Questions tagged [temperature]

A measure of the average kinetic energy of the particles in a sample of matter; may be expressed either in kelvin (symbol K) or in degree Celsius (symbol °C).

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94
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Why is absolute zero unattainable?

We were dealing with the Third Law of Thermodynamics in class, and my teacher mentioned something that we found quite fascinating: It is physically impossible to attain a temperature of zero ...
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A glass of water with ice-cubes in it. Where's the water the coldest; at the top or bottom?

Suppose that I fill a glass with ice water. As the ice melts, it cools the water around it. Given that cold water is denser than hot water, I would presume that the cold water would sink to the ...
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There's an absolute zero, is there an “absolute hot”?

This might be more of a physics question, but is there a ceiling on how hot things can get? What happens at this temperature?
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Why do we still need to know about the Rankine temperature scale?

I am learning process principles in chemical engineering and I was taught various temperature units like Fahrenheit, Celsius, Kelvin, and Rankine. I see the first three being used quite commonly, but ...
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When can a molecule be considered freely rotating at room temperature?

This question sparked from a long discussion in chat about the nature of $\ce{H2O2}$ and whether that molecule can be considered to rotate around the $\ce{O-O}$ axis (and hence display axial chirality)...
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Why is −78 °C a magic temperature for organic reactions?

In many organic reactions that I have seen, running the reaction at $\mathrm{-78\ ^\circ C}$ seems to be quite a popular choice, but I've never seen any explanation for this. What makes this ...
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Why does water evaporate at room temperature?

When water temperature reaches $100\ ^\circ \mathrm{C}$, the molecules get so excited that the hydrogen atoms lose the bonds to the oxygen atom and therefore the water starts to become gas. I get that,...
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Does the Maxwell-Boltzmann distribution apply to gases only?

The Maxwell-Boltzmann distribution can be used to determine the fraction of particles with sufficient energy to react. I know that the curve applies to gaseous reactants and would like to know whether ...
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Is there an uncertainty associated with the value 0 K for absolute zero?

When I say absolute zero, I’m not talking about the hypothetical temperature 0 K; I’m talking about the temperature at which a thermodynamic system has the lowest energy. Everywhere I look, sites ...
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Why is the Haber process carried out at such high temperatures?

On a large scale, ammonia is prepared via the Haber process: $$\ce{N2(g) + 3H2(g)->2NH3(g)} \qquad \Delta _\mathrm{f}H^\circ = -46.1~\mathrm{kJ \cdot mol^{-1}}$$ The optimum conditions for the ...
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Why do helium balloons expand in volume as they go higher?

I realize as balloons go higher, the atmospheric pressure decreases, doing less to counteract the force of the gas particles pushing against the inner walls of the balloon. But at the same time, doesn'...
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Why no thermal expansion for camping tents?

I know that solid materials expand when heated, which is called thermal expansion. But what is happening to tent square or tent canvas of (plastic?) camping tents? I have noticed, that during the day,...
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Are complex ions thermochromic?

Does raising the temperature of a complex ion (formed from a transition metal ion and ligand(s)) affect its color? For example, if the temperature of $\ce{[Cr(H2O)6]^3+}$ is raised, will its color ...
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Negative Kelvin Temperature

I remember my Physical Chemistry Professor saying that very tiny negative Kelvin temperatures have been achieved on the quantum level. Is this true?
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What is the reason for anomalous expansion of water?

What is the reason for anomalous expansion of water? Why doesn’t it simply expand on heating or contract on cooling? Why it shows anomalous behavior at 4 degrees Celsius? Why not on 4.6 or 10 (or ...
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Do all gases occupy same volume at equal temperature and pressure conditions?

