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173 votes
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Why is absolute zero unattainable?

There was a story in my days about a physical chemist who was asked to explain some effect, illustrated by a poster on the wall. He did that, after which someone noticed that the poster was hanging ...
Ivan Neretin's user avatar
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80 votes

Why is absolute zero unattainable?

Absolute zero is a tricky concept, particularly once you start getting precise about it. Thermodynamics and quantum mechanics is a tricky business! I'll try to avoid the precise parts, and see if I ...
Cort Ammon's user avatar
  • 1,589
39 votes

Why do we still need to know about the Rankine temperature scale?

Rankine is commonly used in the aerospace industry in the United States. Rankine is to Fahrenheit what Kelvin is for Celsius. So when people in the United States were creating programs and using ...
Rick's user avatar
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34 votes
Accepted

A glass of water with ice-cubes in it. Where's the water the coldest; at the top or bottom?

Interesting question! A few things first: As the ice melts, it cools the water around it. Technically, the ice cube melts because the water cools down. This may sound ridiculous at first, but you ...
paracetamol's user avatar
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30 votes
Accepted

There's an absolute zero, is there an "absolute hot"?

In the actual theories of physics the highest temperature which has a physical meaning is the Planck's temperature. $$T_\mathrm{P} = \frac{m_\mathrm{P} c^2}{k} = \sqrt{\frac{\hslash c^5}{G k^2}} \...
ParaH2's user avatar
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30 votes

Why don't room temperature superconductors exist?

The honest answer is we don't know As DrMoishe Pippik points out in their answer we have a good theoretical explanation of superconductivity only for one class of superconductors. And that Nobel Prize ...
matt_black's user avatar
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22 votes

What is the difference between "vapour" and "gas"?

Vapor is a much older word alluding to dampness and it was not coined by scientists. It is in use since the 1300s. The actual meaning of meaning of vapor is "Matter in the form of a steamy or ...
AChem's user avatar
  • 40.9k
20 votes

Why is absolute zero unattainable?

Leaving quantum mechanics aside (it gives me a headache) the second law of thermodynamics prevents absolute zero from being reached in practice. To cool something down, its heat must be transferred ...
Isobutane's user avatar
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20 votes

Is there an uncertainty associated with the value 0 K for absolute zero?

As another answer explains, absolute zero is defined in the Kelvin temperature scale as precisely $\pu{0 K}$. But this is not the entire story, as all measurements have an associated uncertainty (all ...
Buck Thorn's user avatar
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18 votes

Why do we still need to know about the Rankine temperature scale?

Most of us in the world use the Celsius scale to measure temperature for day-to-day purposes. The Kelvin scale has been designed in such a way, it is not only an absolute temperature scale, but also 1°...
Pritt says Reinstate Monica's user avatar
16 votes

Why don't room temperature superconductors exist?

(My answer is a bit off-topic to the theoretical "why" answered well by others, but I believe the particular wording of OP's post is evocative of a relatively common misunderstanding of the ...
DotCounter's user avatar
15 votes

Does motor oil get more viscous when heated & what is the meaning of the SAE motor oil code?

The numbers in the code have nothing to do with viscosity index. However, your understanding of 'W' for winter is correct. The real code for your car is actually SAE 5W-30 where SAE stands for the ...
Mathew Mahindaratne's user avatar
15 votes

What is the difference between "vapour" and "gas"?

The normal use distinguishes "vapour" from permanent gas At normal lab conditions there is a (fairly obvious) distinction between things that could exist as liquids and things where no ...
matt_black's user avatar
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14 votes

Why is absolute zero unattainable?

The usual answer is that it actually is possible because even though the ground state of spacetime itself has non-zero energy, it is not kinetic energy, which is the very definition of temperature. ...
yeoman's user avatar
  • 241
14 votes

There's an absolute zero, is there an "absolute hot"?

It depends on what you mean by ceiling. Are we talking about a practical or theoretical limit? At a high enough energy, the stress-energy tensor will be large enough that you're going to make a black ...
Zhe's user avatar
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14 votes

What exactly is temperature?

Temperature vs kinetic energy [OP:] I've read at many places that temperature is the average kinetic energy of particles present in an object. Temperature has to do with the average kinetic energy ...
Karsten's user avatar
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13 votes

There's an absolute zero, is there an "absolute hot"?

Depends on what you mean by "temperature". In statistical mechanics, a system of interacting parts is in thermal equilibrium if the probability of finding a given part in a state with energy $E$ is ...
hmakholm left over Monica's user avatar
13 votes

What exactly is temperature?

Heat is the transfer of energy to or from the body in forms other than matter flow or work (organized energy transfer, such as pushing). Temperature is only a well-defined property for a collective ...
jezzo's user avatar
  • 1,560
13 votes

Why don't room temperature superconductors exist?

For classical superconductivity, the Bardeen–Cooper–Schrieffer (BCS) theory states electrons travel in Cooper pairs. Since, at the quantum level, it is hard to distinguish one electron from the other, ...
DrMoishe Pippik's user avatar
12 votes
Accepted

Prove that a 10-Degree Temperature Increase Doubles the Rate Constant (k), when the Activation Energy is Approximately 50 kJ/mol

Your method and your mathematics seem perfectly fine, and your calculated result is correct. You are also quite correct that the result will change depending on the value of $E_\mathrm a$ that you ...
hBy2Py's user avatar
  • 17.4k
12 votes

A glass of water with ice-cubes in it. Where's the water the coldest; at the top or bottom?

The convection to produce uniformity depends on a number of nebulous factors: How much ice? How tall is the glass? Diameter of the glass? Is the "glass" really a glass or paper cup, styrofoam cup, ...
MaxW's user avatar
  • 22.3k
12 votes

Why do we still need to know about the Rankine temperature scale?

I am currently studying mechanical engineering in the US, and I have used Rankine. It is used similarly to Kelvin. For example, in my thermodynamics class we used it to analyze various heat engines. ...
BillThePlatypus's user avatar
11 votes
Accepted

Are complex ions thermochromic?

Indeed, this effect is observed in certain select cases. The effect of spin-spin cross over has been mentioned in this regard. There can be some other effects at play, namely: phase transitions, ...
getafix's user avatar
  • 8,495
11 votes

Why is absolute zero unattainable?

Absolute zero can definitely exists (see the later edit), and there is at least one theory, that says that absolute zero will kind of be the norm in the universe at one point. Absolute zero cannot be ...
Andrei's user avatar
  • 211
11 votes

What is the difference between "vapour" and "gas"?

I'm surprised the OED has such a strict definition for gas. I could not find a strict definition in the IUPAC color books (certainly not in the gold book). Presumably these words are in such common ...
Buck Thorn's user avatar
  • 22.1k
10 votes

Why is absolute zero unattainable?

Absolute zero is unattainable. You could do it in theory according to classical laws of physics, but it's quantum mechanics (including quantum electrodynamics) which prevents absolute zero to be ...
MariusM's user avatar
  • 201
10 votes
Accepted

Why there is no temperature scale tied to normal human body temperature?

Why nobody used human body normal temperature as 0? That has been done. See Medical Thermometry and Human Temperature at page 12: 37° Centigrade scale 29.6° Reaumur 98.6° Fahrenheit 77° Walferdin's ...
DavePhD's user avatar
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10 votes
Accepted

Why do we use Δ to mean heating?

The retrieval of this symbol history poses a considerable challenge, as it is scarcely mentioned in textbooks, Google Books and Google Scholar. The current application of the triangle symbol, distinct ...
AChem's user avatar
  • 40.9k

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