A swimmer coming out from a pool is covered with a film of water weighing about 80 g. How much heat must be supplied to evaporate this water?

Solution

The process of evaporation can be represented as:

stack 80 straight g space straight H subscript 2 straight O with left parenthesis Liquid right parenthesis below space space space space rightwards arrow with Vaporization on top space stack 80 gH subscript 2 straight O with left parenthesis Vapour right parenthesis below

Now space increment subscript vap straight H to the power of 0 space for space water space equals space plus 40.79 space kJ space mol to the power of negative 1 end exponent Molar space mass space of space water space equals space 18 space straight g space mol to the power of negative 1 end exponent Number space of space moles space in space 80 space straight g space of space water left parenthesis straight n right parenthesis space equals space fraction numerator 80 straight g over denominator 18 straight g space mol to the power of negative 1 end exponent end fraction space equals space 4.44 space mol

therefore space space 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 0 space space space space space space space space space space space space space space equals left parenthesis 4.44 space mol right parenthesis space cross times space left parenthesis 40.79 space kJ space mol to the power of negative 1 end exponent right parenthesis space space space space space space space space space space space space space space equals 1.81 space cross times space 10 squared space kJ

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