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. P

    Latent Heat Problem? Not sure how to solve

    Homework Statement A window of a car is found to be covered with 0.8cm of ice. If the area of the window is 1 m2, and the ice is at -12 degrees Celsius, what is the minimum heat required to melt all the ice? Take the density of ice to be 900 kg/m3, the specific heat capacity of ice to be 0.5...
  2. J

    Latent Heat of Fusion & Internal Energy

    I understand the main concepts around this topic but I am struggling to find any information about the potential energy involved in the latent heat of fusion. My book defines internal energy as kinetic and potential unlike an ideal gas that is assumed to have just kinetic energy. When a...
  3. M

    How do I find the specific latent heat of fusion of nitrogen?

    When doing an experiment to find the specific latent heat of fusion of liquid nitrogen, you find that 100 kJ of heat must be removed to freeze 3.8kg of nitrogen at its freezing point. What value will you get for the specific latent heat of fusion of nitrogen? Power=100kj M=3.8kg I don't...
  4. G

    How to estimate latent heat of polymorphic phase transitions

    Hello, I know that the latent heat of a first-order isothermal and isobaric phase transition is in general given by the difference in enthalpies between the two phases, but my question is: do you know if there is there a way to estimate its value "from first principles" for the case of a...
  5. S

    Latent Heat of Fusion and Ice Maker Problem

    Homework Statement You are required to calculate the efficiency of an ice-making machine that takes in water at a temperature of 16°C and produces ice cubes at a temperature of -6°C. Water is taken in at the rate of 1kg every 5 minutes and the input power to the machine is 300W. The Specific...
  6. R

    Thermal Conductivity and latent heat

    Homework Statement If a copper kettle has a base of thickness 2.0mm and an area 3.0 x 10-2 m2 estimate the steady difference in temperature between the inner and outer surface of the base which must be maintained to enable enough heat too pass through so that the temperature of 1 kg of...
  7. B

    Latent Heat Question: Calculate Vaporization Rate & Energy Needed

    Homework Statement A scientist heats up a substance by applying heat at a constant rate of 75 J/s. She measures that it takes 1 minute for 100 grams of the substance to evaporate. What is the latent of vaporization of this substance? If she starts with 1 kg of the substance, how long...
  8. E

    How do additives in ice change Latent Heat of Fusion?

    When using ice to keep a room (or in my case, a cooler) cold, one would want it to have a high specific heat capacity and a high latent heat of fusion, so that it would absorb a lot of energy as it melts. Basically, so that it melts as slowly as possible. I know that adding salt to road ice...
  9. V

    Length of cooling including latent heat

    Hello, I would like to know how to calculate how long the phase transition when cooling lasts. So basically how long the latent transition lasts. I really don't have any ideas how this could be calculated, although I would assume it is function of the mass. Any help is much appreciated.
  10. KiNGGeexD

    What is the role of ε in understanding latent heat?

    This is a question of understanding notes today:) I'm struggling to follow these notes, they are not very well written and a tad sporadic! I was just reading through them and I'm not quite sure what the term ε actually is in this case? I am assuming it is a constant although on the first page...
  11. F

    Does this equation exist? (Latent heat, temperature, entropy)

    Evening all. I've seen this equation written down but can not for the life of me find it on tinterweb, is it correct? L = Tconst(S2-S1)
  12. P

    Latent heat of Fusion and transfer problem

    Homework Statement A 100g (.1kg) cube o ice at 0dC (d=degrees) is placed in 1kg of water that was originally at 80dC. What is the nal temperature of the water after the ice has melted? Answer: 65.5dCHomework Equations Lf = Q/m Q=(DelT)mCThe Attempt at a Solution At first I looked up the latent...
  13. F

    Thermal physics - entropy change (latent heat, specific heat etc)

    Hi all, could somebody have a look over my answers for this question please? The value I got for the second part seems quite feeble. Homework Statement The Attempt at a Solution Part a) Key m = mass cs = specific heat bronze cm = specific heat molten bronze Tfus = melting...
  14. B

    How Does Latent Heat Affect Sweat Evaporation in Cooling the Body?

