Question

How much heat is evolved when 1234 g of water condenses to a liquid at 100.°c?

Answer 1

During the phase transition vapour --> liquid water, the temperature of the water does not change; the molecules of water release heat and the amounf of heat released is equal to

`Q=mL_e`
where
m is the mass of the water

`L_e` is the latent heat of evaporation.

For water, the latent heat of evaporation is
`L=2257 kJ/kg`, while the mass of the water is

`m=1234 g=1.234 kg`

so, the amount of heat released in the process is

`Q=mL_e = (1.234 kg)(2257 kJ/kg)=2785 kJ`