LAWS OF CHEMICAL COMBINATIONS 

Law of Conservation of Mass 

(Given by Antoine Lavoisier in 1789). It states that matter (mass) can neither be created nor destroyed. 

Law of Definite Proportions or Law of Constant Composition:

This law was proposed by Louis Proust in 1799, which states that: 'A chemical compound always consists of the same elements combined together in  the same ratio, irrespective of the method of preparation or the source from where it  is taken'. 

Law of Multiple Proportions 

Proposed by Dalton in 1803, this law states that:

'When two elements combine to form two or more compounds, then the different  masses of one element, which combine with a fixed mass of the other, bear a simple  ratio to one another'. 

Gay Lussac’s Law of Gaseous Volumes 

(Given by Gay Lussac in 1808.) According to this law when gases combine or are produced in a chemical reaction  they do so in a simple ratio by volume provided all gases are at same temperature and  pressure. 

e.g.H₂(g) + Cl₂(g) ---→2HCl(g) 

1V 1V 2V 

All reactants and products have simple ratio 1:1:2. 

Avogadro Law 

(In 1811, Given by Avogadro) 

According to this law equal volumes of gases at the same temperature and pressure  should contain equal number of molecules. 

Dalton's Atomic Theory 

All substances are made up of tiny, indivisible particles called atoms. Atoms of the same element are identical in shape, size, mass and other  properties. Atoms of different elements are different in all respects. 

Atom is the smallest unit that takes part in chemical combinations. Atoms combine with each other in simple whole number ratios to form  compound atoms called molecules. Atoms cannot be created, divided or destroyed during any chemical or physical  change.