What is Latent heat: Definition and 206 Discussions

Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition.
Latent heat can be understood as energy in hidden form which is supplied or extracted to change the state of a substance without changing its temperature. Examples are latent heat of fusion and latent heat of vaporization involved in phase changes, i.e. a substance condensing or vaporizing at a specified temperature and pressure.The term was introduced around 1762 by British chemist Joseph Black. It is derived from the Latin latere (to lie hidden). Black used the term in the context of calorimetry where a heat transfer caused a volume change in a body while its temperature was constant.
In contrast to latent heat, sensible heat is energy transferred as heat, with a resultant temperature change in a body.

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  1. R

    Problem about a block of ice melting (specific latent heat)

    Energy lost by water = Energy gained by ice Energy lost by water = 0.16 x 4200 x (100-t) Energy gained by ice = 0.205 x L + 0.205 x (t) (where t is the temperature at thermal equilibrium). However, there does not appear to be enough info to continue. The solution, however, considered t to be...
  2. Galois_

    Thermodynamics - Latent Heat Problem (finding mass)

    Can someone walk me through this? Our teacher didn't bother to meet us synchronously ever since and I'm kinda stumped on solving this. The equation I used for this problem is: mi = [mw(cw)(ti-tf)]/[Lfi + (Tf - Ti)] mi = [190(1)(23-3)]/[79.6+(3+20)] = 37.04g mi = mass of ice mw = mass of...
  3. yecko

    Vaporization latent heat vs boiling point

    answer is 78oCdelta G = delta H - T delta S -235,310- (-277,690) = -38.56e3- T (282.59-160.70) T = -664K I am not sure if my concept is correct. May anyone help a little bit on that please? thank you
  4. M

    Specific latent heat of fusion of ice question

    a) Ew = EL + Ei mwc(T2-T1) = miL + mic(T2-0) 160 x 4.2 x (30 - 20) = 20L + (20 x 4.2 x 20) L = (6720 - 1680)/20 = 252 J/g b) accounting for 3 gram of melted ice 160 x 4.2 x (30 - 20) = (20 - 3) + (20 x 4.2 x 20)...
  5. N

    Thermodynamics: phase change and latent heat problem

    The second question is where I'm lost. The answer to the first question is 5.39 grams. The second is 10.3 grams. Until I saw the answer I was setting the equation up as if some of the original steam had condensed. But it appears that some of the original water changed into steam. Is it necessary...
  6. gaurav_samanta

    Is latent heat only released and absorbed as radiation?

    Can water simply absord the kinetic energy from colliding air molucules to change its phase? And can water transformed into ice simply have the kinetic energy of its molecules increased to balance out the lost latent heat? Would not this again change ice into water?
  7. I

    Question about thermal physics -- Ice cubes melting in water

    First, I calculated the heat required for the ice to melt: Q=mLf Q=0.150×330 Q=49.5 J Then, I calculated the final temperature of the water by forming the following equation: Q=mcΔT −49.5=(0.15+0.35)×4200×(Tf −80) Tf=80.0 degrees Celcius But the answer says 32 degrees Celsius.
  8. B

    Finding latent heat of vaporisation

    Can anyone please help me on how to tackle this question? I really do not have any clue to make a start on it? Thanks for any help!
  9. Baibhab Bose

    Phase transition between two phases with different Cv

    I actually can't figure out what kind of phase transition it is and how to proceed through..!
  10. IshaanM8

    Question about Phase Change & Latent Heat

    Homework Statement When running, some (heat) energy is lost by the evaporation of sweat. If a runner loses 1.0 MJ( Mega Joules) of energy via sweating, calculate an approximate mass of sweat evaporated from the runner. Homework Equations Q = McΔT Q (Joules) = M (Mass) c (Maximum Heat...
  11. A

    Higher and Lower heat value of combustion of Coal?

    hello my friends , i have two question about calorific value of coal why Lower heating value decrease with increase oxygen content but increase with increasing hydrogen , sulfur and carbon content ? Do this elements influence the higher heating value or not ?
  12. K

    Latent Heat: An Alternative Explanation

    1. In studies of the heat budget of the global free atmosphere, the concept of “latent heat” (now known as “enthalpy of condensation”) plays an important role[1]. 2. Both observation and experiment confirm that when humid air condenses the temperature of the remaining air increases[2]. 3. This...
  13. W

