Questions tagged [physical-chemistry]

The study of chemical systems using the laws and concepts of physics. This usually requires the techniques of thermodynamics, statistical mechanics and quantum mechanics.

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Deliquescence/efflorescence: How can I convert between salt concentration and RH?

I am looking at two phase diagrams, one has axes of $T$ and $\%\ce{MgClO4}$ in a $\ce{H2O-MgClO4}$ mix, and the other has axes of $T$ and relative humidity. The authors of the second phase diagram say ...
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12 votes
5 answers
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Why does oxygen not condense onto open dewers of liquid nitrogen?

I had a discussion with my supervisor today after I was a touch careless pumping down a flask with a liquid nitrogen cold trap attached. I checked, and there are reports of explosions after running ...
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7 votes
1 answer
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Where can I obtain tables of P-V-T/compression factor data?

Some recent research I'm dealing with has required me to look for tables of experimental pressure/volume/temperature values (equivalently, a table of compressibility/compression factors in terms of ...
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23 votes
3 answers
541 views

Energy-efficiency aside, what are the chemical constraints on CO₂ capture and methanation?

Synthesising $\ce {CH4}$ from air and water (in a non-biological process) has been proposed as one form of energy storage. What are the chemical constraints at play here? That is to say, what sort of ...
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7 votes
1 answer
360 views

Negative retention for chloride in hydrolysate filtration

I tried to fractionate proteins as a function of their size with an ultrafiltration membrane. I observed a higher concentration of chloride in my permeate than in my feed or retentate. The proteins do ...
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27 votes
2 answers
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What is antisymmetric exchange? What is J-strain? Where does it come from?

I'm reading a paper1 by Sanakis, et al. that characterises the magnetic coupling in the $\ce{Fe3S4}$ clusters present in bacterial ferredoxin II and beef heart aconitase as arising through something ...
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8 votes
1 answer
1k views

How to calculate the equilibration time of two connected chambers of salt solution, initially at different concentrations?

I am trying to build a system of two connected chambers, one of which is also connected to a cuvette, so I can perform a spectrometry experiment with different concentrations of $\ce{KNO3}$ solution. ...
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21 votes
2 answers
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What is a rigorous definition of gas volume, and how is the Van der Waals equation derived?

I am confused about the justification for the corrections to the ideal gas law in the Van der Waals equation: $$p=\frac{nRT}{V-nb}-a\left(\frac{n}{V}\right)^2$$ I understand that the equation ...
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7 votes
1 answer
5k views

Hanging a spoon on the face

Well, I have seen many comical acts where people balance a spoon (or a fork) on different parts of the face like on the tip of the nose, forehead etc. The do this by blowing moist air (see below) and ...
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19 votes
3 answers
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Choice of doping elements in semiconductors

In a typical semiconducting material, we start with silicon (group IV) and introduce atoms of group V or group III depending on whether we are constructing an n- or p-type semiconductor respectively. ...
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10 votes
2 answers
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How does dimethylsulfoxide serve as a cryoprotectant?

In cell culture, dimethylsulfoxide (DMSO) is added to prevent the formation of ice crystals which may lyse the cells. Exactly how does dimethylsulfoxide act as a cryoprotectant?
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179 votes
8 answers
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Can an atom have more than 8 valence electrons? If not, why is 8 the limit?

According to some chemistry textbooks, the maximum number of valence electrons for an atom is 8, but the reason for this is not explained. So, can an atom have more than 8 valence electrons? If ...
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15 votes
1 answer
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Are there any examples of nuclear spin isomers having consequences for chemical reactivity?

Ortho- and parahydrogen are two forms of the $\ce{H2}$ molecule that are distinguished by their pairing or antipairing of nuclear spins, giving rise to metastable singlet (ortho-) and triplet (para-) ...
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23 votes
4 answers
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what kind of suspension liquid should be used with ferrofluid (so it does not stain the glass)

Please take a look at the following video: I am working on a new project, and I need to find whats the best liquid to hold ferrofluid inside the glass (or maybe even plastic) container, so that ...
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11 votes
1 answer
4k views

What's the difference between precipitate and turbidity?

In many tests for various radicals, a "<color> precipitate" or "<color> turbidity" is mentioned. For example, lead ...
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25 votes
6 answers
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Why are equations of state for a non-ideal gas so elusive?

The ideal gas equation (daresay "law") is a fascinating combination of the work of dozens of scientists over a long period of time. I encountered Van der Waals interpretation for non-ideal gases ...
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27 votes
3 answers
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Why does ice cream make soda fizz?

I've noticed that adding a chunk of ice cream to soda makes the soda fizz slightly near the soda-ice cream interface. I thought it was a physical effect due to the temperature, but adding ice has no ...
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19 votes
1 answer
829 views

When simulating spectral line broadening, which convolution is preferred?

Many computational chemistry packages permit the calculation of vibrational and electronic spectra. These spectra are obtained as a set of discrete eigenvalues however they are often convolved with ...
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4 votes
1 answer
10k views

Can dissolution reactions be endothermic?

Is it possible for a dissolution reaction of the form $$\ce{X(s) ->[solvent] X (solv)}$$ or $$\ce{M_mX_x (s) ->[solvent] m M^x+ (solv) + x X^m- (solv)}$$ to be endothermic, i.e. $\Delta_\...
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10 votes
2 answers
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Gas chromatography/mass spectrometry: Can I use peak ratios and molecular mass to derive quantity?

Can derive the quantity of a substance from a GC/MS report if I know: the ratio to another substance in the data, the quantity of that second substance, and the molecular mass of both substances. ...
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16 votes
1 answer
433 views

How does conductivity work for non-redoxed ions?

Related (very similar, but here I want a mechanism) https://physics.stackexchange.com/q/21827/7433 By the Kohlrausch law, all ions contribute to the conductivity of an electrolyte. Now, as I ...
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12 votes
2 answers
18k views

What are the major factors that influence LogP

The partition coefficient is a very useful metric in characterizing compounds particularly drugs. What chemical properties influence that partitioning? Are chemical moieties additive in their LogP? ...
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9 votes
6 answers
4k views

A quick method for separating liquids?

I'm looking for a way to take 3 separate liquids (liquids which function as paint -- they will all be different colors), put them together into a container, and then rapidly separate them back to ...
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14 votes
4 answers
75k views

General rules for deciding volatility

Given an organic compound, is there any way to decide if it is volatile (or compare volatility--everything is volatile in the end)? Volatility is due to the tendency to evaporate. The conclusion I ...
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23 votes
3 answers
16k views

Why is distillation not a viable way to separate ammonia from water?

Since the steam pressure of ammonia is higher than that of water, I would expect distillation to be a reasonable way of separating a mixture of both. However, in industrial applications known to me ...
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