    The latent heat of vapourisation of H2O at body temperature (37°C) is 2.42x106 J Kg-1. To cool the body of a 75 Kg jogger (average specific heat capacity = 3500 J Kg-1C°-1) by 1.5 °C, how many Kilograms of water in the form of sweat have to be evaporated? Q = mcΔT I'm confused about what to do...
  15. C

    Latent heat in water vapor below boiling

    Hi - I'm a physics newbie so this is an elementary question, but I can't find the answer with a google search. Water evaporates at a wide range of temperatures, what is the latent heat in the water vapor (in calories or Joules), for example, at 30°C, 60°C? Assume standard atmospheric...
  16. STEMucator

    Yes, your approach and calculations look correct. Good job!

    Homework Statement How much heat is required to heat 0.2kg of ice from -20°C to 30°C? Homework Equations Total heat lost or gained : ##Q = mcΔt## where ##Δt## is the change in temperature and c is the heat capacity. Latent Heat Fusion : ##Q = mL_f## The Attempt at a Solution From my...
  17. Saitama

    Finding latent heat of vaporisation as a function of temperature

    Homework Statement The vapour pressure of a certain liquid is given by the equation: \log_{10}P=3.54595-\frac{313.7}{T}+1.40655\log_{10}T where ##P## is the vapour pressure in mm and T is temperature in kelvin. Determine the molar latent heat of vapourisation as a function of temperature...
  18. R

    Calculating Heat Energy Changes in a Water and Ice System

    Homework Statement mass of cup 1.78g initial mass of water and cup - 54.26g finlal mass of water after ice added - 91.26g initial temperature - 27°C temperature after heated - 92°C temperature after ice added - 35°C problem 1) how much heat energy did the original mass of water lose...
  19. fluidistic

    How to Calculate Latent Heat at a New Point on the Coexistence Curve?

    Homework Statement I'm stuck in the following problem: In a particular solid-liquid phase transition the point ##T_0##, ##P_0## lies on the coexistence curve. The latent heat of vaporization at this point is ##l_0##. A nearby point on the existence curve has pressure ##P_0+p## and temperature...
  20. J

    Latent Heat of CAS No. 4719-04-4

    I'm hoping someone can help me find information on this, I've been searching to no avail for it. I need to know the latent heat of 2, 2', 2" (Hexahydro-1,3,5-triazine-1,3,5-triyl)triethanol CAS No. 4719-04-4 at P = 480 Psig, T = 150°F. Can anyone point me in the right direction for some info...
  21. J

    What is the Difference Between Latent Heat and Specific Heat?

    Homework Statement I took a test and got it back I'm wondering if my prof. definition is correct. The heat required per unit mass of a substance to produce a phase change is called? A. specific heat B. Specific heat capacity C. latent heat I said it was C. He say's B Please...
  22. C

    What is the definition of latent heat and how does it apply to phase changes?

    I need some clarifications on the precise definitions and scope of latent heat. My textbook defines latent heat as the amount of energy absorbed or releases during a phase change process. So if I have a pot of liquid water and I vaporize it completely, then the latent heat is simply the energy I...
  23. W

    Latent Heat Transfer Rate in a Pipeline help please

    Hey guys, first post. I'm trying to determine to the rate at which liquids drop out of a gas pipeline. I've modeled the system in a chemical process program, but its only a steady state model. Anyways, here's some of what I can get out of that program: Heat of vaporization Total Heat Transfer...
  24. M

    Chemical potential in Thermodynamics to find latent heat of vaporization

    Homework Statement The latent heat of vaporization of a substance is defined as the amount of heat required to transform the substance from its liquid into its vapor phase. A certain material has a boiling point of 700K and its molecules have three degrees of freedom in the liquid phase but...
  25. R

    Latent Heat and conservation of energy

    Homework Statement A cooking vessel on a slow burner contains 11.0 kg of water and an unknown mass of ice in equilibrium at 0°C at time t = 0. The temperature of the mixture is measured at various times. During the first 50.0 min, the mixture remains at 0°C. From 50.0 min to 60.0 min, the...
  26. L