    Understanding the Derivation of the Latent Heat and Entropy Equation

    Homework Statement I came across this equation ##L / T = \Delta S## and am not too sure about its derivation. From what I know, ##L = Q/m## and ##Q = TdS ##. Substitution gives me ##\Delta S = mL / T## which isn't correct. Could someone assist me in understanding the derivation? Thanks...
  14. C

    Thermal physics -- Latent heat melting ice

    Homework Statement Question (b) (iii) Homework EquationsThe Attempt at a Solution The energy required to melt the ice is Q1=mL=3*0.025*3.3*10^5=24750J The energy released by water is Q2=mcT=0.33*4200*(22-T) Shall I calculate the energy that the ice needs after it melts into water? i.e...
  15. I

    Deriving the vapor pressure latent heat dependence

    Homework Statement There is a picture attached showing the entire problem. Equation 2.78 is the Clausius Clapeyron equation. Homework Equations Clausius Clayperon equation. L = L'T (since there is a linear dependence on temperature) The Attempt at a Solution $$ \frac{de_s}{dT} =...
  16. patrickmoloney

    Molar latent heat of phosphine

    Homework Statement [/B] Phospine exist in three forms. known as the \alpha, \beta and \gamma forms. The \alpha and \beta forms are in equilibrium with each other at 49.43 \, K, and the \alpha and \gamma forms are in equilibrium at 30.29 \, K. Obtain the molar heat of transformation for the...
  17. A

    What is the net advection of sensible and latent heat?

    I am looking at an Energy Balance equation (see images) for latent and sensible heat. However, I don't understand the terms 'advection of latent heat' Alat and 'advection of sensible heat' Ah. They positively enter the system, but how do they differ from latent and sensible heat itself?
  18. H

    Heat of Evaporation: Melting Ice to Boil Nitrogen

    Homework Statement A 0.035 kg ice cube at its melting point is dropped into an insulated container of liquid nitrogen. How much nitrogen evaporates if it is at its boiling point of -196 C? Nitrogen has heat of vaporization of 200000 J/kg Ice's specific heat is 2100 J/kg*C Homework Equations...
  19. S

    Why we use enthelpy when we calculate latent heat?

    Why we use enthalpy(h) instead of internal energy(u) when we consider latent heat?
  20. P

    Method for determining the latent heat of oils

    Just a basic question. It's as the title says, If I'd want to determine the latent of oils (or any material for that matter), is the same methodology used for determining the L.H. of ice applicable? (e.g...
  21. A

    The latent heat of crystallisation of sodium chlorate

    I am a retired electronic engineer and no scientist. I am considering the use of a saturated solution of sodium chlorate as a thermal store. My problems are: 1/ I have no idea of the quantities involved in terms of heat/gram of crystals. My intention is to maintain a supply of hot water for a...
  22. T

    Work done by a Carnot Engine. Melting ice

    Homework Statement The problem is that a Carnot contains Boiling water in the hot reservoir and ice water in the cold reservoir. Given that 0.0400kg of ice is melted in 5 minutes, what is the amount of work done by the engine. Homework Equations Qh/Qc=Th/Tc W=Qh-Qc W=(1-Tc/Th)Qs q=mHf...
  23. heartshapedbox

    Latent heat and specific heat in insulated container

    Homework Statement A 1.0kg of ice at 0◦C, 3.0kg of water at 0◦C, and 5.0kg of iron at temperature T are placed in a sealed and insulated container. cFe =400J/ kg◦C ,cWater=4200J/ kg◦C , cIce= 2000 J/ kg◦C latent heat for ice is 3.3×105 J . The equilibrium temperature is 20◦C.Homework...
  24. MattNguyen

    Thermodynamics adding ice to water problem with latent heat

    Homework Statement Initially you have mW = 4.6 kg of water at TW = 74°C in an insulated container. You add ice at TI = -19°C to the container and the mix reaches a final, equilibrium temperature of Tf = 33°C. The specific heats of ice and water are cI = 2.10×103 J/(kg⋅°C) and cW = 4.19×103...
  25. Ashleykins

    How to Calculate Potential Energy and Latent Heat in Physics?

