difference between thermal and kinetic energy

NOTE:
As mentioned before, If you apply thermal energy (heat) to ice at -5 degrees until you have liquid water at +5 degrees. you have not increased the kinetic energy of the water during that time which you are applying energy and the water is melting (changing its state or increasing its potential energy)

Agreed.
Electromagnetic radiation is also another component of thermal energy.

Hi, andieje.

Lets keep it as simple as possible.

A molecule has various types of enery.

1) electrostatic = binds atoms together.

2)thermal = heat enery passed to the molecule enough to raise it above 0 kelvins (-273.5  O' celcius), so we know that all atoms on earth have thermal energy.

3) kenetic = this simply describes the moving energy a molecule or blob of molecules have and is equal to the 1/2 * Mass * Velocity ^2.

So an oxygen molecule at room temperature has thermal energy, it is moving (difusing through the air), so it has kenetic energy also. Anything that isn't moving has no kenetic energy.

confusion: thermal energy on a block of metal or on a gas, will convert some of it into kenetic energy. This doesn't mean the block of metal will shoot off, it is simply that the molecules that make up the metal move around more.

e.g. Thermal enery converts ice into water by converting the thermal in kenetic energy (vibrate bonds vigorous enough for them to break)

This is all very confusing to learn yourself as everyone gives different definitions. The two i gave above were both taken off the internet.

The reason I was thinking about the question in the first place is because i was reading about entropy and how

Ssurroundings = H / T

The explanation i read said:

"To understand why we have to divide by the temperature, consider the effect of very large and very small values of T in the denominator. If the body receiving the heat is initially at a very low temperature, relatively few thermal energy states are occupied, so the amount of energy spreading can be very great. Conversely, if the temperature is initially large, the number of new thermal energy states that become occupied will be negligible compared to the number already active."

This makes sense intuitively to me. This was taken off the website though whose definition of thermal energy you disagree with. It's for first year degree students so you'd hope it would be right too! Anyhow, I don't understand where potential energy would fit into this.  I understand that the more thermal energy there is in a system already, the less the entropy can increase by gaining more thermal energy. But the equation is only referring to energy that is proportional to temperature. Does this mean that the existing potential energy in the system makes no difference to the entopy change?

thanks

Please ignore my last comment. I am going to open a separate question about that. I think i need to clear up these definitions of thermal energy once and for all.

I am going to ignore electromagnetic energy for now if that's ok (but that was actually the other type of energy i was trying to remember)

I will stick with my defintiion of thermal energy as:

thermal energy is energy that can be transferred as heat in a disordered fashion by contact between molecules.

I have read that:

"Energy transfer as heat arises due to temperature differences between the system and the surroundings. This occurs until thermal equilibrium is reached (i.e. until all molecules have the same average kinetic energy)."

Is it correct to say, then, that the difference in temperature that causes heat transfer are due to differences in kinetic energy? But, as you have said previously that kinetic energy won't always end up as kinetic energy, it may become potential energy due to phase changes etc.

If the definition of thermal equilirium and objects having the same temperature is right, this means that systems in thermal equilibrium might not have the same thermal energy, only the same kinetic energy, because one system might have some thermal energy involved in a phase change. This seems counter intuitive.

Perhaps the correct definition for thermal equilibrium is that there is no further exchange of thermal energy and the systems need not have same temperature.

Kinetic energy is the energy associated with "momentum", and in simple cases is mv²/2.

Thermal energy is the energy associated with the bonding electrons of atoms. This is why electromagnetic energy is thermal energy. It also accounts for the fact that thermal radiation is "felt" in the infra-red region. Ie: we associate thermal energy with the infra-red region, although the energy is not frequency restricted.

Water is a polymer of H2O molecules - joined by H-O bridges. These bonds are held by the electron of the hydrogen atom being captured by the oxygen atom's outer shell. If this electron gets enough energy it will leave the s-shell of the hydrogen atom, and also the p-shell of the oxygen atom, since it has too much energy for that energy level. The effect is that the bond breaks. This happens at 100°C. At this temperature the water polymer molecules break up on absorbing energy and the water turns to steam. Note that the total kinetic energy of the molecules before and after this event is constant. The amount of heat needed to break these bonds is called the latent heat of vaporisation.

All elements except the rare gases have bonding electrons which make the elements stick together more or less tightly. The metals in fact have so many free bonding electrons that they can be used to conduct electricity, and, are therefore difficult to melt.

Water is a very good example of where inter-molecular bonding has changed the property of the substance from what one might expect. The molecular weight of water is 18 (2*H + O) which is the same as methane (4*H + C) but water boils at 100°C whereas methane boils at minus161.6 - a two hundred and sixty degree difference!

>>I always get confused about the difference between thermal and kinetic energy

To be absolutely clear and precise there is no difference. Thermal energy in thermodymanics is defined to include the kinetic energy, the chemical energy, the bond energy and so on. My explaination above was designed to explain how the thermal energy in terms of latent heats occurs.

Here are some thoughts on your question. These comments ramble a bit but might be useful. Quotes are used in appropriate places.
This is all very confusing to learn yourself as everyone gives different definitions.
Indeed they do, the definitions used have varying purposes and varying degrees of simplification. Also the providers have various degrees of understanding.
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 The two i gave above were both taken off the internet.
And sometimes the internet is wrong
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Thermodynamics is a complicated subject and can be approached in varying degrees of rigor. You will not be able to learn it on this site. You can get good answers to very specific, well worded questions. Discussions will inevitability diffuse and eventually become confusing. For discussions, read one or more well recommended books.
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I always get confused about the difference between thermal and kinetic energy.
You and lots of other people
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I have 2 definitions of thermal energy that I normally remember.

1) Thermal energy is the portion of energy of a moleucle that is propertional to its temperature
2) thermal energy is energy that can be transferred as heat in a disordered fashion by contact between molecules.
They are fine in their range of applicability but consider 1) and a single molecule. What is its temperature?!? It has none.
Consider 2) it says energy can be transferred as heat but what is heat? Some books and physics teachers think that the word is so confusing that they refuse to use the word heat.
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I think of kinetic energy as being the translational, rotational and vibrational energy of a molecule.
Good. But neither of your definitions mentioned kinetic energy.
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Here is the question you asked.
What other energy is thermal energy apart from kinetic?
You have gotten several specific answers, all very reasonable. (And also comments on several, but related, ideas of varying degrees of relevance.) The most compact and clear is from BigRat Thermal energy in thermodymanics is defined to include the kinetic energy, the chemical energy, the bond energy and so on
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If you are looking for concise, precise information one must be very concise and precise with the question. It is hard to do so but will avoid some confusion. Consider part of one answer
>>I always get confused about the difference between thermal and kinetic energy

To be absolutely clear and precise there is no difference. Thermal energy in thermodymanics is defined to include the kinetic energy, the chemical energy, the bond energy and so on.
That answer says that thermal and kinetic energy are the same and then goes on to show that they are different.

>>That answer says that thermal and kinetic energy are the same and then goes on to show that they are different.

You're right, aburr, I didn't put that very clearly. I meant to say that the one was contained in the other, and in that aspect, the one is a collective term, the other quite specific, they are different.

I should have been more precise. I apologise for that. I agree that I won't learn thermodynamics on this site. When ever i ask a question i end up being more confused as people answer the same question in different ways, probably because of, as you say, the varying degrees of rigor. I have 3 different thermodynamics books and they all say different things too.

I need to start this question again really but be a lot clearer about it.

thanks