Law of chemical combination:-
Chemical reactions take place according to cortain Law, called laws of chemical combination
There are:-
(1) Law of conservation of mass:-
=>This law was proposed by Antoine Lavoisier in 1789.
=>It states that,"In all physical and chemical change total mass of reactant is always equal to the total mass of product".
=>In another words "Matter Can neither be created nor be destroyed".
=>This law is used for balancing the chemical reactions.
(2) Law of constant proportion or Law of definite proportion
=>This law was given by "Joseph Proust" in 1799. It states that,
"A chemical compound always contain exactly the fixed proportion of elements by mass".
Eg:-(1) A sample of pure water (H2O) obtained from whatever the sources, it always contain the fixed proportion of H and O is 2:16 or 1:8 by mass.
Eg:-(2) A sample of CO2 can be prepared in laboratory.
(1) By combustion of carbon in excess of air.
(3) By the action of hydrochloric acid on marble
(4) By heating sodium bicarbonate
In all the above process the CO2 SO produced it contains the fixed proportion of C and O i.e 12:32 or 3:8 by mass.
(3) Law of Multiple proportion
This law was given by "John Dalton" in 1803. It states that "When two different elements combine with one another to form two or more than two compounds then the mass of one of the element which combines with a fixed mass of another element produces a simple whole no. ratio with each other by mass".
The ratio of masses of oxygen which combine with a fixed mass of carbon in CO and CO2 is 16:32 or 1:2 by mass
Eg:-(2) Nitrogen combines with oxygen and form following five oxides:-
The ratio of masses of oxygen in above oxide is 4:8:12:16:20 or 1:2:3:4:5 which is a whole no. ratio
(4) Law of reciprocal proportion:-
This law was given by Richter in 1792. According to this law "when two different elements combine with a fixed mass of third element, then the ratio of their masses in which they do so is either same or some whole no. multiple of the ratio when both combine with each other by mass".
For example:-(1) The ratio of masses of C and O in CH4 and H2O= 3:8-----------(1)
The ratio of masses of C and O in CO2=3:8--------(2)
Both the ratio (1) and (2) are the same
(2) The ratio of masses of C and S in CO2 and SO2= 12:32 or 3:8----------(1)
Again the ratio of masses of C and S in CS2=12:64 or 3:16------------(2)
Both the ratio (1) and (2) are related as:-
⅜:³/16=1:2 which is whole no.multiple of each other
(5) Law of Gaseous volume:
This law was presented by Gay Lussac in 1808.
According to this law, "Gases react with each other in a simple ratio of their volume and if the product is also in gasesous state then the volume of product produces a simple whole no. ratio with the volume of reacting gases at STP".
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