the five basic laws which are mentioned below:-

1. Law of Conservation of Mass.

2. Law of Definite Proportions.

3. Law of Multiple Proportions.

4. Gay Lussac’s Law of Gaseous Volumes.

5. Avogadro Law.

1. Law of Conservation of Mass

In 1789, this law of conservation of mass was framed by Antoine Lavoisier. In simple terms, this law of conservation of mass states that matter can neither be created nor it can be destroyed.

In other words, the total mass, that is, the sum of the mass of reacting mixture that is the reactants and the products formed always remains constant.

For instance; the Burning of wood Thus, when wood burns the mass of the dust, ashes, and fumes is always equal to the original mass of the charcoal and the oxygen present when it initially reacted.

So the mass of the product which is ashes and gases equals the mass of the reactant which is charcoal and oxygen.

2. Law of Definite Proportions

A French well-known chemist, Joseph Proust stated that the proportion of elements by mass in a given compound will remain the same at all times.

In simple terms, This law of constant proportions states that chemical compounds are made up of elements that are present in a fixed ratio in terms of their masses.

For example; A nitrogen dioxide (NO2) molecule is taken, thus, the ratio of the number of nitrogen atoms and oxygen atoms present in a given compound is 1:2 always. This ratio of 1:2 between the molecules of nitrogen and oxygen would always remain the same.

3. Law of Multiple Proportions

In 1803, This law of multiple proportions which was given by Dalton stated that if two elements combine to form more than one compound, the masses of these elements present in the reaction are defined in the ratio of small whole numbers.

For instance, the masses of molecules of oxygen is combined with a fixed mass of carbon in CO2 (carbon dioxide ) and CO (carbon monoxide) are 32 and 16, respectively. Consequently, these masses of oxygen display a simple ratio of 32: 16 or it can be written as 2: 1.

4. Gay Lussac Law of Gaseous Volumes

In 1808, Gay Lussac gave this law built on his observations. In simple words, Gay Lussac law or Amonton’s law states that the pressure exerted by a gas is directly proportional to the temperature of the gas when the mass is fixed and the volume is kept constant.

The mathematical expression of the above-given law can be inscribed as follows:

P ∝ T;

P = kT


P/T = k

• P is as defined the pressure applied by the gas on the walls of its vessel

• T is defined as the absolute temperature of the gas

For example, when aerosol cans are kept under warm conditions they eventually burst, because by heating the aerosol can pressure of the contents increases ultimately causing the can to burst.

When a pressurized aerosol can for example a deodorant can or a spray-paint can is heated, the consequent increase in the pressure is applied by the gases on the walls of its vessel can result in a blast.

This is the reason why numerous pressurized bottles or vessels have alerting labels stating that the given vessel must be kept away from fire and should be stored in a cool atmosphere.

5. Avogadro’s Law

Avogadro anticipated this law in the year 1811. Avogadro’s law is a relationship between the volume of gas and the number of moles.

This law states that at a constant temperature and pressure the total number of atoms or molecules present in a gas is directly proportional to the volume employed by that gas.

This indicates that 4 litres of hydrogen will have the same number of molecules as 4 litres of oxygen assumed that both the gases are at the same temperature and pressure.

This equation is mentioned below;

V ∝ n

V= kn


k = V/n

V is defined as the volume of gas

n is defined as the number of moles present in a given gas

k is defined as the proportionality constant

For instance, A compressed pool tube becomes portable when the number of air particles inside the tube is decreased which in turn decreases its volume and makes it compact.

During inflation, when the tube is filled with air thus it increases the number of air molecules in it which in turn increases the volume and size of the pool tube.

Hereafter, Avogadro’s law can be useful to inflate or deflate the given pool tube as per our need.

Law of Chemical Combination Citations


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