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enthalpy of fusion wikipedia jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 overview 2 examples 3 solubility prediction toggle solubility prediction subsection 3 1 proof 4 see also 5 notes 6 references toggle the table of contents enthalpy of fusion 56 languages afrikaans aragonés العربية asturianu български বাংলা bosanski català čeština чӑвашла dansk deutsch español eesti euskara فارسی suomi français galego hrvatski magyar հայերեն interlingua bahasa indonesia italiano 日本語 la lojban ქართული қазақша 한국어 lietuvių മലയാളം bahasa melayu nederlands norsk nynorsk norsk bokmål occitan polski português română русский srpskohrvatski српскохрватски සිංහල simple english slovenčina slovenščina српски srpski svenska తెలుగు тоҷикӣ ไทย українська اردو oʻzbekcha ўзбекча tiếng việt 中文 edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikimedia commons wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia enthalpy change when a substance melts enthalpies of melting and boiling for pure elements versus temperatures of transition demonstrating trouton s rule in thermodynamics the enthalpy of fusion also known as latent heat of fusion or heat of fusion of a substance is the change in its enthalpy resulting from providing energy typically heat to a specific quantity of the substance to change its state from a solid to a liquid at constant pressure the enthalpy of fusion is the amount of energy required to convert one mole of solid into liquid for example when melting 1 kg of ice at 0 c under a wide range of pressures 333 55 kj of energy is absorbed with no temperature change the heat of solidification when a substance changes from liquid to solid is equal in magnitude and opposite in sign this energy includes the contribution required to make room for any associated change in volume by displacing its environment against ambient pressure the temperature at which the phase transition occurs is the melting point or the freezing point according to context by convention the pressure is assumed to be 1 atm 101 325 kpa unless otherwise specified overview edit the enthalpy of fusion is a latent heat because while melting the heat energy needed to change the substance from solid to liquid does not cause any increase in temperature temperature remains constant during the freezing or melting process and only begins to change again assuming the energy input or removal cooling continues after the phase change is complete the latent heat of fusion is the enthalpy change of any amount of substance when it melts when the heat of fusion is referenced to a unit of mass it is usually called the specific heat of fusion while the molar heat of fusion refers to the enthalpy change per amount of substance in moles the liquid phase has a higher internal energy than the solid phase this means energy must be supplied to a solid in order to melt it and energy is released from a liquid when it freezes because the molecules in the liquid experience weaker intermolecular forces and so have a higher potential energy a kind of bond dissociation energy for intermolecular forces when liquid water is cooled its temperature falls steadily until it drops just below the line of freezing point at 0 c the temperature then remains constant at the freezing point while the water crystallizes once the water is completely frozen its temperature resumes a colder trend the enthalpy of fusion is almost always a positive quantity helium is the only known exception 1 helium 3 has a negative enthalpy of fusion at temperatures below 0 3 k helium 4 also has a very slightly negative enthalpy of fusion below 0 77 k 272 380 c this means that at appropriate constant pressures these substances freeze with the addition of heat 2 in the case of 4 he this pressure range is between 24 992 and 25 00 atm 2 533 kpa 3 standard enthalpy change of fusion of period three standard enthalpy change of fusion of period two of the periodic table of elements substance heat of fusion melting temperature c