Question

Cracking of ethane gives a mixture of .

• A. ${\mathrm{CH}}_2={\mathrm{CH}}_2+{\mathrm{CH}}_4+H_2$
• B. ${\mathrm{CH}}_4+H_2$
• C. ${\mathrm{CH}}_2={\mathrm{CH}}_2+H_2$

Answer 1

The correct option is A ${\mathrm{CH}}_2={\mathrm{CH}}_2+{\mathrm{CH}}_4+H_2$

Alkanes on heating to higher temperature decompose into lower alkanes, alkenes etc. Such decomposition reaction into smaller fragments by the application of heat is called cracking. On thermal decomposition ethane gives a mixture of ethene, methane, hydrogen gas. It takes place as follows:
$\mathrm{Initiation}:{\mathrm{CH}}_3-{\mathrm{CH}}_3\to 2{{\mathrm{CH}}_3}^{\bullet }\mathrm{Propagation}:i){\mathrm{CH}}_3-{\mathrm{CH}}_3+{{\mathrm{CH}}_3}^{\bullet }\to {\mathrm{CH}}_4+{\mathrm{CH}}_3-{{\mathrm{CH}}_2}^{\bullet }(\mathrm{methane}\left)\mathrm{ii}\right){\mathrm{CH}}_3-{{\mathrm{CH}}_2}^{\bullet }\to {\mathrm{CH}}_2={\mathrm{CH}}_2+H^{\bullet }\left(\mathrm{ethene}\right)\mathrm{Termination}:H^{\bullet }+H^{\bullet }\to H_2\left(\mathrm{hydrogen}\right)$