Heat Definition and 1000 Threads

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. J

    What is the molar heat of self-decomposition of nitric acid?

    I am curious as to what is the value of the molar heat of self-decomposition of nitric acid. I've searched online and cannot seem to find the above value. Essentially, I am looking for the value for anhydrous nitric acid although I am aware that the acid is generally not provided in pure...
  2. J

    What is the heat of combustion of 1 kg carbon dioxide w/ magnesium?

    I am trying to find out the heat of combustion of one kilogram of carbon dioxide with magnesium. I am looking for results for stochiometric conditions of these two reactants. I have found the following equation online 2 Mg(s) + CO2 ---> 2 MgO(s) + C(s) yields a standard enthalpy of --810.1...
  3. F

    Pulling a vacuum on a heat pump with a recovery machine

    I am a student attending an HVAC program at a trade school. Today I recovered refrigerant out of a heat pump in order to debraze the compressor out of the heat pump. My instructor has taught me how to use a recovery machine to recover refrigerant out of an air-conditioner or heat pump before...
  4. GuillemVS

    Electromagnetic Waves and different energy manifestations

    When an object is hot its particles are moving faster than when is cold, right? I've searched that particles are electrons and protons, so it means that if we warm a object the electrons will be moving or even accelerating. Every charge accelerated creates Electromagnetic Waves (or light)...
  5. F

    A 3D Heat equation with elementary Dirichlet BC

    Hi, I am looking for the solution of the following heat conduction problem (see figure below): the geometry is the semi-infinite domain such that (x,y)∈R2 and z∈[0,∞[ ; the thermal diffusivity is constant; the domain is initially at a temperature of 0; At t>0, a small square of the surface...
  6. D

    Why is a two-layered design recommended for heat insulation experiments?

    I'm doing some experiments on heat insulation with a model house (made of styrofoam, 3cm), heated with a 25W light bulb. In some papers I have read that it's important for the box to be two-layered, with only the outer layer being styrofoam and the thin inner layer consisting of material with a...
  7. C

    Tricky heat calculation from the 1850s

    Hi everyone ! I'm calling for help, for I have been unable to make sense of 1850s calculus ! In the Mechanical Theory of Heat, R. Clausius introduces the mathematical expression of internal energy by investigating an infinitesimal Carnot cycle (that is to say all volume variations are...
  8. M

    B Experiment reverses the direction of heat flow

    I hope this is the correct section to post this but I found it very is interesting Link to original article: https://phys.org/news/2019-06-reverses.html Quotes from the article: "We investigated temperature changes in the spins of the nuclei of the hydrogen and carbon atoms. The chlorine...
  9. Superposed_Cat

    How can C4 be detonated by heat or shock, only by electricity?

    I was thinking about electroactive polymers, and wondering if any exist that are immune to high temperatures, and although explosive decomposition is a completely different subject, it got me thinking about c4. Chemically speaking, what gives a compound such as c4 the ability to not detonate...
  10. Nikhil Rajagopalan

    Molar specific heat capacity for constant volume.

    Dear Experts, We compute Cv for gases using the idea of equipartition principle and degrees of freedom. In case of a diatomic molecule, there are minimum 3 degrees of freedom (at very low temperatures) and maximum 6 degrees of freedom one of them being vibrational (at high temperatures. Does it...
  11. dRic2

    Heat transfer in a nuclear reactor and the electrical equivalent

    To write the equation I took as the control volume the following block: and the equation I wrote are: $$ 6m_{f} c_{p_{f}} \frac {dT_{f}}{dt} = 6P - \frac 1 {R_1} (T_f - T_g) \text{ for the fuel}$$ $$ m_{g} c_{p_g} \frac {dT_{g}}{dt} = \frac 1 {R_1} (T_f - T_g) - \frac 1 {R_2} (T_g - T_c)...
  12. C

    Can gas kinetic theory explain heat transfer from gas to a container?

    If one considers the kinetic theory of gases, can a first order estimate of thermal transfer be performed by considering momentum exchange at the container's surface? I understand the basics of explaining and calculating pressure with the kinetic theory of gases, but if we assume energy is...
  13. JD_PM

    Heat engine undergoing an elliptical cycle

    An ideal diatomic gas undergoes an elliptic cyclic process characterized by the following points in a ##PV## diagram: $$(3/2P_1, V1)$$ $$(2P_1, (V1+V2)/2)$$ $$(3/2P_1, V2)$$ $$(P_1, (V1+V2)/2)$$This system is used as a heat engine (converting the added heat into mechanical work). Evaluate the...
  14. HumanistEngineer

    A Solving the Convection-Diffusion Equation for this Pipe with a Heat Sink

    Hi Again, I try to solve the transient temperature propagation through a buried insulated pipe by means of solving the convection-diffusion equation with a heat sink that is the heat loss from the water mass to the ground. Below you can see the details of my calculation steps in my numerical...
  15. T

    Heat capacity vs Thermal conductivity in a LN2 bath

    I worked on a lab experiment that was meant to measure heat capacity but left me with some other questions. The students measured the mass of a cup of liquid nitrogen as it boiled off, recording mass vs time. Then they drop a solid object into the bath, one experiment with a small bit iron...
  16. D

    Can someone please debunk this claim that CO2 does not trap heat?