    Experiement of determining specifc latent heat of vapourisation

    Homework Statement Explain why heat loss is the same in both cases, provided the time is the same. Homework Equations VIt = mL + H The Attempt at a Solution Is it the same because in both cases I'm asked to boil off 50g of alcohol?
  27. Y

    Latent Heat + Specific Heat Problem

    Homework Statement Suppose molten (liquid) lead, mass ml = 9.83 kg, is at its melting point. The lead is poured into water of mass mw = 585 g and initial temperature Tw = 16.2 C. Find mwb, the amount of the water that boils. NOTE: Reaching the boiling point is not enough; the question asks...
  28. D

    Calculating the Initial Height of a Hailstone for Complete Melting on Impact

    Homework Statement Assume that a hailstone at 0◦C falls through air at a uniform temperature of 0◦C and lands on a sidewalk also at this temperature. From what initial height must the hailstone fall in order to entirely melt on impact? The acceleration due to gravity is 9.8 m/sec2 and the...
  29. W

    How Much Ice Remains When Water and Ice Reach Equilibrium in a Styrofoam Cup?

    A styrofoam cup contains 2.00x10^2 g of water at 21.0°C. A student adds 60.0g of ice at 0°C into this cup. Determine the mass of ice in the cup when the ice-water mixture reaches equilibrium. Qcold = -Qhot no idea where to start
  30. P

    Temperature of resistor in latent heat experiment.

    Hi, I have conducted an experiment for finding the latent heat of liquid nitrogen using a 5W power supply and a 200 ohms resistor. As part of my conclusions I am asked to discuss/refer to the resistor's temperature during the experiment. I am not sure whether I am expected to provide a...
  31. N

    Relationship between Latent Heat of Fusion and Temperature

    Does latent heat of fusion typically go up or down with temperature? I'm trying to calculate the amount of pressure needed to move the melting point of Thorium Dioxide up by 444 degrees kelvin using the Clausius-Clapeyron Law to see whether it would be feasible to line the combustion chamber of...
  32. A

    Heat and phase change: latent heat

    Homework Statement A 42kg block of ice at 0°C is sliding on a horizontal surface. the initial speed of the ice is 7.3 m/s and the final speed is 3.5m/s. Assume that the part of the block that melts has a very small mass and that all the heat generated by kinetic friction goes into the block...
  33. K

    Finding the specific latent heat of fusion of an ice cube

    Homework Statement We completed a lab with the following information Substance Mass(g) Starting temperature (°C) Final Temperature (°C) Ice cube 15.55 0 12 Water 151.25 21 12 Now...
  34. S

    Pressure affecting the latent heat of vapourization

    Homework Statement The definition of latent best of vapourization is the amount of thermal energy required to change the state of a liquid to a gas or vice versa. Also, when we increase the pressure of the gas on the liquid there has to be more work done against the surroundings so the latent...
  35. M

    Enthelpy of Vaporization vs. Latent heat of vaporization

    I am having confusion with the difference between these two, or are they synonymous terms?
  36. L

    Latent heat of vaporisation question

    Homework Statement A pupil performing an experiment finds that, when the heat supply is 16W, it takes 30 mins for the temp of the water to rise from 20°C to 100°C, and that the rate of evap is very slow even at the latter temp. Estimate an upper limit to the value of the heat capacity of the...
  37. S

    How long to melt the ice(heat, heat transfer, latent heat)

    The graph is in the attachment! ( don't have to download to view the file)Homework Statement 49a) A 0.25 kg piece of ice is warmed by an electric heater and the following graph of temperature is produced. Assume that there has been no loss of energy to surroundings. How much additional time...
  38. S

    Changes of state , latent heat and heat transfers

    Homework Statement What is the total amount of heat required to heat a 0.2 kg of ice from a temperature of -20 degrees to a temperature of 30 degrees Celsius Homework Equations Q=mcΔt Q=mLf Q=mLv The Attempt at a Solution To solve this they break it down, almost like a...
  39. K

