What is Heat energy: Definition and 91 Discussions

In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter. The various mechanisms of energy transfer that define heat are stated in the next section of this article.
Like thermodynamic work, heat transfer is a process involving more than one system, not a property of any one system. In thermodynamics, energy transferred as heat contributes to change in the system's cardinal energy variable of state, for example its internal energy, or for example its enthalpy. This is to be distinguished from the ordinary language conception of heat as a property of an isolated system.
The quantity of energy transferred as heat in a process is the amount of transferred energy excluding any thermodynamic work that was done and any energy contained in matter transferred. For the precise definition of heat, it is necessary that it occur by a path that does not include transfer of matter.Though not immediately by the definition, but in special kinds of process, quantity of energy transferred as heat can be measured by its effect on the states of interacting bodies. For example, respectively in special circumstances, heat transfer can be measured by the amount of ice melted, or by change in temperature of a body in the surroundings of the system. Such methods are called calorimetry.
The conventional symbol used to represent the amount of heat transferred in a thermodynamic process is Q. As an amount of energy (being transferred), the SI unit of heat is the joule (J).

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  1. V

    B Heat exchange after thermal equilibrium

    In screenshot below, systems A and B are separated by an adiabatic wall initially while each of them exchanges energy with system C via a diathermic wall. Once A and B reach thermal equilibrium with C, then A,B are allowed energy exchange via a diathermic wall, and energy exchange between A and...
  2. G

    B Does Light Energy contain Heat Energy in a large scale?

    Can I understand that light energy contains heat energy? or Do I have to separate between two concepts? because light energy from the sun makes heat energy after absorption of molecular?
  3. V

    Temperature rise without heat energy?

    If I look at the specific heat equation mentioned, then I would be inclined to think that without heat energy being added to the gaseous mass its temperature cannot rise. But, if some form of energy like chemical energy in gaseous mass could be directly converted to internal energy of the same...
  4. E

    How to find the heat energy produced in a resistor?

    i found current to be 2/5 A. then 2/5A multipled by 6s = 2.4C. and since one joule per coulomb is equal to the unit of p.d, i get 2.4J. I don't get 4.8J(supposed answer)
  5. D

    Heat Energy Intercepted by the Earth

    I've recently been interested in how much energy the Earth intercepts from the Sun; the answer, unsurprisingly was an astronomical amount, measuring quite easily into the ZetaWatts. However, the maths that got me that answer got me thinking... you can use the same method to determine the amount...
  6. thaiqi

    Why doesn't the atom absorb heat energy when it is low?

    (In my last thread) Mentor Dale said: " An atom in the ground state can absorb energy from the environment including thermal radiation. Once it has done so it will be excited and will no longer be in the ground state. An excited atom can radiate and go to a lower energy state, but an atom in the...
  7. M

    Heat Energy and Power -- Heating ice in a copper pan

    Homework Statement Calculate the power needed to heat a 1360 gram chunk of ice in a 600 gram copper pan from 0 ◦C to the system’s final temperature of 35◦C in a time of 10 minutes. Homework Equations Q=mcchange in temp Q=mLf P= energy/time The Attempt at a Solution I thought that adding the...
  8. M

    Conservation of energy (Waterfall)

    Homework Statement In a waterfall about 20 billion liters of water per hour drop about 110 m. What is the increase of the water temperature, assuming that the entire gain of heat is transferred to the water? Homework Equations I'm more curious about the question in itself. Perhaps I'm missing...
  9. Aleoa

    Understanding the Heat Energy of Springs: Exploring Feynman's Explanation

    In an ideal reversible case, a spring is a simple perpetual machine ; in order to introduce the slowdown of a spring in a real case and the consequent heat development in the spring, Feynman writes (here par. 4.4): "Inside a spring or a lever there are crystals which are made up of lots of...

    Can black body retain it`s absorbed heat energy?

