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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].

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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 ...
29
votes
3answers
4k views

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?
24
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5answers
14k views

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 ...
22
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4answers
895 views

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?
21
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1answer
2k views

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 ...
20
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3answers
5k views

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 ...
17
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2answers
28k views

Why does diamond conduct heat better than graphite?

We were made to accept by our teachers (without any explanation) that diamond conducts heat better than graphite. What is the reason behind this behaviour of diamond.
16
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3answers
2k views

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) -> ...
15
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9answers
8k views

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 ...
14
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6answers
5k views

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 ...
14
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2answers
142k views

What is “heating under reflux”?

When dealing with organic reactions, heating under reflux is often required, such as the oxidation of Toluene using acidified $\ce{KMnO4}$ and dilute $\ce{H2SO4}$ to Benzoic acid($\ce{C6H6O2})$ What ...
13
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2answers
5k views

Burns from boiling water and steam

Why is a burn to the skin caused by steam more serious than a burn caused by the same amount of boiling water at the same temperature? The temperature is the same, which implies that the kinetic ...
13
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1answer
700 views

How is enthalpy change equal to heat supplied at constant volume?

We know that: $$\begin{align} H &= U + pV \\ \Delta H &= \Delta U + \Delta (pV) \end{align}$$ Now, If $p$ is constant, $$\begin{align} \Delta H &= \Delta U + p\Delta V \\ &= q_p + ...
12
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3answers
37k views

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.
11
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1answer
1k views

Why would a ~1 cm thick layer of argon be a significantly poorer conductor of heat than air?

In yesterday's new Periodic Video, Argon (new) - Periodic Table of Videos, after about 07 min 00 sec, Sir Martyn Poliakoff says: The final, and I have to admit perhaps slightly boring application ...
10
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3answers
15k views

Relation between constant-pressure and constant-volume heat capacities: Cp - Cv = nR

For an ideal gas, we have $$C_p - C_V = nR$$ where $C_p$ is heat capacity at constant pressure, $C_V$ is heat capacity at constant volume, $n$ is amount of substance, and $R=8.3144598(48)\ \mathrm{J\...
10
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2answers
32k views

Heats of combustion and stability of rings

Can anyone explain why? If you think about it, without having the data of the heat of combustion of each type of bond, you can't really answer this question. I know that cyclopropane has a higher ...
10
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1answer
1k views

What chemicals are used in receipt paper?

Most "invisible inks" turn brown when heated and they take a while to transform. I would like to make (or obtain) an "ink" that responds to the heat of an iron and permanently turns black or a ...
9
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5answers
35k views

Why is it obligatory to cool down the container of a sample to measure its mass in a lab?

We were doing an experiment about hydrated crystals and more precisely how to determine $n$ in $\ce{CuSO4.nH2O}$. After we heated the crucible we were to cool it down using a Desiccator. Then this ...
9
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3answers
2k views

Which materials/compounds expand in response to cold temperatures?

Which materials or compounds expand in response to cold temperatures? This material or compound should expand at a slow (but constant rate), from about 0–20 months when in the following temperature ...
9
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2answers
36k views

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

Which of the following must be true for adiabatic processes? $C_\mathrm{V} = C_\mathrm{p}$ $\Delta H = 0$ $\Delta U = 0$ $\Delta S = 0$ $q = 0$ (Source: Chemistry GRE) The answer ...
9
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2answers
22k views

How much does water expand when heated, and does salt affect that?

For this question, assume all things not mentioned are perfectly controlled, all at 14.7lbs of atmospheric pressure, and water is 100% pure of anything not mentioned, with no dissolved air. Given a ...
9
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2answers
14k views

What is the difference between tempering and hardening metals and their end products?

I think I've heard hardening is when you dunk red-hot metal into cold water, and tempering is when you take that hardened metal, heat it slightly, and then let it cool slowly. However what is the ...
9
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1answer
495 views

Why does a glass tube show white bands after being heated with a torch?

When I use a torch to split a glass tube, there's always a hazy white band which appears. Does anyone know what the cause of this is? It was a hydrogen-oxygen torch. The glass is fused quartz glass, ...
8
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3answers
7k views

Can you heat water with additives?

I have been curious about this question for a while. If you want to warm up a large amount of water, is it feasible to do this by adding a substance that has an exothermic reaction with the water? ...
8
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2answers
8k views

How does sulfuric acid react to heating?

How would $\ce{H2SO4}$ react to heat ? I assume that it would form toxic sulfur (di/tri)oxide, but I can't find any information on this. I'm concerned about fire hazards specifically, so assume very ...
8
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3answers
8k views

Chemical reactions with a room-scale cooling effect

Are there chemical reactions that could cool down an average sized room by a noticeable amount (say 5 °C)? I would like to investigate if it is possible to have a situation where I can mix 2 ...
8
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3answers
7k views

What happens if you autoclave HEPES?

Many molecular biology protocols advice against sterilizing HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) solutions by autoclave. Supposedly, HEPES is heat labile, and the high ...
8
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1answer
4k views

How to calculate the heat released when sodium hydroxide is dissolved in hydrochloric acid solution?

