# Search results for query: *

• Users: erty
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1. ### Probability and statistical mechanics

(I didn't know where to put this one, so somebody will eventually move it, I predict...) This is a absolute newbie-question, so don't be evil! Why does statistical mechanics deal with probabilities? ASAIK, statistical mechanics is built on classical mechanics, where it is possible to predict...
2. ### Expansion of ideal gas into a vacuum

Well, that's the problem. I consider the box with the gas to be my system and everything else to be the surroundings/universe. But what if I turn it the other way around? If I consider everything but the box to be my system, and I pull up the partition, then I've applied work on the...
3. ### Expansion of ideal gas into a vacuum

This is Joule's experiment. He found out that the internal energy U of an ideal gas only depends on the temperature.
4. ### Expansion of ideal gas into a vacuum

I have a box divided by a partition. On one side I have n mole ideal gas, on the other side there's vacuum. If I remove the partition the ideal gas will expand into the vacuum. Since the box is adiabatic and no work is applied to or by the gas, \Delta U = 0. But what about the work used...
5. ### Understanding of irreversibility

Ok, thanks. Just had to be sure.
6. ### Understanding of irreversibility

The thermodynamic explanation of irreversibility - does it include the microscopic view of a process, i.e. the expansion of a ideal gas (the random movement of the molecules) or the melting of an ice cube? Or is it only defined within the macroscopic world?
7. ### Photons, energy and mass

Yes, I stand corrected. I changed "a photon/particle" to photons/particles, but forgot to correct the rest. Then how do I validate hf = mc^2, if it can't be applied to something like photons: they do have energy, but not any mass. Does this have something to do with the wave/particle duality...
8. ### Photons, energy and mass

These are some of the very fundamental things about the wave/particle-duality, I do not understand: 1) Do photons have a mass? 2) Do particles have a frequency? E = hf , how do I interpret this? 3) E = mc^2 and E = hf. I've seen these two equations combined into mc^2 = hf, indicating that...
9. ### The Photoelectric effect and classical physics

I figured it out. Thanks, everybody!
10. ### The Photoelectric effect and classical physics

Why can't waves have discrete values (E = hf applies to particles?)?
11. ### The Photoelectric effect and classical physics

Very good explanation. I'll dig into the physics stuff now that turdferguson and ZapperZ gave me some words to look up. Actually... no. I'm still in high school (or rather, the European equivalent) and this is my first year with physics. We're learning about waves at the moment, but this is...
12. ### The Photoelectric effect and classical physics

Hmm, I don't know anyting about it. Could you list a couple of words, then I'll try to look them up or google them
13. ### The Photoelectric effect and classical physics

The Photoelectric effect and "classical physics" The kinetic energy of the ejected electrons predicted by the classical physics should be related to the intensity of the light. According to experimental results, the kinetic energy of the electrons is proportional to the frequencies of the...
14. ### Oil, water and thermodynamics

@ definition of mixing I apologize for the confuzzlement. I did not know the distinction between the physical definition of mixing and the ... well, cook book's definition. This started when I mixed (oops) lemon juice and olive oil for a salad dressing, and the immiscibility thing made me...
15. ### Oil, water and thermodynamics

Many thanks to both of you. Now I do think I understand it, thanks for clarifying it!
16. ### Oil, water and thermodynamics

Yes, that makes sense.
17. ### Oil, water and thermodynamics

But how do you know that \Delta H = 0?
18. ### Oil, water and thermodynamics

Hmm, in your example the energy required to break the intermolecular forces (I.F. to make it easier) equals the energy gained when the new I.F. are formes, so deltaS = 0, then how can the reaction be entropy-driven? Apart from that, I understood the rest - excellent answer! Thanks.
19. ### Oil, water and thermodynamics

Why is deltaS < 0 when oil and water are mixed, while deltaS > 0 when water and alcohol are mixed? I mean, it is possible to explain this whole miscibility with polarity etc., but what is the thermodynamic explanation?
20. ### Oil, water and thermodynamics

Thanks. Then if I heat the veg. oil/water-mixture, it should be possible? H = U + pV, and I assume the volumerelated work doesn't matter, so pV ~ 0, therefore H ~ U. From G = H - TS, S > 0 when veg. oil and water are mixed together, so H < 0? That is a endothermic process, so in order to...
21. ### Oil, water and thermodynamics

If water and vegetable oil are added to a bowl, they do not mix. If gasoline and vegetable oil are added in another bowl, they _do_ mix. this has something to do with the polarity of the molecules, i.e. water is polar and gasoline and vegetable oil are unpolar. But is it possible to...
22. ### 2nd law of thermodynamics

Yes, but the \Delta S_{total} > 0, because the surroundings get warmer. (Or did I get this wrong?)
23. ### 2nd law of thermodynamics

I get it, thanks! \Delta S_{total} > 0, even though \Delta S_{sys} < 0, because \Delta H_{sys} < 0 according to the Gibbs energy and the conditions for a spontaneous process. Is it possible to calculate the \Delta S_{surroundings} , if I know the \Delta H_{sys} ? I mean, is there any...
24. ### 2nd law of thermodynamics

If \Delta H < 0 , then enthalpy is released from the system to the surroundings. It would make sense, if I had to add enthalpy ( \Delta H > 0, \qquad H = U + pV ) and the entropy decreased, but that's not true according to the Gibbs energy.
25. ### 2nd law of thermodynamics

Okay, then \Delta H = -100 \mbox{kJ} T = 1 \mbox{K} and \Delta S = -10 \mbox{kJ/K} because \Delta G = \Delta H - T\Delta S where T is constant.
26. ### 2nd law of thermodynamics

According to the 2nd law of thermodynamics, a spontaneous process will occur (or rather: is very likely to occur) if \Delta S > 0. A chemical process occurs if \Delta G < 0, where G = H - TS. Example: H = -100 kJ T = 1 K S = -10 kJ/K so \Delta G = - 190 kJ. In this example, \Delta...