Question

State and explain laws of chemical combination.

Answer 1

Five laws of chemical combination exist in chemistry. They mainly focus on mass, volume and different proportions in which matter can exist. Some of them can be understood by a simple chemical reaction while others can be understood by the gas laws.

Complete answer:
There are total five laws of chemical combination in chemistry. We will go through each one of them one by one.
1. Law of Conservation of Mass:
First we have the Law of Conservation of Mass. This law states that matter can neither be created nor it can be destroyed. We can understand this better by taking the example of a simple chemical reaction.
$A + B \to C + D$
If masses of A, B, C and D are x, y, w and z grams respectively then the total mass of reactant that is $x + y$ will be equal to the mass of the product that is $w + z$ . The new mass produced in the reaction will be exactly equal to the mass of reactants neither less nor more.
2. Law of Definite Proportions:
The second law is Law of Definite Proportions. This law states that the proportion of elements by weight in a compound remains constant. For example, consider the compound water. Its molecular formula is ${H_2}O$ . The weight of water molecules is $18g$ . If we break this mass hydrogen contributes $2g$ and oxygen contributes $16g$ . The ratio of masses of oxygen and hydrogen is $16:2$ or $8:1$ . This ratio remains constant no matter how long the water molecule chain grows.
3. Law of Multiple Proportions:
The third law is the Law of Multiple Proportions. This law states that if two or elements combine to form a compound, the masses of these elements are in ratio of whole numbers.
4. Gay Lussac’s Law of Gaseous Volumes:
The fourth law is Gay Lussac’s Law of Gaseous Volumes. This law states that when gases combine in a reaction, they combine in a simple ratio by volume in a condition where all gases are at same temperature and pressure.
5. Avogadro’s Law:
The last law is Avogadro’s Law. This law states that in a closed container, equal volume of all gases containing equal number of moles given the condition of temperature and pressure are the same. For example, one litre of oxygen will contain the same number of moles as one litre of hydrogen at same temperature and pressure.

Note: Law of Definite Proportions is not applicable when an element exists in different isotopes. Law of conservation of Mass fails when a large amount of heat is absorbed or evolved during a chemical reaction.