cal g j g water 79 72 333 55 0 0 methane 13 96 58 99 182 46 propane 19 11 79 96 187 7 glycerol 47 95 200 62 17 8 formic acid 66 05 276 35 8 4 acetic acid 45 90 192 09 16 17 acetone 23 42 97 99 94 9 benzene 30 45 127 40 5 53 myristic acid 47 49 198 70 54 4 palmitic acid 39 18 163 93 62 9 sodium acetate h2o 63 69 264 289 4 58 trihydrate sodium sulfate h2o 61 254 5 32 38 decahydrate stearic acid 47 54 198 91 69 3 gallium 19 2 80 4 29 76 paraffin wax c 25 h 52 47 8 52 6 200 220 46 68 these values are mostly from the crc handbook of chemistry and physics 62nd edition the conversion between cal g and j g in the above table uses the thermochemical calorie cal th 4 184 joules rather than the international steam table calorie cal int 4 1868 joules examples edit to heat 1 kg of liquid water from 0 c to 20 c requires 83 6 kj see below however heating 1 kg of ice from 0 c to 20 c requires additional energy to melt the ice we can treat these two processes independently and using the specific heat capacity of water to be 4 18 j g k thus to heat 1 kg of ice from 273 15 k to water at 293 15 k 0 c to 20 c requires 1 333 55 j g heat of fusion of ice 333 55 kj kg 333 55 kj for 1 kg of ice to melt plus 2 4 18 j g c 20 c 4 18 kj kg c 20 c 83 6 kj for 1 kg of water to increase in temperature by 20 c 1 2 333 55 kj 83 6 kj 417 15 kj for 1 kg of ice to increase in temperature by 20 c silicon has a heat of fusion of 50 21 kj mol 50 kw of power can supply the energy required to melt about 100 kg of silicon in one hour 50 kw 50 kj s 180 000 kj h 180 000 kj h 1 mol si 50 21 kj 28 g si mol si 1 kg si 1 000 g si 100 4 kg h solubility prediction edit the heat of fusion can also be used to predict solubility for solids in liquids provided an ideal solution is obtained the mole fraction x 2 displaystyle x_ 2 of solute at saturation is a function of the heat of fusion the melting point of the solid t fus displaystyle t_ text fus and the temperature t displaystyle t of the solution ln x 2 δ h fus r 1 t 1 t fus displaystyle ln x_ 2 frac delta h_ text fus circ r left frac 1 t frac 1 t_ text fus right here r displaystyle r is the gas constant for example the solubility of paracetamol in water at 298 k is predicted to be x 2 exp 28100 j mol 1 8 314 j k 1 mol 1 1 298 k 1 442 k 0 0248 displaystyle x_ 2 exp left frac 28100 text j mol 1 8 314 text j k 1 text mol 1 left frac 1 298 text k frac 1 442 text k right right 0 0248 since the molar mass of water and paracetamol are 18 0153 g mol 1 and 151 17 g mol 1 and the density of the solution is 1000 g l 1 an estimate of the solubility in grams per liter is 0 0248 1000 g l 1 18 0153 g mol 1 1 0 0248 151 17 g mol 1 213 4 g l 1 textstyle frac 0 0248 times frac 1000 text g l 1 18 0153 text g mol 1 1 0 0248 times 151 17 text g mol 1 213 4 text g l 1 1000 g l mol 18 0153g is an estimate of the number of moles of molecules in 1l solution using water density as a reference 0 0248 1000 g l mol 18 0153g is the molar fraction of substance in saturated solution with a unit of mol l 0 0248 1000 g l mol 18 0153g 151 17g mol is the solute s molar fraction equivalent mass conversion 1 0 0248 will be the fraction of the solution that is solvent which is a deviation from the real solubility 240 g l of 11 this error can be reduced when an additional heat capacity parameter is taken into account 6 proof edit at equilibrium the chemical potentials for the solute in the solution and pure solid are identical μ solid μ solute displaystyle mu _ text solid circ mu _ text solute circ or μ solid μ liquid r t ln x 2 displaystyle mu _ text solid circ mu _ text liquid circ rt ln x_ 2 with r displaystyle r the gas constant and t displaystyle t the temperature rearranging gives r t ln x 2 μ liquid μ solid displaystyle rt ln x_ 2 left mu _ text liquid circ mu _ text solid circ right and since δ g fus μ liquid μ solid displaystyle delta g_ text fus circ mu _ text liquid circ mu _ text solid circ the heat of fusion being the difference in chemical potential between the pure liquid and the pure solid it follows