There are five laws of chemical Combinations :
1. Law of Conservation of Mass: This law states that matter can neither be created nor be destroyed. In other words, the total mass, that is, the sum of mass of all reactants and the products formed remains constant. This law is also called as the law of indestructibility of matter. Example
2. Law of Definite Proportions: Joseph Proust, a French chemist stated that the proportion of elements by weight in a given compound will always remain exactly the same. In simple terms, we can say that, irrespective of its source, origin or its quantity, the percent composition of elements by weight in a given compound will always remain the same.
Example: A pure water obtained from which ever source or any country will always be made up of only hydrogen and oxygen elements combined together in the same fixed ratio of 1 : 8 by mass.
3. Law of Multiple Proportions: This law states that if two elements combine to form more than one compound, the masses of these elements in the reaction are in the ratio of small whole numbers. This law was given by Dalton in the year 1803.
For example, Hydrogen and Oxygen combine to form water H2O and hydrogen peroxide H2O2. Two atoms of hydrogen combine with one atom of oxygen in the case of water, while-two atoms of hydrogen combine with two atoms of oxygen in the case of hydrogen peroxide. The ratio of oxygen atoms combining with a fixed number of hydrogen atoms in these two compounds is 1 : 2.
4. Law of Reciprocal Proportion: This law states that “when two elements combine separately with third element and form different types of molecules, their combining ratio is directly reciprocal if they combine directly.”
5. Gay Lussac’s Law of Gaseous’Volumes: In 1808, Gay Lussac gave this law which states that when gases are produced or combined in a chemical reaction, they do so in simple ratio by volume given that all the gases are at same temperature and pressure.
Example: Combination between nitrogen and hydrogen: One volume of nitrogen always combines With 3 volumes of hydrogen to form two volumes of ammonia. This reaction also indicates a simple ratio of 1: 3 : 2 between the volume of the reactants and products.