Why does one mole of all gases occupy 22.4 L at standard temperature and pressure? According to my thinking, it may be due to equal diffusion of all particles when at a particular temperature and ...
10
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1answer
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Thermochromism in PbI2

I noticed while heating some PbI2 powder that it reversibly changes from a yellow to a dark red. However, I was unable to find anything on this thermochromism. There are related cases in TlI and AgI ...
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Is there a structured data source containing information on the World Health Organisation's Stability Testing Policies?

Hoping to automate some product testing guidance software, I've been attempting to find a (hopefully live, up-to-date) Database, Web-service, or other structured data source containing the ...
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Can paper burn without oxygen or air?

If you put a paper inside an oven vacuum packed and go beyond $250~\mathrm{^\circ C}$, will it burn? There's no oxidizer. If not, what will happen?
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Why does the distance between molecules increase when the temperature is raised?

I have learnt that when we heat ice-like substances it changes to water and when I asked my teacher she said that the distance between molecules increases. When I thought about it a bit more a ...
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How to determine omitted units in a publication

I have found a 1954 paper in J. Am. Chem. Soc. which gives various temperatures in degrees but does not specify units. A snippet of the introduction is: Titanium reacts appreciably with fluorine ...
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What is the significance of 273.16 K?

Today, at my chemistry class, we were learning how to convert Celsius to Kelvin with exact values. I said we add 273.15 K to given Celsius but my colleague said we add 273.16 K. Yes, I did check on ...
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How is Negative Temperature Hotter than Infinite Temperature?

Recently I have read articles stating that negative Kelvin has been achieved. I was a bit speculative at first as I though how can you get cold than 0 Kelvin, but after doing some research it makes ...
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Temperature of an atom

I read somewhere that the temperature of an atom is not defined. The definition of temperature is only for larger systems. Why is this so?
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Is there any scenario in which the size of a molecule increases due to an increase in temperature?

Take an ice cube for example. Heat is applied in a closed container until it is vaporized completely. Will the molecule's size be larger (on average)? Is there a substance that you know of that has ...
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How are hot and cold defined?

My teacher asked me this question a few days ago. "How to define hot and cold?" And I said, "The higher the temperature, the hotter you are. The lower the temperature the colder you are." But my ...
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What causes the colour when conducting flame tests on solid salts?

The normal technique for flame tests is to dip a clean nichrome or platinum wire into a solution of the relevant salt, and observe the resulting flame colour when inserting the wire into a non-...
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What determines humidity limit / dew point of the air? - Why can air only hold a certain amount of water?

From Wikipedia: The dew point is the temperature at which the water vapor in a sample of air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates. At ...
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What are the degrees of freedom that define the temperature of an ionic solid (such as sodium azide)?

Degrees of freedom describe the different ways atoms move in a sample. For a pure ideal gas made of non-linear molecules, there are 3N degrees of freedom (N is the number of atoms in the molecule), 3N-...
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What is the difference between temperature and thermodynamic temperature?

My course book says that kelvin is the unit of thermodynamic temperature, then what is the difference between temperature and thermodynamic temperature.
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Does cooling a potato change the nature of its carbohydrates?

A talk-show guest of Joe Rogan claimed that cooling a potato after cooking creates "resistant starch" that's better for human consumption https://www.youtube.com/watch?v=niwqfwA2Lb8 The claim is ...
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Why is bread warm at room temperature?

If I buy a loaf of freshly-made bread and leave it out at room temperature for a day or two, when I reach into the bag the air inside is much warmer than the rest of the room. Why?
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Why does heating transform the aquacomples of slightly acidified cobalt(II) chloride solution to the chlorido complex?

There is a famous demonstration where, if you mix a $\ce{CoCl2}$-solution with the right amount of $\ce{HCl}$ you will end up with the pink $\ce{[Co(H2O)6]^2+}$ complex but when heating it to boiling ...
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What could cause a peak to split into 2 resonances as temperature increases in NMR spectroscopy

I understand that some peaks may coalesce upon an increase in temperature due to an increase in free rotation, this does occur with some peaks in my data. Why might you see a peak split into two other ...
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Is there a chemical reaction that speeds up when the temprature gets lower?