    Latent heat and final temperature

    Homework Statement An aluminum container whose mass is 205g contains 300g of water at 20°C. In this container is then placed 250g of iron at 150°C and 20g of ice at -10°C. Find the final temperature of the mixture. Given: mAl=205g mH2O=300g TAl1=TH2O1=20°C mFe=250g mice=20g TFe=150°C...
  40. S

    Latent Heat and phase changes (difficult)

    Homework Statement 10g of ice at 0 degrees Celcius is combined with 2 g of steam at 100 degrees Celcius. Find the final temperature of the resulting water. Homework Equations mc(Tf- Ti) m(Lf) or m (Li) The Attempt at a Solution ΔQice=mLice+mcwaterTf...
  41. M

    Latent heat, liquid-gas transition, stat mech with gravity

    Problem solved.Homework Statement The boiling point of a certain liquid is 95OC at the top of a mountain and 105OC at the bottom. Its latent heat is 1000 cal/mole. Calculate the height of mountain. It's Q4 of chapter 15 in Statistical Mechanics by S.K. MaHomework Equations it should be the...
  42. H

    Chemical potential in thermodynamics to find latent heat of vaporization

    Doing some fun problems in Keith Stowe's 'An Introduction to Thermodynamics and Statistical Mechanics'. Good book. Problem statement: A certain material vaporizes from the liquid phase at 700 K. In both phases, the molecules have three degrees of freedom. If u_{0} in the liquid phase is...
  43. H

    Latent Heat (enthelpy) of Fusion changes with Pressure?

    If the melting point depends on the pressure, does the latent heat of fusion also depend on the pressure? The equation relating the entropy of fusion to the enthalpy of fusion is given by: \Delta H=T\Delta S where T is, apparently, the temperature of melting. So, if the melting point...
  44. H

    How Do You Calculate the Final Temperature of Ice Tea Mixing Hot Water and Ice?

    Homework Statement 215 cm3 of hot tea at 95°C are poured into a very thin paper cup with 40 g of crushed ice at 0°C. Calculate the final temperature of the "ice tea". (Hint: think about two processes: melting the ice into liquid and, maybe, warming the liquid.) Homework Equations 0 =...
  45. P

    Latent Heat, Some Density, and God knows what else

    I've been having trouble understanding this second semester of physics thus far. I've done SHM pretty well, but this stuff is just strange to me. So here are the problems verbatum, but i'll fill out the template below to help ease the pains. For problem 1: Homework Statement The heating...
  46. S

    Latent heat vaporization vs fusion

    Why is the latent heat of vaporisation greater than that of fusion(melting)? I mean in liquid state,atoms are already far apart, so it must require less energy to make them gas(far apart) as forces(electric in nature) between molecules decrease with distance.
  47. L

    Calculating Latent Heat of Vaporisation: 3 kW Kettle, 2.0 kg Water @ 100oC

    A 3 kW kettle contains 2.0 kg of water at a temperature close to 100oC. Latent heat of vaporisation for water: Lv=2256 (kJ kg^-1) Q= Lv x mass Ok I understand this problem because I now the answer but I don't understand the process. Like my teacher wrote 2256x10^3 why he wrote...
  48. S

    Determining latent heat of fusion of ice

    Homework Statement For the problem below I was able to work out part (i) but I am stuck on working out part (ii) I tried using information given but was unsuccessful. Can anyone help me out? An insulated copper container of mass 0.250 kg contains 0.350 kg water. Both the container and the...
  49. P

    Question related to latent heat of fusion of ice

    Homework Statement one gram of ice at 0 degree C contracts in volume by 0.091cc on melting. 9gm of a metalis heated to 200 degree C and dropped into and ice calorimeter. The decrease in volume was found to be 0.0182 cc. Calculate the Sp. heat of the metal (ANS:0.09cal/gmC) Homework...
  50. F

    Specific & Latent Heat - Heat required to turn water in Aluminum Tray -> Ice

    Specific & Latent Heat - Heat required to turn water in Aluminum Tray --> Ice Homework Statement 200 g Water (l) is contained in an Aluminum ice tray that has a mass of 340 g. Both is at 18°C. How much heat (Q) must be removed to turn the water into ice at -15°C? Aluminum mAl= 340g...
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