Asample of chloroethane, c2h5cl, absorbs 0.185 kj and begins to vaporize at its normal boiling point of 12.3°c. what is the mass of the chloroethane sample? the molar heat of vaporization for chloroethane is 24.7kj/mol.

Heat absorbed (q) = 0.185 kJ
Molar heat of vaporization (ΔH) = 24.7 kJ/ mol
Molar mass of chloroethane = 64.51 g/mol
q = (ΔH) * (n) where n is the number of moles.
so n = q / ΔH = 0.185 / 24.7 = 7.5 x 10⁻³ mole
number of moles = mass(g) / Molar mass
mass (g) = number of moles * molar mass 
               = (7.5 x 10⁻³) * (64.51) = 0.48 g  

Its a hope this