An immersion heater, in an insulated vessel of negligible heat capacity brings 10 g of water to the boiling point from `16^@C` in 7 min. Then The heat of vapourization of alcohol is

Options

A. `854 J//Kg`
B. `854xx10^(3) J//kg`
C. `204 cal//g`
D. `204 cal//kg`

Answer

B

Explanation

Heat required to vapourize it at `78^@C`
`Q_v=Pt_3=(20cal)(306s)`
If L is the heat vapourization of alcohol
`Q_v=m_3L`
`L=((20xx306)cal)/(30g)=204(cal)/(g)=854(J)/(g)`
`=854xx10^3(J)/(kg)`