    Hi everybody I follow climate denier pages and every now and then come across a claim that doesn't seem to have been debunked yet. One such claim is made here: <link to uacceptable source deleted> The gist of the article is that scientists experimented with using different gases in double...
  17. heatupgrade

    Can we make electricity from heat?

    I am a refrigeration technician with a fascination for heat pumps. I wonder if we can make two systems in parallel. The Carnot heat engine is used to describe the steam locomotive. I want to use a different fluid with a lower boiling point to create a heat engine using a refrigeration cycle...
  18. santimirandarp

    Isothermal expansion of a gas: heat of surroundings

    In an isothermal process, for an expanding gas ##\Delta U_{sys}=0## and ##Q=-W## but then, How can we evaluate ##Q_{surr} ##? It should be ##Q_{surr}=-Q_{sys}##, but I don't know how to show it in equations. If I try to get the result through the principles: ##\Delta U_{sys}=-\Delta U...
  19. santimirandarp

    Understanding q: Why does dqsurr = -dqsys?

    The question is: why ##dq_{surr}=-dq_{sys}##? q=heat, surr=surroundings, sys=system. Is there any simple way to understand this?
  20. didaw

    The efficiency of a furnace’s heat transfer process

    If I am honest with you I don't even know where to start, if someone wouldn't mind helping me find a starting point? Additional information Melting point of aluminium 660°C Specific heat capacity for aluminium (cp): 0.91 kJ/kgK...
  21. saratavares

    Heat exchangers and energy balances

    I have to do a project using Aspen and need to do some math before hand. Can you please help me? Here's the problem: A heat exchanger with 10 m2 of heat transfer area is provided to supply 58 kW to a water stream available at 15 ° C and 1 bar. The available hot fluid is freon-12 at 32 ° C and 7...
  22. A

    I Is there a limit to how hot something can get, and if so why?

    Question in the title .
  23. R

    Heat transfer to solution per litre

    Problem Statement: This is a question I made up to understand more about the calorimetric power. The equation below is given by Koda et. al (2003). A saucepan of water (400 mL) on a stove is been heated at constant temperature. The calorimetric power can be written:##Power(W)= (\frac{dT}{dt})...
  24. W

    Calorimetry Lab Analysis (predict specific heat of unknown metal)

    Problem Statement: so we did an experiment. basically the teacher gave us each a cube of unknown metal and we had to figure out what it was using the specific heat. we put the metal in boiling water until it was 212C and then we put it in room temp water and we measured how much it heated the...
  25. S

    Heat transfer along the joint bar with one side diffusion-convection

    There are similar problems with heat conduction only where for example, right side of the bar also has a certain temperature or in-contact with a hot material. However, in this case diffusion and convection occurs on the right side of the bar, more precisely on the Y material. I guess we have to...
  26. 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...
  27. E

    Heat Storage Capacity of CO2 molecules

    I am a science hobbyist and working on a paper to illustrate the impact of CO2 on Global Warming. Question – What is the Storage Capacity in joules, of one molecule of CO2 @ 20c/68f/293k. In other words, what is the maximum amount of IR energy that one molecule of CO2 can store at this...
  28. D

    Thermodynamic possiblity for outlet temperatures of heat exchanger

    I have a heat & mass balance diagram wherein there is a shell and tube heat exchanger to recover heat from hot exhaust gas using cold water. The exhaust gas inlet temperature is 120°C and the outlet is at 40°C. The inlet water temperature is 35°C while the outlet water temperature is at 50°C...
  29. sww_world

    Heat Capacity energy exchange problem

    Givens for water: m: 0.250kg of water TW : 95°C C=4180 Givens for mug: m=0.085kg TM : 19° c=107 Required: final temperature of water Analysis/Solution: Qreleased+Qabsorbed=0, q=mc▲t mw*cw*Tw + mp*cp*Tp = 0 (0.250)(4180) (T2-95) + (0.085)(107)(t2-19)=0 1045(t2-95) + 9.095(t2-19)=0...
  30. C

    Could somebody please explain the vapor compression cycle?

    Heat is taken from food in the refrigerated space to the evaporator which has evaporated (I am assuming saturated vapor) refrigerant flowing through it. My first stumble would be, if this is true, why doesn't the temperature increase for the fluid coming out of the evaporator (unless it is...
  31. J

    Definition of Heat and the First Law of Thermodynamics (discrepancy?)

    Zemansky defines Heat as : When a closed system whose surroundings are at a different temperature and on which diathermic work may be done undergoes a process, then the energy transferred by non mechanical means, equal to the difference between the change in internal energy and the diathermic...
  32. I

    How does radiation become heat?

    I'm confused on how something can absorb visible light and release heat. Specifically, I'm confused how the Earth absorbs visible light and emits IR + heat. I'm in a class (about global warming) for non-science majors and don't have much of a background in science, so I would appreciate...
  33. callie123

    Can constant electrical current heat water?

