Question

When ethane is burnt in excess of air, the products of combustion are:
(a)- $C$ and ${{H}_{2}}O$
(b)- $CO$ and ${{H}_{2}}O$
(c)- $C{{O}_{2}}$ and ${{H}_{2}}$
(d)-$C{{O}_{2}}$ and ${{H}_{2}}O$

Answer 1

The general reaction of complete combustion of alkane is ${{C}_{n}}{{H}_{2n+2}}+\left( \dfrac{3n+1}{2} \right){{O}_{2}}\to nC{{O}_{2}}+(n+1){{H}_{2}}O$. In ethane, there are 2 carbon atoms.

Complete step by step answer:
Ethane is a member of the alkane group and it has 2 carbon atoms.
On heating, alkanes readily burn in air or oxygen producing carbon dioxide ($C{{O}_{2}}$) and water (${{H}_{2}}O$). This process is called combustion.
For example, Methane of combustion forms carbon dioxide and 2 moles of water. The reaction is:
$C{{H}_{4}}+{{O}_{2}}\to C{{O}_{2}}+2{{H}_{2}}O$
The general reaction of complete oxidation of alkane is:
${{C}_{n}}{{H}_{2n+2}}+\left( \dfrac{3n+1}{2} \right){{O}_{2}}\to nC{{O}_{2}}+(n+1){{H}_{2}}O$.
So, in ethane, the n is 2. So, the reaction is:
${{C}_{2}}{{H}_{6}}+\dfrac{7}{2}{{O}_{2}}\to 2C{{O}_{2}}+3{{H}_{2}}O$.
So, the products of complete oxidation of ethane are 2 moles of carbon dioxide, and 3 moles of water.

Hence, the correct answer is an option (d)- $C{{O}_{2}}$ and${{H}_{2}}O$.

Additional information: There are 2 more forms of oxidation of alkane:
(i)- Incomplete combustion: (a)- If the combustion of alkanes is carried out in a limited supply of air, carbon monoxide is formed with unburnt carbon in the form of carbon black or soot.
$2C{{H}_{4}}+3{{O}_{2}}\to 2CO+4{{H}_{2}}O$.
(b)- When the alkanes react with steam at 1273 K in the presence of nickel as a catalyst forming a mixture of carbon monoxide and hydrogen gas, is called syngas.
$C{{H}_{4}}+{{H}_{2}}O\xrightarrow{1273K,Ni}\underset{syngas}{\mathop{CO+3{{H}_{2}}}}\,$
(ii)- Catalytic oxidation: When a mixture of methane and oxygen (9:1 by volume) at a pressure of 100 atmospheres is passed through a copper tube at 573 K, methanol is formed.
$2C{{H}_{4}}+{{O}_{2}}\xrightarrow[Cu\text{ }tube]{100atm,573K}2C{{H}_{2}}OH$.

Note: The process of complete oxidation of alkane is accompanied by the liberation of a large amount of heat, therefore, alkanes which are the constituents of LPG, gasoline, kerosene oil, and diesel are used as fuels.