    I have two homework questions that I am desperate for some help on. I've posted them on our class discussion page, and I'm on my last attempt. We get three attempts on our homework. The first question deals with SPE and the second deals with latent heat. For Question 1: 1. Homework Statement...
  26. S

    Heat Capacity and Latent Heat question

    Homework Statement A 75.0g ice cube at 0 C is placed in 825g of water at 25 C. Find final temp. Homework Equations Well none really, this should be simple plugging into to heat equations. The Attempt at a Solution Heat required to melt ice = (0.075kg)(3.33*10^5) = 24975 J Heat required to...
  27. J

    How Does the Heat Transfer Rate Affect a Beaker of Liquid Nitrogen?

    Homework Statement The mass of liquid nitrogen in an open beaker is found to have decreased by 46.3 g in 10 minutes. If the s.l.h of vaporisation of nitrogen at its boiling point is 1.99 x 105, at what rate were the surroundings heating the beaker? Why is the heat capacity of the beaker...
  28. Tafe

    Quantity of heat, phase change of ice to water

    Homework Statement A 1x106 kg piece of ice is placed into a lake. How much heat is taken from the lake to raise the temperature of the ice from 0 °C to 1x10-20 °C? How much volume does the lake increase by? Latent heat for water is 334x103 J/kg Homework Equations Found in my textbook, cice =...
  29. E

    What other forms of energy does latent heat convert to during a phase change?

    The kinetic theory says that temperature is the measure of the average kinetic energy. That would mean then : The temperature rises with the rise in kinetic energy. We know that when matter changes state 'latent heat' helps in 'breaking the bonds' at the transition phase and that this 'extra...
  30. J

    Why specific latent heat of vaporisation > fusion?

    1. Homework Statement Homework Equations First law of thermodynamics, ΔU=q+W The Attempt at a Solution Ok so, I know that when liquid evaporates, the change in volume is much greater than that when solid melts. And for both cases, distance of separation of atoms increases too, so PE...
  31. M

    How many kg of ice must be dropped to make Tf= 22.7C?

    Homework Statement An insulated beaker with neglible mass contains .3kg of water at a temp of 78.6 C. How many kg of ice at -19.6 C must be dropped into the water to make Tf= 22.7C? Specific heat for water= 4190 J/kgK specific heat for ice= 2100 J/kgK heat of fusion for water= 334kJ/kg...
  32. A

    What is the latent heat for medium carbon steel

    I'have searched a lot but could not find latent heat for any kind of medium carbon steel for latent heat from solid to liquid and from liquid to gas. Also I want to know the corresponding melting point and boiling point for that know of steel. Any link for a table would be greatly appreciated...
  33. Kara386

    Calculate the latent heat of fusion of ice

    Homework Statement I'm given that for water near 0 degrees, dp/dT = ##-1.4\times 10^7PaK^-1##. And that water has a specific volume of ##1\times 10^{-3}m^3kg^{-1}##, while for ice the specific volume is ##1.09\times 10^{-3}m^3kg^{-1}##. Calculate the latent heat of fusion L for ice, and...
  34. H

    Specific latent heat of fusion

    Homework Statement The graph below shows the result of an investigation in which an initially solid specimen of nitrogen absorbs heat a constant rate. Nitrogen melts at 63 K and the specific heat capacity of solid nitrogen is 1.6 kJ kg^-1 K^-1. Homework Equations shc od solid nitrogen = 1.6...
  35. G

    Latent Heat of Phase Transition: Origin & Explanation

    Hello, We often hear about latent heat of vaporisation for a liquid, which basically corresponds to the energy required to break the hydrogen inter-molecular bonds in the liquid phase to form the gas. I was wondering, what is the equivalent physical explanation for the latent heat of a...
  36. C

    Lower and Higher Heating Values of Coal: Why do they exist?

    Hello friends, The balanced chemical equation for the combustion of carbon is: C(solid) + O2(gas) -> CO2(gas) Now, the lower and higher heating value of hydrocarbon fuels (such as methane) exists because in the LOWER heating value, you are subtracting away the latent heat of vaporization of...
  37. N

    Thermodynamics question thanks so much for the help

    Homework Statement a small lump of ice at 0 degrees celsius falls to the Earth's surface. when the hailstone hist the surface, all of the kinetic energy of the hailsotne is transferred to thermal energy in the ice. calculate the minimum speed of the hailstone so that it just melts when it hits...
  38. T

    Ice in water question - what is final temperature?

