47
votes
Accepted
Is there a cheap, safe liquid that evaporates EXOthermically around room temperature?
No such liquid, safe or otherwise, can exist. Evaporation is a strictly endothermic process in all cases.
The change in state from liquid to gas is marked by the individual particles gaining enough ...
- 17.2k
40
votes
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What properties of carbon dioxide make it a greenhouse gas?
According to the Intergovernmental Panel on Climate Change (IPCC):
"Greenhouse gases are those that absorb and emit infrared radiation in the wavelength range emitted by Earth."
In order for a ...
- 17.3k
38
votes
Can thermite be lit while mixed into butane? If not is there a flammable liquid that would work?
Thermite is a solid-solid reaction that I think would be greatly inhibited by any sort of intermediate. In either case, the smoke, the dust and the copious amounts of nitrous oxides produced will not ...
- 2,737
33
votes
Accepted
When a candle burns, why does the top of wick glow if bottom of flame is hottest?
The wick temperature does not have to be the same as the flame temperature.The flame is hottest at the bottom, but the wick is hottest at the top.
For a candle, the wick burning isn't the intended ...
- 12.3k
29
votes
Microwaving a glass of water, what happens?
Heating water on a hot plate is safe, because the hottest point is at the bottom of the pot. A lot of relatively small bubbles appear there without much overheating of the water, because there is a ...
- 11.9k
29
votes
When a candle burns, why does the top of wick glow if bottom of flame is hottest?
Because fire is not the same thing as light.
Michael Faraday did a wonderful job of explaining how the candle works, and I direct you to look at it (there are also Youtube videos giving a modern take ...
- 17.2k
24
votes
Can single molecules of C and O2 react in isolation, and if so how will momentum be conserved?
$\ce{C + O2}$ is awfully complicated, so let's just pretend you've asked this:
In a single act of the reaction $\ce{H. + H .-> H2}$, how is momentum conserved?
That's a legitimate concern all right....
- 30.9k
23
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Can thermite be lit while mixed into butane? If not is there a flammable liquid that would work?
In addition to the points Stian raised, it's important to realize that thermite is very difficult to ignite. The ignition temperature is very, very high, higher than you can easily get by burning ...
- 711
23
votes
Accepted
How can a thermometer ever show the actual temperature of an object if the object loses heat to the thermometer?
I'll start by mentioning that there's no such thing as an exact measurement—there is always some measurement error. The only observations that can be numerically exact are counted numbers of discrete ...
- 12k
22
votes
Accepted
Burns from boiling water and steam
Let’s consider the following cases:
getting $1\,\mathrm{mol}$ of $100\,\mathrm{°C}$ water on one’s skin
getting $1\,\mathrm{mol}$ of $100\,\mathrm{°C}$ air on one’s skin
getting $1\,\mathrm{mol}$ of $...
- 66.9k
22
votes
Accepted
Can carbon dioxide be reduced to carbon monoxide and oxygen to produce energy?
Unfortunately, the question as stated is thermodynamically impossible. Let's look at the proposed reaction:
$$\ce{CO2(g) -> CO(g) + O(g)}$$
This reaction is simply a bond dissociation (specifically,...
21
votes
What properties of carbon dioxide make it a greenhouse gas?
When heat is leaving earth it leaves as infrared radiation. Greenhouse gases are gases that are able to absorb this infrared radiation. If we look at the infrared emission spectrum from Earth[1]:
We ...
- 2,142
19
votes
Accepted
How to evaluate the heat of formation with computational chemistry?
Your approach is quite correct, but as Jan already pointed out, it is incomplete. What you calculated is the difference in the electronic energy of the reaction $$\ce{H2 (g) + 1/2 O2 (g,\,{}^1\Delta_{...
- 43.7k
19
votes
Accepted
If aliens lived in a hydrogen (or any flammable gas) based atmosphere, would they perceive oxygen to be flammable?
Absolutely yes.
Lighting a torch in such an environment would simply be the reverse physical process (and same chemical process) of what is done in our oxygen-containing atmosphere. In the chamber ...
