Talk:Enthalpy of fusion

Calculations not right
1 calorie = 4.184 J.

1 calorie/gram = 4.184 kJ/kg

Something is badly wrong with the table in the article.

David B. Benson (talk) 23:51, 30 March 2008 (UTC)

How to quantify enthalpy of fusion at the atomic level?
There is a fundamental problem with the presentation of this page. The Enthalpy of fusion is the amount of energy that must be REMOVED from a substance for it to transition (fuse) from a liquid to a solid. It must have a negative value, as energy must be removed to achieve the fusion. The enthalpy of melting for the same substance is the exact same number, but is the positive number, as you need to add heat to transition from solid to liquid

I was trying to explain adding salt to ice, which causes the resulting water (assuming the ice is not so cold as to stay solid) to be colder than the original ice, in terms of energy transfer.

According to the formula that average kinetic energy ∝ T, the heat going into melting the ice doesn't increase the atoms' kinetic energy. Therefore, it seems the heat of fusion energy just increases potential energy w.r.t overcoming attractive forces. However, it seems strange that KE would stop increasing while potential energy continues to increase, instead of them increasing together continuously (think of a spring with a bouncing ball attached).

Can somebody correct my conjecture? --UncleJoe1985 (talk) 08:54, 20 June 2009 (UTC)

no place for explaining differences with calories on food
Somebody added an explanatory note in the first paragraph explaining the differences with food calories. I don't think this is the place to discuss something so unrelated to the thema. Also, if nobody oposses, I'll proceed to deletion / move to calorie page in two weeks.

Angelpeream (talk) 14:32, 19 January 2010 (UTC)

Regarding the image
The image bothers me for numerous reasons of unprofessionalism, but most strikingly is the label of the horizontal axis that says "deg K." Units Kelvin are not measured in degrees. 75.169.224.79 (talk) 04:20, 20 January 2010 (UTC)

Conceptual difficulties
The text says:

When thermal energy is withdrawn from a liquid or solid, the temperature falls. ... However, at the transition point between solid and liquid (the melting point), extra energy is required (the heat of fusion). For freezing, the molecules of a substance arrange in an ordered state. For them to maintain the order of a solid, extra heat must be withdrawn. ... The temperature stops falling at (or just below) the freezing point, because energy from heat is stored in the form of primarily potential energy to build the solid lattice, rather than to increase the net kinetic energy (thermal energy) of the molecules. This introduced heat that does not result in a temperature change, is called a latent heat. The temperature of the system does not fall further until the liquid has frozen completely.

''[OK, let me see if I’ve got this straight. The temperature of a liquid or solid falls because thermal energy is withdrawn.] The temperature stops falling at (or just below) the freezing point, because energy from heat is stored in the form of primarily potential energy to build the solid lattice,… [No problem so far.]''

rather than to increase the net kinetic energy (thermal energy) of the molecules. ''[Wait! Thermal energy is being withdrawn. This withdrawal *increases* the net kinetic energy (thermal energy) of the molecules? Should this phrase be deleted?]''

This introduced heat that does not result in a temperature change, is called a latent heat. ''[Wait! Thermal energy is being withdrawn. Why do we call this “introduced” heat? Shouldn’t we call this “retained” heat or “stored” heat—at least for the process of freezing?]'' ThatAMan (talk) 19:54, 28 February 2011 (UTC) — Preceding unsigned comment added by ThatAMan (talk • contribs) 21:57, 27 February 2011 (UTC)

Definition and explanation
I see two problems with this article as it stands. In the first para, there is confusion about the definition. The latent heat of fusion is the enthalpy change in a body when it melts. The specific heat of fusion is the enthalpy change per unit mass, and the molar heat of fusion is the enthalpy change per mole. This could be made much clearer.

In the third para, I agree with ThatAMan that the explanation is poorly worded and even misleading. The fundamental point here is that the liquid phase has a higher internal energy than the solid phase. This means energy must be supplied to a solid body in order to melt it and energy will be released from a liquid when it freezes. I propose replacing the third para with this:

When a body passes from a solid phase to a liquid phase, its molecules experience weaker intermolecular forces. Consequently the liquid phase contains a higher potential energy. This means that energy must be supplied to a solid body in order to melt it and energy will be released from a liquid when it freezes. In addition to the change in potential energy, there may also be a much smaller change in enthalpy caused by the fact the liquid and solid phases have different densities, so that some work has to be performed to change the phase.

This is still fairly thin as a thermodynamic explanation, but at least it is not misleading.

If no objections, I'll update in two weeks. — Preceding unsigned comment added by Dezaxa (talk • contribs) 18:24, 19 September 2011 (UTC)

Please reformat the tables to per mol
This is standard practice and is far more useful. elle vécut heureuse à jamais  (be free) 21:46, 30 September 2011 (UTC)

Kinetic and potential energy
I have changed the reference to kinetic energy to potential energy. Molecules of liquids and solids at the melting point have the same kinetic energy, because they are at the same temperature. The difference in internal energy is one of potential energy, because of the weaker bonds in the liquid phase. Dezaxa (talk) 02:17, 12 October 2011 (UTC)
 * Wouldn't their heat capacities be different? elle vécut heureuse  à jamais  (be free) 00:18, 14 October 2011 (UTC)

