It takes much longer to boil off a certain quantitty of water than to bring it to its boiling pointfrom room temp.

Asked by lovemaan5500 | 26th Nov, 2017, 12:37: PM

Expert Answer:

This is due to latent heat of vapourisation of steam. Latent Heat of vapouraisation of steam is the heat energy required for
water to change its liquid state at boiling point 100°C to vapour state at 100°C. For water this energy is 22.5 x 105 J/kg.
For example if 1 kg of water is boiled from room teperature, say 25ºC to 100ºC, heat energy required is 1× 4200 ×(75) = 3.15 × 105 Joules.
For the same 1 kg water, heat energy required to undergo the change of state at boiling point 100 ºC, from liquid state at 100°C to vapour state 100°C is 22.5 × 105 Joules.
Hence if heat energy is supplied at same rate, it takes longer time for the water to get boiled off

Answered by  | 27th Nov, 2017, 11:14: AM