Is the time taken for evaporation and melting of a given substance the same? Say that heat is being supplied at the same rate in both cases.(take substance as water)
1
-
$\begingroup$ Don't you think it depends on how rapidly heat is being supplied to the substance? If it were being supplied at the same rate, which do you think would happen faster, given that the heat of fusion is much less than the heat of vaporization? $\endgroup$– Chet MillerCommented Feb 16, 2017 at 11:42
Add a comment
|
3 Answers
$\begingroup$
$\endgroup$
The melting enthalpy of water/ice at $0°C$ is about $333.7 \frac{kJ}{kg}$, while the evaporation enthalphy of water at $100°C$ is about $ 2257 \frac{kJ}{kg} $, so with the same rate of heat supplied it would take longer to evaporate it than melt it.
$\begingroup$
$\endgroup$
For melting and for boiling there are energy barriers to overcome where you must supply "latent heat" to overcome the phase change. At this point the extra heat you add doesn't increase the temperature, but instead begins to melt or evaporate the substance.
The ratio of required heat to mass is called the Enthalpy of fusion when melting (or freezing) and the Enthalpy of vaporization when it's evaporating (or condensing).
For water, the enthalpy of fusion is almost 10 times the enthalpy of vaporization. If heat is being supplied at the same rate (as your edit says and I would have used as my stated assumption anyways) then you will require approximately 10x as much heat to vaporize the same mass than to melt it. It should therefore take 10 times as long if you can supply a constant heat.
$\begingroup$
$\endgroup$
For a solid to melt, you need to supply some energy to break the bonds in the solid. This energy is known as latent heat of fusion.
For a liquid to vaporize, you need to supply some energy to break the bonds in the liquid even further. This energy is known as latent heat of vaporization.
However, evaporation is a different phenomenon. During the process of evaporation, the molecules take energy from the adjacent atoms or surroundings to escape. The time taken for evaporation depends on various factors including humidity and surface area.
If you meant vaporization instead evaporation, the latent heat of vapourization and latent heat of fusion are different. Therefore, they will take a different amount of time if you supply energy at a constant rate for both the cases.