    Hi, I'm trying to make a realistic scene, in which water is kept under constant electrical charge. If the power is around 75 milliamps, and it's in a stream about twenty feet across by ten feet deep, would this affect water temperature? Thanks!
  34. Zeynaz

    Help with a heat transfer question

    This question is in a unit about emission and absorption, Atomic Physics So far, I calculated the Power that the person gives off which is by using the S-B law formula. P= (s-b constant)*1.8*305K^4= 883 W (or Joules per second) for the ambient i used the same formula and found P= 702 W I...
  35. seb7

    Two or three types of heat transfer?

    Heat transfer: Conduction - Convection - Radiation, but I was wondering if conductive transfer is actually radiation transfer, but at contact distances; well not really contact since no material actually touches each other (at a quantum level). So, is conductive heat actually being...
  36. Zeynaz

    How Do I Calculate Temperature in a Thermodynamics Problem?

    So, I converted the V (milk) to m3 and found 1.8E-4 m3 and i already know the density so i found the mass of the milk in the bottle. Mmilk= 1.9E-7 kg Normally i would try to connect it with the formulas above but i don't know temperature. I am not sure how i can connect the dots. Can...
  37. C

    For a throttling valve, why is it that temperature remains the same?

    For a throttling valve C.V analysis, I am wondering why is it known that temperature remains the same for ideal gases. I understand that using the energy balance equation, I end up with h1=h2. Pretty simple so far. By breaking down enthalpy into its components u1+P1v1 = u2+P2v2 I realized that...
  38. Clara Chung

    Question about Fermi energy and heat capacity of a Fermi gas

    Attempt:
  39. PCal

    Effectiveness to calculate the outlet temperatures of a heat exchanger

    Because the specific heat capacity is lower for the hot fluid: ε=(T_hi-T_h2)/(T_hi-T_C1 ) 0.82=(140-T_h2)/(140-15) 140-T_h2= 102.5 T_h2= 140-102.5=37.5° I'm not sure if I'm actually on the right track here, if I am this is as far as I've gotten. I can't seem to then find an equation to...
  40. J

    How Do You Determine Heat Capacity for Liquids?

    liquid melting point (degrees C) boiling point (degrees C) water (H2O) 0 100 sodium (Na) 98 883 Sodium-potassium(NaK) -11 785 Lead(Pb) 327 1749 I'm prettttty sure by consulting the literature means by using the above table… but if that's the case then how in the world do you find Cv...
  41. 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...
  42. H

    A Irreversible processes. Heat equation, diffusion equation

    Both the heat equation and the diffusion equation describe processes which are irreversible, because the equations have an odd time derivative. But how can these equations describe the real world when we know that all processes in nature are reversible, information is always conserved? But these...
  43. C

    What is the intuitive meaning behind the polytropic process.

    What does it actually mean from an intuitive standpoint? I don’t want to simply memorize the equation. What is it really and when can it be used? What is the usefulness of it? Thanks.
  44. C

    What is the difference between flow energy and boundary work?

    What is the difference between the two? Also, as another question, for enthalpy, is it correct to define it to be the sum of internal energy and flow energy or is there another understanding for it? Thanks in advance
  45. C

    Why is air in atmospheric pressure and room temperature a gas?

    This seems like a simple thermodynamics question but I would like clarification. So the absolute critical temperature is 132.5 K (-221.17 F) and the absolute critical pressure is 3.77Mpa (546.7 psi). I understand that for temperatures above the critical point, a pure substance undergoes an...
  46. C

    How does specific volume play its role in the phase diagram?

    So, I am casually sifting through a chapter in a thermodynamics textbook talking about the multiphase process that pure substances go through. I understand how the P-v and T-v diagram works and that out of the three properties (specific volume, temperature and pressure), two of them are...
  47. T

    Efficiency of a Heat Engine: How to Calculate Heat Transfer in a Monotonic Gas

    Homework Statement I am having an issue trying to decipher this question, as I am not sure if it a lack of knowledge on my half or there is an assumption I have to make. Homework Equations ##\epsilon=\frac{W_{total}}{Q_{in}}## The Attempt at a Solution My issue is calculating the heat...
  48. C

    Does temperature increase when water is boiling at 100C and pressure is increasing......?

    Does temperature increase when water is boiling at 100C in a closed system? I am picturing a scenario where I am boiling water in a pot to make pasta. However, I decide to close the pot as the water is still boiling. By doing this I am sealing away the system of study from the environment. Thus...
  49. M

    Calculate the amount of heat supplied to a gas

    Homework Statement 1kmol of multatomy(I hope you understand - gas with many atoms) gas is heated for 100K (conditions of free expansion). I have to calculate the amount of heat supplied to gas. I have no idea how to do it. The right answer is 3320kJ Homework EquationsThe Attempt at a Solution
  50. EastWindBreaks

    Heat exchanger - efficiency of the cycle

    Homework Statement Homework EquationsThe Attempt at a Solution Since we want the fluid to be in liquid state before entering a boiler, and super-heated water can only reach 374°C before entering super-critical state, suppose after the expansion, the temperature at point 3 is still higher than...
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