that r t ln x 2 δ g fus displaystyle rt ln x_ 2 left delta g_ text fus circ right application of the gibbs helmholtz equation δ g fus t t p δ h fus t 2 displaystyle left frac partial left frac delta g_ text fus circ t right partial t right _ p frac delta h_ text fus circ t 2 ultimately gives ln x 2 t δ h fus r t 2 displaystyle left frac partial left ln x_ 2 right partial t right frac delta h_ text fus circ rt 2 or ln x 2 δ h fus r t 2 δ t displaystyle partial ln x_ 2 frac delta h_ text fus circ rt 2 times delta t and with integration x 2 1 x 2 x 2 δ ln x 2 ln x 2 t fus t δ h fus r t 2 δ t displaystyle int _ x_ 2 1 x_ 2 x_ 2 delta ln x_ 2 ln x_ 2 int _ t_ text fus t frac delta h_ text fus circ rt 2 times delta t the result is obtained ln x 2 δ h fus r 1 t 1 t fus displaystyle ln x_ 2 frac delta h_ text fus circ r left frac 1 t frac 1 t_ text fus right see also edit enthalpy of vaporization heat capacity thermodynamic databases for pure substances joback method estimation of the heat of fusion from molecular structure latent heat lattice energy heat of dilution notes edit atkins jones 2008 p 236 ott boerio goates 2000 pp 92 93 hoffer j k gardner w r waterfield c g phillips n e april 1976 thermodynamic properties of 4 he ii the bcc phase and the p t and vt phase diagrams below 2 k journal of low temperature physics 23 1 63 102 bibcode 1976jltp 23 63h doi 10 1007 bf00117245 s2cid 120473493 page 155 in thermal energy storage methods thermal energy storage 2021 pp 125 260 doi 10 1002 9781119713173 ch3 isbn 978 1 119 71315 9 tao wen kong xiangfa bao anyang fan chuangang zhang yi 17 november 2020 preparation and phase change performance of graphene oxide and silica composite na 2 so 4 10 h 2 o phase change materials pcms as thermal energy storage materials materials 13 22 5186 doi 10 3390 ma13225186 pmc 7698442 pmid 33212870 hojjati h rohani s november 2006 measurement and prediction of solubility of paracetamol in water isopropanol solution part 2 prediction organic process research development 10 6 1110 1118 doi 10 1021 op060074g references edit atkins peter jones loretta 2008 chemical principles the quest for insight 4th ed w h freeman and company p 236 isbn 978 0 7167 7355 9 ott bj bevan boerio goates juliana 2000 chemical thermodynamics advanced applications academic press isbn 0 12 530985 6 v t e states of matter list timeline state solid liquid gas vapor supercritical fluid plasma low energy bose einstein condensate fermionic condensate degenerate matter quantum hall rydberg matter strange matter superfluid supersolid photonic molecule high energy qcd matter quark gluon plasma color glass condensate other states colloid crystal liquid crystal time crystal quantum spin liquid exotic matter programmable matter dark matter antimatter magnetically ordered antiferromagnet ferrimagnet ferromagnet string net liquid superglass phase transitions boiling boiling point condensation critical line critical point crystallization deposition evaporation flash evaporation freezing chemical ionization ionization lambda point melting melting point recombination regelation saturated fluid sublimation supercooling triple point vaporization vitrification quantities enthalpy of fusion enthalpy of sublimation enthalpy of vaporization latent heat latent internal energy trouton s rule volatility concepts baryonic matter binodal compressed fluid cooling curve equation of state leidenfrost effect macroscopic quantum phenomena mpemba effect order and disorder physics spinodal superconductivity superheated vapor superheating thermo dielectric effect authority control databases international gnd fast national united states france bnf data israel retrieved from https en wikipedia org w index php title enthalpy_of_fusion oldid 1365422058 category enthalpy hidden categories articles with short description short description is different from wikidata this page was last edited on 22 july 2026 at 08 51 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal 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