Questions tagged [heat]

For questions about heat - a form of transfer of energy from one body to another or from one body to its surroundings. Also see these tags: [thermodynamics], [enthalpy], [energy], [temperature].

Heat is a form to transfer energy from one body to another or from one body to its surroundings. It is closely connected to (), , , change in the state of matter, .

For example, the transfer of heat, i.e. heating, may cause the temperature of a system to rise.

Heating may also result in a change of the state of matter:

  • melting: $\ce{H2O_{(s)} (ice) ->[\Delta T] H2O_{(l)} (water)}$ (see also )
  • : $\ce{CO2_{(s)} ->[\Delta T] CO2_{(g)}}$
  • boiling: $\ce{W_{(l)} ->[\Delta T] W_{(g)}}$ (see also , here $\approx 6200~\mathrm{K}$)

The symbol of heat is $q$ or $Q$ and it is usually measured in joule $\mathrm{J}$.

482 questions
49
votes
9 answers

Why does ice water get colder when salt is added?

It is well known that when you add salt to ice, the ice not only melts but will actually get colder. From chemistry books, I've learned that salt will lower the freezing point of water. But I’m a little confused as to why it results in a drop in…
cspirou
  • 607
  • 1
  • 5
  • 4
28
votes
3 answers

What properties of carbon dioxide make it a greenhouse gas?

Why is it that heat from the Earth reflects back off carbon dioxide and other greenhouse gases but not gases like nitrogen or oxygen?
Charlie
  • 487
  • 4
  • 8
28
votes
5 answers

Microwaving a glass of water, what happens?

Most of us here would already know the simplified idea behind microwaving food: Microwave radiation hits the water molecules present in food, which excites them and causes 'em to vibrate rapidly in situ resulting in the heating up of food. Very…
paracetamol
  • 18,297
  • 26
  • 102
  • 166
28
votes
2 answers

When a candle burns, why does the top of wick glow if bottom of flame is hottest?

Totally an elementary question. Staring at a candle, it appears that the bottom of the wick is dark whereas the top glows. However the bottom of the flame (the blue) is the hottest. Is the reason for this that the concentration of liquid wax is…
ZAR
  • 391
  • 3
  • 5
26
votes
2 answers

Why does diamond conduct heat better than graphite?

Our teachers made us accept (without any explanation) that diamond conducts heat better than graphite. What is the reason behind this (alleged) fact?
mepkn
  • 385
  • 1
  • 4
  • 8
22
votes
1 answer

If aliens lived in a hydrogen (or any flammable gas) based atmosphere, would they perceive oxygen to be flammable?

Energy, fuel, and oxygen are needed for a fire to burn. In a hydrogen chamber, if there was a pipe spewing small amounts of oxygen, could you light the oxygen on fire as it began to mix with the hydrogen?
22
votes
3 answers

Why does milk overflow when boiled?

I was wondering that like whenever I boil milk I just have to keep standing in front of it to make sure that I don't waste any milk but then I was wondering like Why does it even overflow ? In case of water it doesn't happen. What makes it to behave…
Shashank
  • 1,493
  • 5
  • 17
  • 26
21
votes
4 answers

What is the origin of the maximum in rotational heat capacity?

The graph of rotational heat capacity above shows a small maximum before approaching the equipartition value. What is the origin/physical explanation of this maximum?
218
  • 455
  • 3
  • 8
20
votes
6 answers

What exactly is temperature?

I've read at many places that temperature is the average kinetic energy of particles present in an object. I just don't intuitively get how kinetic energy is connected with temperature. And how is heat connected with temperature then? Then what…
19
votes
3 answers

How to evaluate the heat of formation with computational chemistry?

I'm sorry if this is a stupid question, but since I'm a beginner with computational chemistry, please, be patient. Let's consider the reaction of formation of water: $$\ce{1/2 O2(g) + H2(g) -> H2O(g)}$$ This reaction shoud give a $\Delta_\mathrm…
HCSthe2nd
  • 465
  • 4
  • 17
17
votes
2 answers

Why is the specific heat of water high?

How is the specific heat of water so high? I was reading the hyperphysics article on it but could not understand it properly.
Paul
  • 275
  • 1
  • 2
  • 7
16
votes
6 answers

Is there a cheap, safe liquid that evaporates EXOthermically around room temperature?

The heating and AC system in the building where I occasionally work, works like this (basically a thermostat): The administrators set some temperature that is maintained automatically. Say, in the winter, the outside temperature is 0 °C. The admins…
iammax
  • 999
  • 8
  • 16
16
votes
9 answers

How can 30 ml of water be heated in less than 10 seconds?

How is it possible to heat a tiny amount (30 ml)[1] of water to a high enough temperature to make a coffee, in less than 10 seconds and possibly instantly? Most heaters that I know of heat water in no less than 90 seconds (induction heater) or 3…
Alper Turan
  • 271
  • 1
  • 2
  • 8
15
votes
3 answers

Why is the enthalpy change not zero in an adiabatic process?

Which of the following must be true for adiabatic processes? $C_V = C_p$ $\Delta H = 0$ $\Delta U = 0$ $\Delta S = 0$ $q = 0$ (Source: Chemistry GRE) The answer is $q = 0$. From what I can find, an adiabatic process is when there is no transfer…
halcyon
  • 1,088
  • 1
  • 10
  • 26
15
votes
2 answers

Heats of combustion and stability of rings

Which isomer would have the largest heat of combustion? A) Propylcyclopropane B) Ethylcyclobutane C) Methylcyclopentane D) Cyclohexane E) Since they are all isomers, all would have the same heat of combustion. Can anyone explain why? If you think…
yolo123
  • 1,845
  • 3
  • 22
  • 37
1
2 3
32 33