Explain how methane (ch4) and ethane (c2h6) demonstrate the law of definite composition and the law of multiple proportions

Law of definite composition: The elements which are present in the compound is combined in the same proportion by mass.

Law of multiple proportion: When two or more compounds are formed by the combination of two elements then the mass ratio of one element is combined with the fixed mass of the other element.

In case of methane, it consist of one carbon atoms and four hydrogen atoms implies that has definite composition. In terms of mass, in methane, carbon and hydrogen atoms are combined in a definite ratio i.e. 12 g C/ 4 g H. Thus, methane has definite composition.  

Now, carbon and hydrogen combines to give a class i.e. hydrocarbon. In this case, for every constant mass of carbon the ratio of hydrogen will always reduce to 4/3 ratio for the formation of ethane (hydrocarbon). Thus, law of multiple proportion followed.

Similarly, in case of ethane, this compound also consist of exact atoms but in different ratios.

In case of ethane, it consist of two carbon atoms and six hydrogen atoms implies that has definite composition. In terms of mass, in ethane, carbon and hydrogen atoms are combined in a definite ratio i.e. 24 g C/ 6 g H. Thus, methane has definite composition.  

Now, carbon and hydrogen combines to give a class i.e. hydrocarbon. In this case, for every constant mass of carbon the ratio of hydrogen will always reduce to a specific ratio for the formation of methane (hydrocarbon). Thus, law of multiple proportion followed.

Methane and ethane demonstrate the law of definite composition and the law of multiple proportions as these both compounds have the exact atoms but in different ratios.  

As for methane, it can be seen that every methane molecule contains 4 hydrogen atoms and 1 carbon atom. Where masses of carbon and hydrogen are in ratio - 12 g C / 4 g H -- reduce to 3g C/ 1 g H .

Ethane contains 2 carbon atoms and 6 hydrogen atom and their mass ratio will be  - 24 g C / 6 g H -- reduce to 4 g C/ 1 g H .

So both ethane and methane demonstrate the law of definite composition and the law of multiple proportions.

in 1783 cavendish was working with his hydrogen gas and found that when he burned it and condensed the vapor it was water. this was very significant since it disproved the greek theory of elements completely since water was not a simple substance but the product of two gases. it was lavoisier who hearing of the experiment gave cavendish's gas the name hydrogen ("water-producer") and added that hydrogen burned by combining with oxygen and that water was a hydrogen-oxygen combination.

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