Termodynamics: heat supplied with loss of mass

[libelec]

Homework Statement

Find the mass of liquid lead at fussion temperature needed to heat up 1kg of liquid water from 20ºC to 60ºC, considering P = 1 atm, and a loss of 100 mg of water due to local vaporization.

My question is: what do I do with that loss of mass? Do I calculate Q for m = (1000 - 0,1) g?

I'm really at loss with that.

Thanks.

 

[Borek]

Final mass of water is 1kg-100mg, no doubt about it. Question is whether heat of vaporization should be taken into account or not in heat balance. However, check if it matters - we are talking about 10^-4 of the initial mass, most likely difference will be way below accuracy of the final result.

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[libelec]

Yes, apparently I had to use that mass to calculate heat through the change of phase equation: Q = m*(delta)H.

Thanks.