- 17.3k
19
votes
Accepted
Does all fire only emit light on its outermost shell?
The answer is NO.
The article you quote makes a completely unwarranted generalisation that "all flames are hollow". This is true of some flames but only because the fuel that is burning is ...
- 35.1k
18
votes
Relation between constant-pressure and constant-volume heat capacities: Cp - Cv = nR
Preliminaries
Consider $U = U(V,T, p)$. However, assuming that it is possible to write an equation of state of the form $p = f(V,T)$, I don't have to explicitly address the $p$ dependence of $U$, ...
- 8,425
17
votes
Accepted
Strong exothermic mixing of two 'safe' liquids
If you need a quick source of moderate heat, why not use a single liquid? Sodium acetate trihydrate ($\ce{CH3COONa·3H2O}$), for example, releases heat energy on crystallization... and it takes very ...
- 29.6k
16
votes
Accepted
Relation between constant-pressure and constant-volume heat capacities: Cp - Cv = nR
The heat capacities are defined as
$$C_p = \left(\frac{\partial H}{\partial T}\right)_{\!p} \qquad \qquad C_V = \left(\frac{\partial U}{\partial T}\right)_{\!V} \tag{1}$$
and since $H = U + pV$, we ...
- 70.8k
15
votes
Microwaving a glass of water, what happens?
The mode of heating of a water glass in a microwave and on a stove is actually very similar. While it's true that microwave radiation penetrates somewhat into the body of water, the penetration depth ...
- 505
14
votes
What is the difference between enthalpy (H) and heat (q)?
Enthalpy and heat are entirely different things.
Enthalpy is a function of state. If you know the state of a system, you know its enthalpy. If you know the starting and ending states of a process, ...
- 283
14
votes
Can thermite be lit while mixed into butane? If not is there a flammable liquid that would work?
I'm not at all sure that termite is a useful solution to this problem. The thermite reaction takes place between iron oxide and aluminium, producing a lot of heat and molten iron as a result. This ...
- 361
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 ...
- 37.9k
14
votes
Accepted
What factors promote honey's crystallisation?
The decisive factor is the plant origin of honey. The major components ( reportedly by some beekeeper books of my passed away father ) have ratio glucose : fructose about 1:1 to 1:1.7. Glucose ...
- 37.8k
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 ...
- 1,540
11
votes
Accepted
What temperature is required to burn pencil lead graphite?
You have two problems.
1.) pencil lead graphite is actually a graphite-clay composite.
2.) carbon does not sustain burning easily unless it is held at very high temperatures.
Pencil lead will not ...
- 12.3k
11
votes
Accepted
How does sulfuric acid react to heating?
Sulfuric acid, $\ce{H2SO4}$, having an enthalpy of formation of $-814\ \mathrm{kJ/mol}$, is quite stable and won't decompose easily.
According to A Kinetic Study of the Decomposition of Spent Sulfuric ...
- 4,985
11
votes
Can thermite be lit while mixed into butane? If not is there a flammable liquid that would work?
This will not answer the part of igniting thermite, but addresses the issue of the snow on the driveway, that you want to forget.
Instead of heating from top (by a torch), you may consider heating ...
- 27.7k
11
votes
Accepted
Why would a ~1 cm thick layer of argon be a significantly poorer conductor of heat than air?
The thermal conductivity coefficients of some gasses in units of W/(m•K) are helium 0.142, argon 0.016, air 0.026, methane 0.03, propane 0.015, bromine 0.004, and steam 0.018. These are all rather ...
- 29.8k
10
votes
How to evaluate the heat of formation with computational chemistry?
you need to perform a Hessian calculation and add the enthalpy correction to each energy
what spin state are you using for $\ce{O2}$?
HF/6-31G(d) is probably not good enough for geometries and ...
- 4,789
10
votes
Can carbon dioxide be reduced to carbon monoxide and oxygen to produce energy?
You’re looking at bond dissociation energies. They, however, do not give a good picture. A better place to start looking is the standard enthalpy of formation. The linked Wikipedia article provides an ...
- 66.9k
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