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Calculate the change in internal energy ...

Calculate the change in internal energy when the 1 g water is converted into steam.

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Suppose, 1 g of water has to take for conversion into steam
Latent heat of vaporisation of water,
`L_V` =2256 J/g
`therefore DeltaQ`=2256 J/g
Volume of 1g water at atmospheric pressure is `1 "cm"^3` and its volume in vapour form is `1671 "cm"^3`.
Here, volume increases at constant atmospheric pressure = volume of vapour - volume of water
`therefore DeltaV=V_g-V_l` where , `V_g=1671 "cm"^3`
`V_l = 1 cm^3`
Work done at constant pressure ,
`DeltaW=PDeltaV=P(V_g-V_l)`
`=1.013xx10^5 [167xx10^6 -1 xx 10^(-6)]`
`=1.013xx10^5xx1070xx10^(-6)`
`approx` 169.2 J
From first law of thermodyanmics ,
`DeltaU=DeltaQ-DeltaW`
=2256-169.2
=2086.8 J
Hence, in the conversion of water into vapour, most of the heat is used for increasing its internal energy.
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