Structural formula of ethanol is :$\mathrm{CH_3CH_2OH}$ When ethanol is heated with excess of conc. $\mathrm{H_2SO_4}$ at $443\,\mathrm{K}$ it results in the dehydration of ethanol to give ethene. $\,\underset{\text{Ethanol}}{\mathrm{CH_3CH_2OH}}\,\,\frac{\text{Conc. }\mathrm{H_2SO_4}}{43\,\mathrm{K}}\,\,\underset{\text{Ethene}}{\mathrm{CH_2}}=\mathrm{CH_2}+\mathrm{H_2O}$ Role of conc. $\mathrm{H_2SO_4}$ : Conc. $\mathrm{H_2SO_4}$ acts as a dehydrating agent which removes water from the ethanol.