Talk:Latent heat
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[edit] Error in data from external link
As far as I can tell, (at least some of) the data in the external link "Latent Heat of Melting for some common Materials" (http://www.engineeringtoolbox.com/latent-heat-melting-solids-d_96.html) is quite wrong!
This is underscored by the page having a "Related" link near the bottom labeled "Melting and Boiling Temperatures - Evaporation and Melting Heat" (http://www.engineeringtoolbox.com/melting-boiling-temperatures-d_392.html) which has different values for some of the same entities! This is two pages on the same site!!
It seems to clearly make the source questionable.
I would have mailed the webmaster of engineeringtoolbox, but I can't find a contact link.
Example: The "latent heat of of melting" for Copper is listed as 176 kJ/kg (or 75.6 Btu/lb, haven't checked this). On the related page, it is listed as 207 kJ/kg.
(NB: From http://www.webelements.com/webelements/elements/text/Cu/heat.html I get the enthalpy of fusion for Copper as 13,1kJ/mol. Divided by the molar weight of 63.546 gram/mol this yields 206kJ/kg, so the value on the page linked from this wiki page is probably NOT right (but the one on that page's related link is).
I suggest that the link be removed, and I will do so now (this is my first attempt at editing an Wiki, if you disagree with my edit, feel free to undo my changes)
In other news: This page seems to be almost completely redundant with Heat_of_vaporization and Heat_of_fusion (the first two links in See Also), why not move the few pieces not found there, and change this page into a pure disambiguation? Again, I'm hardly the expert on things Wiki.
BTW: Latent_heat_of_fusion and Latent_heat_of_vaporization redirects to the same pages as the two links above, and would more clearly indicate the relationsship with this page.
- Richard - 83.91.35.211 22:26, 11 April 2007 (UTC)
[edit] Query '04
Am I correct to question the "i.e. Temperature" part of the article?
Dylan Shell 09:22, 12 Jul 2004 (UTC)
- From my admittedly limited understanding, I believe you are correct. I'll remove your commentary and the reference to temperature and instead wikify internal energy. Thanks for bringing that up, and welcome to Wikipedia! -- Hadal 09:36, 12 Jul 2004 (UTC)
I am a little confused. According to the article, it says solid to gas is endothermic whereas gas to solid to exothermic. Shouldn't it be the other way round?
Dan
Look at it from the point of view of the solid sublimating or liquid evaporating. That material must absorb energy to change phase from solid->liquid->gas. It absorbs energy from its surroundings (cooling them) and is thus in an endothermic process.
Alex. 05:08, 5 August 2006 (UTC)
[edit] Latent heat as a function of pressure/temperature
Does the latent heat of a substance change as the pressure increases? Presumably past the critical point it is 0, does it move steadily towards 0 as we move up the gas-liquid curve, or does it drop off non-linearly? njh 11:18, 6 December 2005 (UTC)
- I believe the latent heat of fusion will increase/decrease dependent on the expansion/contraction during the fase change between solid and liquid. Ie. an expansion will do work on the surroundings, and this work will be higher at higher ambient pressure.
- Most materials contract during freezing - but water is an example of the opposite - it expands during freezing, which is why ice floats on water (expanding means lowering the density). This is a very lucky property of water - otherwise the ocean ice would be at the bottom of the ocean instead of floating - which I hear would prohibit life as we know it (not sure why).
- As far as I know vaporization always leads to expansion, so the latent heat of vaporization should at first look always increase with temperature. This however is not the case (as you say, at the critical point latent heat of vaporization is zero), because the expansion will be smaller faced with a higher pressure.
- The two effects works in opposite directions, so the net effect will not be linear. At zero pressure the work will be zero because there is no force, and at the critical pressure the work will be zero again because there is no expansion. In between the expansion will do positive work during vaporization. For freezing/melting the relationship should be almost linear as neither the volume of solids nor liquids are significantly affected by pressure (NB: This is by logic only, I didn't go look it up, so I might be wrong) - Richard - 83.91.35.211 22:26, 11 April 2007 (UTC)
[edit] Latent heat and global warming
Has anyone calculated the amount of latent heat required to melt the icecaps? And what about the time it may take to absorb all that latent heat.. How far has the process gone? Gregorydavid 15:57, 1 May 2006 (UTC)
[edit] Section line
the line under one of the sections cuts into the template on the right (at least in firefox). Is there a clean way to make the line shorter? Ojcit 21:08, 2 October 2006 (UTC)
[edit] Latent heat of vaporization for water
http://en.wikipedia.org/wiki/Kelvin_temperature_scale
- Water’s boiling point 373.1339 K
Enthalpy (kJ/kg):
- Vapor = 2675.5
- Liquid = 419.10
difference: 2675.5 - 419.1 = 2256.4 kJ/kg
