Question

Standard vaporisation enthalpy of benzene at its boiling point is 30.8 kJ mol^-1 ; for how long would a 100W electric heater has to operate in order to vaporise a 100g sample of benzene at its boiling temperature?

$open square brackets Power space equals space energy over time. space 1 straight W space equals space 1 space Js to the power of negative 1 end exponent close square brackets$

Name: Wired Faculty - The Best Learning App
Rating: 4.6 (1864 reviews)

Solution

increment subscript vap straight H to the power of 0 space for space benzene space equals space plus 30.8 space kJ space mol to the power of negative 1 end exponent Molar space mass space of space benzene space left parenthesis straight C subscript 6 straight H subscript 6 right parenthesis space equals space 78 straight g space mol to the power of negative 1 end exponent No. space of space moles space in space 100 space straight g space of space benzene space left parenthesis straight n right parenthesis space equals space 100 over 78 Heat space supplied space left parenthesis straight q right parenthesis space equals space straight n space cross times space increment subscript vap straight H to the power of circled dash space space space space space space space space space space space space space space space space space space space space space space space space space equals space 100 over 78 mol space cross times space left parenthesis 30.8 space kJ space mol to the power of negative 1 end exponent right parenthesis

= 39.487 kJ
= 39487 J
Now, Power = 100 W = 100 Js^-1But ,

Power space equals space Energy over Time

therefore space space space space Time space equals space Energy over Power space equals fraction numerator 39487 straight J over denominator 100 space Js to the power of negative 1 end exponent end fraction space space space space space space space space space space space space space space equals space 394.87 space straight s space space space space space space space space space space space space space space equals space fraction numerator 394.87 over denominator 60 end fraction min space equals space 6.6 space min

For Daily Free Study Material Join wiredfaculty