We were talking about chemical reaction speed on our chemistry class, and I asked my teacher if there is a chemical reaction that speeds up when the temprature gets lower? I think this is not everyday ...
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How to calculate percent error for absolute zero?

In chemistry lab, we did an experiment with water of various temperatures to extrapolate a value for absolute zero based on experimental pressure values for water at different temperatures. Naturally, ...
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What is an example of a very low temperature endothermic reaction?

Shakashiri describes the reaction of solid Ammonium Thiocyanate and solid Barium Hydroxide Octahydrate resulting in an endothermic reaction leading to subzero temperatures. I've performed this ...
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Temperatures Below Absolute Zero [closed]

This seems like a farce... Quantum gas goes below absolute zero Ultracold atoms pave way for negative-Kelvin materials. by Zeeya Merali, Nature News 03 January 2013, DOI: 10.1038/nature.2013....
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Are there two compound resins that tolerate over 1000°C for glass/carbon fiber?

I'm a hobby enthusiast that loves to play with electronics so my major is not in chemistry, there for I'm hoping that this forum is the right place to find aid in this question. I've searched day in ...
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1answer
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What is the proper term for lines of constant volume and constant enthalpy on a thermodynamic diagram?

I know an isotherm is a line of constant temperature. Isobar is a constant pressure line. Isentrope is a line of constant entropy. But what do you call a line of constant volume? An Isochore? And ...
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Thermometer fluid is separated, defective?

I bought a thermometer from Cole-Parmer having kerosene as the fluid, and the fluid is broken up. The fluid in the bottom part goes up to about 10 °C even though it is 20 °C in the room, then there is ...
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Determining weight-percent methanol in water from specific gravity and temperature

The company I'm working with uses a fuel mixture of methanol and water. We use a hydrometer to measure specific gravity, in order to test the composition of fuel received from our suppliers. To ...
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1answer
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Is change of pH of water with respect to temperature linear?

Only recently I learned that the pH of water varies with temperature, from about 7.47 at 0 °C to 6.14 at 100 °C. My question is, first, is there a geometric explanation for this, in the sense that ...
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Why is the yield of substitution reactions decreased at higher temperatures?

This is according to my text : Increasing temperature favours elimination over substitution. This is because energy of activation for elimination is higher than that of substitution since higher ...
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Super-cooled liquids

I understand that it is possible to cool a liquid past its freezing point, and still maintain its liquid state because crystallisation would not happen in the absence of a seed crystal. My question, ...
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Is it possible to freeze water by dissolving a salt?

Theoretically, by dissolving a salt in water the melting point lowers, approximately 1.86 K kg/mol, making it more difficult to freeze water. However, the process of dissolution of certain salts is ...
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Peak Wavelength of Emission Spectrum of a Flame vs. Actual Flame Temperature

I am looking at a lab test of two variants of mixed hydrocarbon gas (57.8% $H_2$, 16.9% $N_2$, 12.4% $CH_4$, 1.11% water vapor, and 11.8% "unknown" gases) burning in oxygen which shows a discontinous ...
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What are the physical properties affected in ZnO when there is a sulfur impurity?

I have a question. I work at a brass metal foundry where one of our waste products is $\ce{ZnO}$, which we sell. Because we have been making new alloys which contain sulfur, our $\ce{ZnO}$ has a very ...
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How can I reduce Crystallization temperature of seed oil to be used in winter as biodiesel?

How can I reduce Crystallisation temperature of seed oil to be used in winter as biodiesel? The glycerol has been removed from the oil, and white spirit is used to reduce its viscosity.
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How would you measure the rate of this SN1 reaction?

I am performing the following $\mathrm{S_N1}$ reaction: $$\ce{t-BuOH + HCl -> t-BuCl + H2O}$$ I would also like to measure the rate of this reaction, but I cannot seem to find a way. I initially ...