How to calculate the heat released when sodium hydroxide is dissolved in hydrochloric acid solution? Here is the data I gathered from a lab experiment: $50\ \mathrm{mL}$ of hydrochloric acid solution ...
8
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2answers
339 views

Silicone for use in casting Bismuth

I am trying to cast bismuth, which melts at 271.4 °C. Silicone rubber seemed like a good material to use for a mold, given its flexibility and the ease with which it can be cast itself, as well as its ...
7
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4answers
56k views

How do I chill water without a refrigerator?

How can we chill water in a plastic bottle without a freezer or refrigerator? Scenario: I'm in the office and I have two plastic bottles of water (brought from home). I'm in the office for 3 to 4 ...
7
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2answers
20k views

What is the difference between enthalpy (H) and heat (q)?

It seems that in some cases it's the same (that is, $\Delta Q_p=\Delta H$) yet in others they differ. For example, \begin{align} \ce{2H2(g) + O2(g) &->2H2O(l)} & \Delta H &= -572~\...
7
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1answer
19k views

Why does a substance with an endothermic heat of solution dissolve?

How does a substance with an endothermic heat of solution dissolve?
7
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1answer
882 views

Why does lead nitrate powder on heating starts turning yellow from the top rather than from the bottom?

Today while in school, I observed the thermal decomposition of lead nitrate. The peculiar thing I noticed was that the lead nitrate powder in the test tube starts turning yellow (due to the formation ...
7
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1answer
995 views

How to calculate the mass of iron with a temperature of 325 °C needed to melt ice and raise the temperature of water from 0 to 22 °C?

A large well-insulated container holds a mixture of $75\ \mathrm g$ of ice and $100\ \mathrm g$ of water at $0\ \mathrm{^\circ C}$. Using the data given below, calculate the mass in grams of solid ...
7
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1answer
665 views

What happens if I make a hole in a container with superheated water?

Superheated water is achieved by heating water above 100 degree Celsius under high pressure. Now, suppose the temperature at which the water is getting heated is around 250 Celsius and sufficient ...
7
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1answer
178 views

Can water be ignited in an ozone atmosphere?

According to my calculations, the reaction $\ce{H2O + O3 -> H2O2 + O2}$ should be favourable under standard conditions. However, I am told that the reaction is probably very slow in solution since ...
7
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2answers
3k views

Does sodium produce water when it reacts with water?

My 10th grade chemistry book states that: "Metals react with water and produce a metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it to further form metal hydroxide. ...
6
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3answers
17k views

Why won't water freeze if you put ice in it, despite ice being frozen?

Just now I got some room temperature water and added some ice to cool it, and it just came to me, like the scientist I wish I was ... why doesn't frozen (freezing point) ice added to higher ...
6
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2answers
10k views

Why is a tin can that appears like galvanised steel rusting?

I bought a canned pineapple and finished the content. The part of the can that is in contact with the liquid appears like galvanized steel (crystalline surface or spangles sort of appearance), while ...
6
votes
1answer
2k views

Why is the Dulong–Petit law not applicable to the elements Be, B, C, or Si?

According to the Dulong–Petit law, the molar heat capacity of a solid element is approximately $3R$ (where $R$ is the gas constant $\pu{8.314 J K-1 mol-1}$.) This is useful for calculating the atomic ...
6
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1answer
90 views

Is there a heat capacity of an object when it is melting?

Is there a heat capacity of an object when it is melting? I’m questioning it since the temperature doesn’t change during phase transitions and the unit of heat capacity is joule per kelvin.
6
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1answer
11k views

Difference between Superheated steam and Superheated water?

I'm working on a project (school level) and in it I'll be dealing with the pressure generated by water when superheated. I could understand the concept of superheated water but superheated steam is ...
6
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2answers
5k views

How can I measure the internal temperature of a solid metal?

I’m heating up several metal blocks as part of an experiment to determine their specific heat capacities. In a nutshell, I’m heating the blocks of known mass to 100 °C, then adding them to an ...
6
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1answer
148 views

Do I understand why heat capacity is called 'heat *capacity*'?

The notion of heat capacity seemed a little odd to me. I thought that the word 'capacity' could be throwing me off. Do I understand the notion correctly? I take the word 'capacity' to express, ...
6
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1answer
121 views

Are wrinkles\folds in paper reversible by heat, pressure or something else?

I ran into this question on Lifehacks.SE, regarding how to remove wrinkles from a crumpled piece of paper. Suggestions included ironing the paper or placing it under some heavy books for a few days. ...
6
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1answer
517 views

How is work converted to heat?

My book says work can be converted into heat but I want to know how work affects kinetic energy of molecules which, when transferred, is called heat?
6
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0answers
123 views

Computational heat of reation vs. using literature values

My question is I don't understand how to explain why or what I did wrong to have such large differences between my computational heat of reaction and heat of reaction using enthalpies of formation ...
6
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0answers
101 views

Seeking titanium compound, melting point <1600 °C, decomposes to TiO

The title says it all. I’m new to glass making, and I need a titanium compound that will render me $\ce{TiO}$ through decomposition, and has a melting point under 1600 °C. Hopefully I can get one ...
6
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0answers
102 views

Scission of carbon dioxide bonds using electric arc [duplicate]

I've done my research on this so I've seen the questions asking about the same premise without using plants. Basically, this is a thought experiment I came up with. Whether or not I perform it ...