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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questions
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Kinetic energy of electrons emitted in Photoelectron Spectroscopy
In multiple sources (example), I found the information that the kinetic energy $E_k$ measured using (Ultraviolet / X-ray) Photoelectron Spectroscopy is given by:
$E_k = h\nu - B.E._F - \phi_{spec}$
...
24
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5answers
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Why does radium have a higher first ionisation energy than barium?
I'm wondering why radium appears to buck the general trend that first ionisation energies decrease as you move down a group in the periodic table: barium (the group 2 element preceding it) has a first ...
9
votes
1answer
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Why is the relative atomic mass of carbon not exactly 12?
Relative atomic masses of atoms of all chemical elements are numbers without units, being the value of proportion compared to $\frac{1}{12}^\text{th}$ the mass of the carbon atom.
But the relative ...
4
votes
2answers
861 views
How to derive partial gas equation?
If the following gasses are to mix, what is the partial pressure of neon?
The correct answer is 0.1. I cannot figure out how my professor derived this equation. From the ideal gas law, all I ...
6
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2answers
344 views
Classical reason for good heat conductance in diamond?
My teacher in my physics course attributed this effect to phonons, more here, but I am skeptical about this argument, it feels like he is overlooking the whole question -- what about with Silica that ...
7
votes
1answer
890 views
Does sublimation happen only on the surface or throughout the body?
Like evaporation happens only on the surface of a liquid, and boiling/vapourisation takes place throughout the body, how does sublimation occur? Why?
8
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1answer
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Simultaneous equilibria
Rephrasing:
The following reactions are a small example of my big system
$$(1)\ \ce{A + B <=> AB}$$
$$(2)\ \ce{AB -> CB}$$
$$(3)\ \ce{A -> C}$$
$$(4)\ \ce{C + B <=> CB}$$
with
$...
-3
votes
1answer
449 views
Can we create a galvanic cell with only half a cell connected to the ground? [closed]
I have a question about electrical potential in galvanic cells ,suppose that we have only half a cell wich means that we have only one Ox/Red couple (one metal and the other as ionic solution ...)...
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5answers
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Why don't the electrons move through the electrolyte (instead of the circuit) in a galvanic cell?
I was learning about galvanic cells and I had a problem understanding why electrons do not travel through the electrolyte solutions themselves, instead preferring to travel through metals. Can ...
2
votes
1answer
2k views
How do I calculate partial pressure here?
I need some help with partial pressures of reactions for a fuel cell project. The overall reaction for a fuel cell is
$$\ce{H_{2} +\frac{1}{2}O_{2}->H_{2}O}$$
Which means that the mole fraction ...
33
votes
4answers
8k views
What exactly is happening when sodium, potassium, or other alkali metal explodes in water?
There are lots of videos on YouTube showing sodium, potassium, etc. exploding when dropped into water (this, for example).
I understand that when an alkali metal is exposed to water, a violent ...
6
votes
1answer
242 views
Reduction and re-oxidation of TiO₂
I'm having a hard time finding data about an experiment that I know has been done a bunch of times:
I have a sheet of single crystal rutile $\ce{TiO_{2}}$ (110) that I want to reduce to various $\ce{...
6
votes
3answers
20k views
Electronegativity of zinc vs copper in galvanic cell
I am reading up on how galvanic cell works and I realised that the flow of electrons is from Zn to Cu. But Zn is more electronegative compared to Cu according to periodic table trends
I read it ...
9
votes
2answers
1k views
Why does gas particle velocity affect rate of effusion?
I understand why smaller particles have more velocity, but I don't understand what velocity has to do with rate of effusion:
My reasoning is thus:
Pressure is the number of impacts of particles in a ...
8
votes
1answer
155 views
Why does hydrogen form on such a long time scale?
If we were trying to figure out the time scale for a gas-phase reaction between two hydrogen atoms in a molecular cloud (which has density $~\pu{10^4cm^-3}$), apparently the reaction would happen on a ...
11
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3answers
3k 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 ...
6
votes
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
450 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
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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?
0
votes
1answer
544 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}...
8
votes
3answers
11k views
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 & ...
1
vote
1answer
285 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
14k 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{...
12
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2answers
3k views
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?
4
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0answers
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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
votes
1answer
540 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
2k 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 ...
2
votes
1answer
1k views
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 ...
3
votes
1answer
988 views
Dalton's Law Of Partial Pressures
I'm given a container of volume of 4.0 Litres that containes Nitrogen at $25 ^\circ C $ and 803 kPa.
This container is connected by a valve to another container of 10.0 litres volume that containes ...
8
votes
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
votes
1answer
253 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
votes
1answer
558 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
votes
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
votes
1answer
46k 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
votes
1answer
219 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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0answers
428 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 ...
18
votes
2answers
446 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
2k views
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
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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 ...
4
votes
1answer
2k 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?
10
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1answer
7k 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 ...
20
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2answers
2k views
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 ...
16
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4answers
359 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 ...
27
votes
1answer
14k 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
9k 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
808 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
votes
1answer
922 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 ...
20
votes
3answers
439 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
votes
1answer
275 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 ...