Applications
It took me 12 minutes to figure out what portion of ice would cool x units of room temperature water to freezing, surely one of the main reasons to look for the heat of fusion, so I added it. Calculation: 333.55 kJ to melt ice ~= (4 * 83.6 kJ) for 4kg of water down to 0 °C degrees from 20 °C MusicScienceGuy (talk) 20:39, 10 February 2012 (UTC)

Conflict and redundancies
¿Why are there separate articles for Enthalpy of fusion (and Enthalpy of vaporization) and Latent heat, when they describe essentially the same concept? To make matters worse, the data in the tables are different (108 kJ/kg for ethanol in the article on "Latent Heat" and 109 kJ/kg in the article about enthalpy). --Gonfer00 (talk) 09:10, 25 February 2012 (UTC)

This is because Latent heat is a more general concept that the enthalpy of fusion: the enthalpy of fusion only deals with the liquid/solid transition.Mgibby5 (talk) 18:31, 22 February 2015 (UTC)

Enthalpy of fusion of water salt mixture?
I have scoured the internet searching for any info on the enthalpy of fusion of water-salt ice, but havent been able to find anything. perhaps one of you knowledgable folks can direct me to where I can find this? or post it if you think its relevant? Dazalc (talk) 00:53, 16 June 2012 (UTC)

edit: found a source that covers 0 to -8 C on 0 to 12% salinity:NOT Dazalc (talk) 23:59, 16 June 2012 (UTC)

Kinetic and potential energy (again)
I've again changed back the reference from kinetic energy to potential energy. Molecules of water and ice at the same temperature have the same kinetic energy - this follows from the kinetic theory of heat, as long as we are not talking about very low temperatures where quantum effects are signigicant. Molecules of liquid water have a higher potential energy, because energy is needed to break the intermolecular bonds that are present in the solid phase. This is similar to a bond dissociation energy, but for intermolecular forces. It is a misconception to suppose that because bonds are stronger in the solid phase that this means the potential energy is higher; the opposite is true: bonds represent a reduction in free energy in comparison to free particles. Dezaxa (talk) 18:46, 28 October 2013 (UTC)

Origin of the name?
The name fusion in this context is often confusing to high school science students and others without a lot of experience in the field. To them, fusion talks about bringing things together, like hydrogen nuclei, but here fusion is referring to melting, which actually means that the individual molecules are moving apart, from a rigid structure to a flowing form. What is the origin of the name fusion in this context? In fact there is somebody earlier in this talk page that was similarly confused. Nutster (talk) 14:27, 6 April 2015 (UTC)

hmmm something is Missing
The article does not say what atomic property(s) MOST effect heat of fusion. This is a solved mystery and should not be left a mystery to the reader. please show a graph against some property versus heat of fusion — Preceding unsigned comment added by 72.219.204.96 (talk) 17:50, 1 November 2015 (UTC)

Gallium
Gallium has a melting point of about room temperature, 85.5763 °F. Due the the rather large Enthalpy of fusion, it can exist as a solid or a liquid at approximately room temperature. Easy to acquire, inexpensive and non-toxic it is a good material (element, metal) to use for demonstrating Enthalpy of fusion.

DGerman (talk) 21:00, 11 July 2017 (UTC)

Enthalpy of melting
I think that this variant of name is preferable to using the word fusion!--5.2.200.163 (talk) 17:12, 28 November 2017 (UTC)

There needs to be an explanation of the name
I came to this page to learn why melting is referred to as fusion. I assume that there is a good reason, but frankly, the term is incredibly stupid without an actual explanation, and there needs to be one on the page. — Preceding unsigned comment added by 128.227.122.81 (talk) 01:59, 4 December 2017 (UTC)
 * It seems that the term fusion is actualul used for freezing or solidification, based on how the word fusion is used in the expression heat fusion which implies welding - puting together two pieces of solid which are joined or fused together.--109.166.131.41 (talk) 00:26, 16 July 2019 (UTC)


 * I'm not quite convinced by that explanation...I don't necessarily think you're wrong - that may be correct, for all I know. It seems a bit of a logical leap to me, though, too refer too all melting as fusion because joining two solids can involve the partial melting of them Firejuggler86 (talk) 11:05, 29 January 2021 (UTC)

Amount of heat absorbed by melting ice not correct.
This article says "When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C." (80C = 176F). There is no reference for this assertion. However, in Enthalpy of fusion - Wikipedia, we see that the enthalpy of fusion for water is 79.72 cal/g. This converts to 143 BTU / lb of ice. A BTU is the amount of heat energy needed to raise 1 pound of water 1 degree Fahrenheit. So the correct statement would be "When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 61.0 °C." Using the corrected value explains why we call1 ton of HVAC heating or cooling = 12,000 BTUHs (BTU hours). Historically, when ice was made and shipped in bulk, 288,000 BTUs were (and are) needed to freeze 1 ton (2,000 pounds) of water in one day. Converted to an hourly rate, that 12,000 BTUs per hour, or 1 ton BTUH. Claudemundy (talk) 14:34, 27 February 2024 (UTC)


 * Correction, "When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 61.9 °C." Claudemundy (talk) 14:36, 27 February 2024 (UTC)

The number in the article appears to me to be correct. I'm not sure where you are getting 61.9 from. 79.72 cal/g converts to 143 btu/lb as you say, but when you divide this by 1.8 to convert between the scales for Fahrenheit and Celcius, this just takes you back to 79.7 degrees Celcius. Dezaxa (talk) 20:31, 27 February 2024 (UTC)