    Can black body retain it`s absorbed heat energy? If yes, then why we can not convert this energy into a usefull form such as into electric energy as solar do?
  11. Franz Rojas Ayala

    Heat energy input from a hot source in a heat engine

    Greetings! I did the famous "Mass Lifter Heat Engine" experiment in which a mass is put at the top of a piston enclosed within a cylinder. The cylinder is connected to an aluminium canister of air and the air inside this canister expands and contracts the piston with thermal contact. We had 2...
  12. D

    Does capillary action use water heat energy?

    Capillary action is a form of work, i.e. an object (water) moved by a force (capillary action) over a distance. Since all work requires energy, what supplies the energy for capillary action? Is the chemical energy of the water increased by adhering to a surface? Perhaps the heat energy of the...
  13. Z

    I Heat energy: statistical mechanics vs atomic orbitals

    Normally, I prefer to do my own research, but I'm drawing a blank on this one. Any help would be appreciated. My understanding is that statistical mechanics accounts for all of the heat energy in a gas by the kinetic energy of the molecules. I also understand that atomic orbitals have different...
  14. V

    Examples of conversion of gravitational PE to heat energy?

    Homework Statement I was looking for some examples where gravitational potential energy is converted to heat energy. Are there many such examples of this conversion? I could only come up with one such example and even that could be an incorrect example. Homework Equations PEg = mgh The...
  15. V

    Heat energy in an inelastic collision

    Homework Statement A bolt of mass 0.3 kg falls from the ceiling of an elevator moving down with an uniform speed of 7 m/s. It hits the floor of the elevator (length of the elevator = 3 m) and does not rebound. What is the heat produced by the impact ? Would your answer be different if the...
  16. nickyfernandezzz

    Kinetic energy to thermal energy

    Hey guys, I need help with the following question. A lead ball of specific heat capacity 130J/KgK travels with a speed of 100m/s before it hits a wooden cube fixed to floor and gets stuck inside.What will be the rise in temperature of this lead ball by the time it comes to I attempted the...
  17. K

    Where does heat energy go when dissipated in metal?

    When heat is dissipated into a piece of metal(aluminum for example), what happens to the potential energy that was stored in the heat? Does it transform into another form of energy or is it absorbed by the atoms of the metal element?
  18. A

    Heat energy and liquid nitrogen boil-off rate

    Homework Statement Kindly refer to part (c). The woking should be power/0.35 (what I think according to the graph). But the answer is power (that is the answer of part b) divided by 0.02 Homework Equations I have used the ratio method simply The Attempt at a Solution According to part (b)...
  19. bebop1

    Kinetic Energy and Collision Question

    Homework Statement Why is there more heat and sound energy produced with a larger collision? Homework EquationsThe Attempt at a Solution Honestly no clue. I would really appreciate any help! Any videos would also help!
  20. A

    Heat energy from a charged configuration

    Homework Statement [/B] I have two spherical metallic shells with radius ##3a## and ##a##, the little one is placed inside the larger so that the center of the little one is at a distance of ##a## from the center of the larger. The outer one has a charge ##3Q## and the one inside has a charge...
  21. F

    Harness Heat Energy for Drone Power - How To?

    Is there a way I could harness heat energy in a drone, if so, how?
  22. M

    Find Heat Energy Needed to Expand Gas to Triple Volume

    Homework Statement When 0.40 mol of oxygen(O2) gas is heated at constant pressure starting at 0 degrees C, how much energy must be added to the gas as heat to triple its volume? (The molecules rotate but do not oscillate) Homework Equations pV=nRT p1V1/T1=p2V2/T2 Q=mcdT Value of Cp for Oxygen...
  23. Tom Rauji

    Heat energy extraction in turbocharger

    I have a question I've found asked, but never found answered. I'm an EE, but I have a car as a hobby. I changed from a belt drive inlet air compressor (supercharger) to a turbocharger. People commonly say the turbo is "much more efficient" because it "runs free on otherwise wasted exhaust...
  24. 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...
  25. A

    Heat energy dissipated between two conducting shells

    Homework Statement A conducting sphere of radius a is surrounded by a neutral conducting shell of radius b (b > a).Connections are provided as shown in diagram. Initially, the sphere has a charge Q. The switch S1 is opened and then closed. The switch S2 is then opened and closed. Finally, the...
  26. Jeevan Patnaik

    How are different forms of energy come into existence?

