Question

Calculate the enthalpy of vaporisation of ethanol if 11.5 g of ethanol is completely vaporised by supplying 11.8 kJ of heat.

विकल्प

• 21.7 kJ mol^-1

• 47.2 kJ mol^-1

• 65.1 kJ mol^-1

• 39.0 kJ mol^-1

Answer 1

47.2 kJ mol^-1

Explanation:

Molar mass of ethanol (C₂H₅OH)

= (2 × 12.01) + (6 × 1.008) + (1 × 16.00)

= 46.08 g mol^-1

\[\text{Number of moles}=\frac{\mathrm{Given~mass}}{\mathrm{Molar~mass}}\]

\[=\frac{11.5\mathrm{g}}{46.08\mathrm{gmol}^{-1}}\] = 0.25 moles

Total heat supplied = 11.8 kJ

∴ Enthalpy of vaporization (ΔH_vap )

\[=\frac{\text{Heat supplied}}{\text{Number of moles}}=\frac{11.8\mathrm{kJ}}{0.25\mathrm{moles}}=47.2\mathrm{kJ~mol}^{-1}\]