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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11
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3answers
4k 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 ...
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1answer
137 views

What is in silico energy optimization?

While doing computational chemistry for both organic and inorganic compounds, an energy optimization of that compound is done before starting a study. For example, if we do drug docking studies using ...
11
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1answer
469 views

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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1answer
1k views

Why can dissolution reactions (e.g. dissolution of calcium chloride) be exothermic?

Dissolution reactions are normally endothermic, and crystallization reactions are normally exothermic, but there are some exceptions -- such as the dissolution of calcium chloride. Why is this so?
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1answer
578 views

Writing the chemical equation given molarity

If I am given the molarity of two substances and I know how they react, how can I write the balanced chemical reaction? i.e. experimentally I found: $\pu{1.0 M}$ $\ce{NH_3(aq)}$ mixed with $\pu{0.1 M}...
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3answers
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Does potential difference or current drive electrolysis?

Would a high voltage ( of the order of a few score kV ) drive electrolysis? Or, does it require a large current and low voltage? Alternatively, does electrolysis require both large voltage & ...
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1answer
288 views

What undergoes reduction in a zinc-copper voltaic cell?

In a $\pu{Zn-Cu}$ voltaic cell, the electrolyte is sodium chloride solution. The question was: In this cell, which of the following undergoes reduction? My answer was copper, but why is the exact ...
11
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4answers
15k views

Maximum temperature attainable by thermite reaction

In the thermite reaction $$\ce{2Al(s) + Fe2O3(s) -> 2Fe(l) + Al2O3(s)}$$ what is the maximum temperature attainable by the products? Assume reactants at $25\ \mathrm{^\circ C}$ and $1\ \mathrm{...
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2answers
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What is the opposite of a surfactant?

Surfactants decrease surface tension between two fluids. What do you call a substance that increases the surface tension between two fluids? How is this effect acheived?
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0answers
45 views

Compounds that vary water's superheated and supercritical limits [closed]

Are there any compounds that reduce water's sensitivity to extreme heat change and/or volatility to high heat (over 800 degrees Fahrenheit), whether organic or inorganic?
3
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1answer
595 views

What would happen to a Water/Lard Mix under pressure and high heat?

If water is mixed with lard oil and heated (creating some super-critical water), how does this affect the volatility of the mixture in comparison if it is a pure mix of either water, or lard oil? ...
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1answer
3k views

Should I use specific heat to calculate how much fuel is required?

Question: A backpacker wants to carry enough fuel to heat $\pu{3.0 kg}$ of water from $\pu{20 ^\circ C}$ to $\pu{100.0 ^\circ C}$. If the fuel he carries produces $\pu{36 kJ}$ of heat per gram when ...
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1answer
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Which element is being reduced in this reaction?

Which element is reduced in this reaction: $$\ce{2KMnO_4 +3NaSO_3 +H_2O ->2MnO_2 +3NaSO_4 +2KOH}$$ I am trying to figure out which elements lose their electrons, but how am I supposed to know ...
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1answer
1k views

Using Dalton's law of partial pressures

A container of volume $\pu{4.0 L}$ contains nitrogen at $\pu{25 °C}$ and $\pu{803 kPa}.$ This container is connected by a valve to another container of volume $\pu{10.0 L}$ that contains argon at $\pu{...
8
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3answers
9k 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 ...
4
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1answer
273 views

Is ash fireproof?

At high temperatures (almost) everything burns to ash. Is ash 'fireproof'? Is further combustion of ash possible for example by combining with hydrogen, oxygen, etc?
5
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1answer
570 views

Understanding dissolution of CO₂ in Selexol and Rectisol

I'm trying to understand pre-combusiton carbon capture processes as described in this presentation. I'm told that solvents such as chilled methanol ($\ce{CH3OH}$) and dimethyl ethers of ...
5
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1answer
1k views

Is there a similar characteristic of the lanthanide contraction in the other transition metal groups?

Basically, does the lanthanide contraction also occur with the 4d, 6d groups as well? I am at a lack of understanding in this topic, I am just wondering what specific elements does this jump in a ...
8
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1answer
51k views

Calculating the heat capacity of a calorimeter

I've been struggling with this problem that I can't seem to figure out. I think I know how to solve it but I think there's missing information. The combustion of 1 mole of glucose $\ce{C6H12O6}$ ...
7
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1answer
226 views

What is the 'ancestral term' in the LS coupling scheme?

On the physics.nist.gov site: http://physics.nist.gov/Pubs/AtSpec/node06.html The table titled "Atomic structural hierarchy in LS coupling and names for the groups of all transitions between ...
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441 views

multielectron spin-orbit coupling and energy level

For multi-electron atoms for which the Hamiltonian (including the spin-orbit coupling) reads $$H=\sum_i T_i-Z\sum_i V_i+\sum_i V_i^{\text{s.o.}}+\sum_{i>j}V_{ij}$$ The $T_i$ are the kinetic ...
19
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2answers
476 views

Can molecules diffuse upstream when emptying a cup of tea?

I was drinking some tea, and I randomly decided to pour some into the toilet in an unbroken stream; can particles travel "upstream" quickly enough to reach the mug of tea? How fast can diffusion occur ...
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2answers
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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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2answers
2k views

deduce chemical properties of a compound from elements

If we know the properties of two elements e.g Oxygen and Hydrogen. We know the following properties sound speed boiling point melting point refractive index etc. given that information, is it ...
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1answer
3k views

Moment of inertia for a triatomic molecule

What does the moment of inertia for a molecule mean? How is it useful? Most importantly, how would I go about solving it for a triatomic molecule?
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1answer
8k views

What is 'autogenous pressure'?

Compound 1 was hydrothermally synthesized under autogenous pressure[1] I've seen this term used a few times, but with no real explanation of what it means forthcoming. I suspect it refers to the ...
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2answers
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Is there a simple way to get the circular dichroism of a molecule from its structure?

Are there any heuristics to get the relative absorbtion of left and right circularly polarized light by a molecule from its molecular structure? Is it even possible to predict which polarization is ...
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4answers
379 views

Hierarchy of electronic wavefunctions

The previous question contained too much unnecessary information and was edited. I am wondering about the "hierarchy" of wavefunctions. If one can combine atomic orbitals (AO) into molecular orbitals ...
28
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1answer
15k views

Electrical conductivity of graphite

On this Wikipedia page, the electrical conductivity of various materials are given in the third column ($\sigma \text{ (S/m) at 20}^\circ \text{C}$). I am interested in the entry for Carbon (graphite)...
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3answers
10k views

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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1answer
838 views

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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5answers
7k views

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 ...
7
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1answer
933 views

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 ...
21
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3answers
454 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 ...
7
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1answer
287 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 ...
27
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2answers
1k views

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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1answer
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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2answers
4k views

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 ...
7
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1answer
4k 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 ...
20
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3answers
3k views

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. ...
10
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2answers
16k views

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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8answers
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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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1answer
648 views

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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4answers
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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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1answer
3k 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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6answers
1k views

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 ...
26
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3answers
22k views

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 ...
18
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1answer
724 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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1answer
6k 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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2answers
8k views

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. ...