    What I understood so far is that whole universe was born from a single point at which there was no time (or all the time was at single point - no present, no future) and then a big bang happened (may be), creating time, energy, mass etc. I want to learn physics at much deeper levels. So, I...
  27. P

    Heat energy dissipated from moving box with friction

    Homework Statement A box of books that weighs 40N is dragged at a speed of 1.5 m/s across a rough floor. If the coefficient of friction between the floor and the box is 0.20, what is the rate at which heat energy is dissipated? Homework Equations Friction: f=μN Work: W=F*d Power: P=W/t The...
  28. J

    How much heat energy in molten glass?

    How much heat energy is in a cubic meter of molten glass? I would like to know how much energy would be lost if a cubic meter of glass would be allowed to cool, instead of turning the energy into something else.
  29. K

    Is Heat a Form of Energy Stored in a Body?

    Homework Statement Can i say a body has heat energy, like it kinetic or height energy? The next formula only shows the energy transfer in change of temperature Homework Equations Heat energy: ##E=c\cdot m\cdot\Delta t## The Attempt at a Solution I guess not, although it's obvious that the...
  30. C

    Solving Heat Energy Dissipation for a Falling Magnet

    Homework Statement A magnet of mass 0.10 kg is dropped from rest and falls vertically through a 35.0 cm copper tube. Eddy currents are induced, causing the copper to warm up. The speed of the magnet as it emerges from the tube is 1.50 m/s. How much heat energy is dissipated to the environment...
  31. S

    Specific heat capacity - heat energy transfer

    Homework Statement Find the mass of water that vaporizes when 3.39 kg of mercury at 243 °C is added to 0.476 kg of water at 90.0 ° Homework Equations q=mcT, q=mL The Attempt at a Solution When vaporising T=100degC. Heat lost by mercury = heat gained by water. 3.39kg x 139J/kg/C x...
  32. Hardik Batra

    Kinetic energy and heat energy of molecule?

    I know that . Average kinetic energy of a molecule is (f/2)kT (for translational motion.where f=3 ) In my textbook given that... If the degree of freedom of the gas molecule is f then the average heat energy of each molecule of the gas is = E(avg.) = (f/2)kT which is same as the...
  33. D

    Converting everyday heat energy into electricity

    Separate question. Can anyone tell me what the limitations would be of trying to convert the planet's ever increasing heat into electricity. I'm imagining building materials that could take 100-120 degree heat and convert it for use in running home appliances, including air conditioners. How...
  34. B

    Heat Energy Removed: Latent Heat of Sublimation/Fusion

    What is the heat energy removed from a liquid when vapor is no longer present. This has been bugging me all day. I was thinking latent heat of sublimation cause ice seems to just melt in a ice machine due to door opening and closing and heat from air . Next guess was latent heat of fusion
  35. A

    Preserving Heat Energy from Fridges: Alternatives & Ideas

    How can I preserve energy dissipated out from some devices that always extract heat like fridge? Do you guys have some alternatives or ideas to convert heat energy to electrical energy that can supply some sensors and indicators? Thanks!
  36. M

    How Heat Energy Transfers Through a Pan of Water

    "Explain how energy gets from the flame of a gas cooker to the contents of a pan of water above the flame". This has stumped me...I've only got as far as the metal pam conducting heat energy, but them I don't know why it is transferred through the water...?
  37. B

    Heat energy change when gas compressed

    Homework Statement One mole of an ideal gas is in a container with a moveable piston. A 100 N force moves the piston down 1 m; the compression is isothermal. Does 100 J of energy leave the gas or enter the gas? Homework Equations W=Fd U=Q-W=Q-P(Vf-Vi) The Attempt at a Solution...
  38. H

    Converting heat energy to electrical energy

    I'm going to ask a very basic question and my attempt at solving it may not even be right. Electricity is basically flow of electrons in a conductor, so what I was wondering is if I start heating the wire the atoms will start losing the electrons and everything will be moving in a chaotic way...
  39. C

