Laws of chemical combination

Laws of chemical combination

Chemistry involves a lot of chemical reactions where a compound is formed by combining several elements. These chemical reactions involve several elements governed by the laws of chemical combination. There are five laws of chemical combination. This article attempts to explain all the laws of chemical combinations. 

Now imagine that you are learning to drive a car. The first thing you will know is all the rules to be followed while driving. There are some laws and regulations that govern how people drive their cars. Similarly, in chemistry, specific laws are followed while atoms are combined. 

Here are the five laws of chemical combination:

• Law of definite proportions
• Law of conservation of mass
• Avogadro’s Law of chemical combination
• Gay Lussac’s Law of gaseous volumes
• Law of multiple proportions

In this article, we will state the laws of chemical combinations.

Law of definite proportions

The Law of definite proportions was proposed by Joseph Proust in 1799. The Law of definite proportions is also known as the Law of constant proportion or Proust’s Law.

According to this Law, elements are combined in some definite proportion only. In other words, the elements are combined in a certain definite ratio irrespective of their source of origin or the total number of reactants.

For instance, ethyl alcohol: C2H50H

It doesn’t matter what the amount of ethyl alcohol is. It always comprises 52% carbon, 13% hydrogen, and 35% oxygen.

This is the Law of definite proportions.

Law of conservation of mass

Antonie Lavoisier proposed the Law of conservation of mass in 1789. This Law was proposed based on the results from several combustible reactions. 

According to this Law, mass cannot be created nor destroyed; mass can only be transferred from one form to another. 

It is a fundamental law in chemistry that can also be understood as the total mass of product obtained by the chemical combination equal to the sum of the mass of all the reactants involved. 

Let us use an example to understand this Law. 

If we heat 10 grams of calcium carbonate, we will get 5.6 grams of calcium oxide and 4.4 grams of carbon dioxide.

CaCO3 → CaO + CO2

We know that according to the Law of conservation of mass:

Mass of reactants = mass of products 

Thus according to this example,

Ten grams of calcium carbonate = 5.6 grams of calcium oxide + 4.4 grams of carbon dioxide.

10 = 5.6 + 4.4

Avagadro’s Law of chemical combination

Avogadro’s Law of the chemical combination was proposed in 1811 by Avagadro. 

According to this Law, the volume of gas molecules is directly proportional to the number of moles at a given pressure and temperature. It can be expressed as V ∝ n – equation (a)

Here V represents the volume of gaseous molecules and, 

n represents the number of moles.

Equation (a) can also be written as V = k x n

Here, k represents the proportionality constant. 

Thus, Avagadro’s Law of chemical combination state the following :

 V1/n1=V2/n2

Here 

V1 represents the volume of gas 1

n1 represents the number of moles in gas 1

V2 represents the volume of gas 2

n2 represents the number of moles in gas 2

This Law can also be understood with the help of an example. If helium is blown into a balloon, the volume or the size of the balloons starts increasing. Thus as the number of moles of gas increases in the balloon, its volume also increases.

Gay Lussac’s Law of gaseous volumes

Gay Lussac’s Law of gaseous volumes was propounded by Gay Lussac in 1808. 

According to this Law, the ratio of the volume of gaseous products and reactants can be represented in whole numbers. At a certain temperature and pressure, when gasses react, the ratio of the volume of its reactants and products can be represented in whole numbers. 

This Law can be understood with the help of an example. Hydrogen chloride gas, for instance, is governed by this Law:

H2 + Cl2 → 2 HCl

Here one volume of chlorine gas is combined with a volume of hydrogen gas to form two volumes of hydrogen chloride gas. Thus, 

hydrogen gas : chlorine gas : HCl = 1:1:2

Law of multiple proportions

The Law of multiple proportions was proposed by John Dalton in 1804. 

According to this Law, when two similar elements are combined to form multiple compounds, the masses of single elements combined with the similar mass of other elements exist in the ratio of whole numbers.  

This Law can be understood with the help of an example of oxygen and carbon atoms. Oxygen and carbon atoms are combined to form two products- carbon dioxide and carbon monoxide. In the case of carbon dioxide, 32.0 grams of oxygen is present for 12.0 grams of carbon atoms. In the case of carbon monoxide, 16.0 grams of oxygen is present for 12.0 grams of carbon. This ratio of carbon in carbon monoxide to the carbon in carbon dioxide is 32:16, which can be simplified to 2:1. 

Conclusion 

We have now covered all the laws of chemical combination, including the law of definite proportions, the law of conservation of mass, Avogadro’s law of chemical combination, Gay Lussac’s law of gaseous volumes and law of multiple proportions, along with their examples. Make sure to read the topic properly to understand all the laws properly.