    Homework Statement An ice cube melts in a 10oC glass of water (mass of water is 225g). If the ice is allowed to melt completely, what will the final temperature of the water be? (we're told that the mass of ice can be ignored) Ti = 10oC Latent heat of fusion = Lf = 334000 J/kg specific heat...
  39. D

    Does electrical conduction require energy state changes?

    Molecules do not use magnetic energy as latent heat - adding magnetic energy does not cause a phase change. If electrical conduction indeed required energy state changes, then during electrical conduction, a change of energy state would likely consume magnetic energy as latent heat, instead of...
  40. Mnemonic

    Thermodynamics relating to temperature and phase changes

    Homework Statement Suppose a room with 75 m3 of air also contains 80 kg of glycerol and the initial temperature in the morning is 16 °C. If 1.2 kWh of heat is added to the room between morning and afternoon, calculate the final temperature of the air in the room in the afternoon. Use 18 °C for...
  41. L

    Supercooled water - latent heat of fusion

    During water solidification at 1 atm, about 80 cal/g of heat are released; since ice specific heat is less than 1 cal/(g °C) it means that if this heat would be totally transferred to the ice, its temperature should increase of more than 80°C. How then it is that very fast solidification from...
  42. C

    Latent Heat Q: 50g Ice Melting in 1kW Oven

    Homework Statement 50g of ice is placed in a 1kW microwave oven and the oven is turned to full power. Estimate the time it will take for the ice to melt. The specific latent heat capacity of ice in 330kJ −1 kg . Is your answer likely to be an overestimate or an underestimate? Explain your...
  43. It's me

    Estimate the latent heat of water

    Homework Statement Try to estimate the latent heat of vaporization of water and nitrogen using the Van der Waals model. What happens? Homework Equations $$ΔQ=TΔS=L$$ $$S=nR[\ln(\frac{(V−nb)T^{3/2}}{nΦ})+\frac{5}{2}]$$The Attempt at a Solution I predict the latent heat of vaporization of...
  44. It's me

    Estimate the latent heat of water with Van der Waals

    Homework Statement Try to estimate the latent heat of vaporization of water and nitrogen using the Van der Waals model. What happens? Homework Equations $$\Delta Q = T\Delta S=L$$ $$S=nR\left[ \ln\left(\frac{(V-nb)T^{3/2}}{n\Phi}\right)+\frac{5}{2} \right]$$ The Attempt at a Solution I...
  45. Z

    What is the latent heat of the water evaoparation

    since water can turn into steam at any temperature, what is the latent heat of water evaporation. I know the late heat value at the boiling point. but what is the latent heat at 20 Celsius
  46. S

    Latent heat of fusion for water question

    Hello, I am doing some research involving supercooled water flash freezing into ice. I am doing some calculations and I think that I must be wrong judging by my result. Using the latent heat of fusion of water, and the specific heat of water, I can calculate a temperature value which should...
  47. T

    Latent Heat in Solid-->Liquid transitions (phase change)

    Homework Statement Show that in Solid to Liquid transitions at T \ll {T}_{c} , L\simeq constant where {T}_{c}, L are the critic temperature and latent heat respectively. Homework Equations \left( \frac{d ( \frac {L} {T})} {dT} \right) = \frac {{c}_{p2}-{c}_{p1}} {T}+ \frac...
  48. A

    Modeling of moist-adiabatic temperature?

    Hi, I need to find some good article or book related to the modeling of this process: the parcel of air goes up from the surface to the top of troposphere ( to 12000 m ), we know the conditions at the bottom such as temperature, pressure and humidity, we assume that the parcel is isolated...
  49. T

    Latent Heat Solid->gas Liquid->gas transitions

    Homework Statement Show that in Solid to gas and Liquid to gas transitions at T \ll {T}_{c} , L\simeq a+bT where {T}_{c}, L are the critic temperature and latent heat respectively and a,b constants.Homework Equations \left( \frac{d ( \frac {L} {T})} {dT} \right) = \frac...