    Heat energy from Enthelpy of formation

    Homework Statement I'm doing physics and I don't know if this counts as physics or Chemistry (sorry if this does not belong here) Homework Equations \Delta H = \Delta U + P \Delta V \Delta U = Q + W The Attempt at a Solution So firstly I started off with ## \Delta H = \Delta U + P \Delta...
  40. K

    Calculate Heat Energy Req'd for 0.1 kg Ice -30°C to 0°C

    Homework Statement Calculate the heat energy required to convert 0.1 kg of ice at -30°C into water at 0°C. The specific heat capacity of ice is 2100 J kg-1K-1 and the latent heat of fusion of ice is 3.25 x 10^5 J kg-1 Homework Equations e=mcθ The Attempt at a Solution So first i...
  41. D

    Concept to extract heat energy from objects

    I was just thinking about absolute zero temprature roughly -250 c degress Lets say an object has a room temprature of 20 degrees celcius Doesnt it mean i has a lot of thermal emegy So i used the equation H= Cp x M x ΔT H = Heat energy (in Joules) m = mass (in kilograms) delta T =...
  42. J

    Heat energy in a mixture to get final temperature

    Homework Statement A glass mug has mass 125g empty. It contains 180g of coffee. Both are at 70 C. I add 15g of creme at 5 C. Find final temperature. Assume creme has specific heat of 2900 J/kg.C . Homework Equations Q = m C (delta)T in joules or Kcalories m = mass in kg...
  43. R

    Specific Heat Capacity, Heat Energy, Thermodynamics Physics

    Homework Statement A block of ice has a mass of 150g and a temperature of -4°. The ice is melted by supplying 60KJ heat energy. Determine the final temperature of the melted water. Homework Equations Equations i think can be used: Q = ml and H = mcΔθ The Attempt at a Solution...
  44. V

    What to solve for in specific heat energy problem

    Homework Statement You have a position working with a group investigating biological mechanisms that determine a predisposition to obesity. Your assignment is to measure the rate that energy is output by certain types of cells when a nutrient is introduced. To begin this study, you have...
  45. Y

    Rate of reactions vs. HEat energy evolves per second inititally

    Nitrogen dioxide reacts with carbon monoxide by the overall equation: NO2(g) + CO(g) ----> NO(g)+ CO2(g) At a particular temperature, the reaction is second order In NO2 and zero order in CO. The rate constant is 0.515 L/(mol*s). How much heat energy evolves per second initially from 3.50...
  46. S

    GSHP - What percentage of heat energy is taken from the ground?

    Hi all, I am wondering about heat pumps, not necessarily ground source heat pump. What percentage of heat is taken from the ground? My understanding was that 100% of the heat is taken from the ground but it costs 25% (if COP of 4) in electrical energy (running the compressor) to...
  47. G

    Calculate Heat Energy Transferred for Isobaric Expansion

    Homework Statement A cylinder with a frictionless piston contains 0.05 m3 of gas at 60 kPa. The spring holding the piston is now in tension. The cylinder is heated until the volume rises to 0.2 m3 and the pressure rises to 180 kPa. Assuming no losses in the system, and the force on the...
  48. C

    Freezing Lake - Heat Energy Questions

    Homework Statement Freezing Lake A small pond has a layer of ice 1cm thick floating on its surface. The air temperature is -10°C. Steps (a-c) should help you find the final answers in (d) and (e). (a) What is the temperature of the liquid water just below the ice? (b) Write the...
  49. K

    Final Temperature of Drink After Adding Ice Cubes

    Homework Statement A 25 g glass tumbler contains 350 mL of water at 24°C. If four 20 g ice cubes each at a temperature of -3°C are dropped into the tumbler, what is the final temperature of the drink? Neglect thermal conduction between the tumbler and the room. Homework Equations Q = mcT Q =...
  50. M

    How heat energy creats photon and how it jump to other atoms?

    Hi Friends, I am not expert in atomic science but very interested. I have few questions. I hope some one may help me to understand better. 1. Light (photon) appears when electron jump from one level to another level due to heat energy. 1a). Is the heat affects only outer level...