Questions tagged [physical-chemistry]
Study of macroscopic and microscopic phenomena in chemical systems in terms of physical laws and concepts [thermodynamics, statistical mechanics, kinetic theory, quantum mechanics...].
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How many degrees of freedom does the water molecule have? [duplicate]
This is mainly a question about molar heat capacity. I've read many different values for the degrees of freedom of water, for example f = 12 on (https://en.wikipedia.org/wiki/Molar_heat_capacity).
But ...
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Patterns on melted, then solidified chocolate
Observation
I have melted some chocolate (in a bain-marie, or water-bath) in a bowl, and then turned off the stove. I let the hot and liquid chocolate stand there, letting it cool for a few hours at ...
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Can ions dissolved in a solution be separated by a magnetic field?
When an ionic compound is dissolved in a polar solvent (eg. salt dissolving in water), the ions disassociate and float freely in the liquid. An electric current flowing through the solution can then &...
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Thermodynamics and Gibbs energy
The equation for the Gibbs free energy is: $\Delta G = \Delta H - T\Delta S.$
$\Delta H$ is the amount of energy difference between the initial state (characterized by $U_{i}$, $S_{i}$, and $V_{i}$) ...
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Thermodynamics and entropy
In a thermodynamics process, when heat is exchanged ($\Delta H$), it causes a change of system from state 1 to state 2. As a result, the entropy of a system is changed irreversibly.
Can the change in ...
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Interpretation of non-spontaneous Gibbs free energy
Good day guys,
I was reading some books on physical thermodynamics, they explain that for system undergoing a chemical reaction whose $\Delta G < 0$ indicating that the reaction can then provide us ...
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Total energy of a rocket launch
I'm wondering how the total energy of a combined Earth-rocket system is conserved in a rocket launch?
Before launch, kinetic and gravitational potential energy of the rocket are 0. It then launches, ...
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How is energy conserved in formation of chemical bonds?
I understand that when an H$_2$O molecule is formed, it has lesser total energy than the constituent (2H and O) atoms. I also understand that the potential energy (PE) will be reduced when the atoms ...
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Can I taste electrolysis?
This is a silly question, but can it be done safely? My friend wanted to have a soup with electrolysis causing it to taste differently on each side of the bowl. I think this is dangerous, because ...
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The equipartion theorem and degree of freedom in case of vibration
I have been taught in chemistry that,
the energy of a vibrational freedom is $RT$ (ie, twice that of rotational/translational)
The degree of freedom which I found in chemistry, for the vibrational ...
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Is it possible to use a water molecule's expansion/contraction effect with heat as a motor?
When water molecule is cooled, it is well known that it expands:
That's the reason the rocks in the desert explode in the cold of the night: the rocks have water inside that expands with cold and ...
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How do relativistic effects lead to gold not usually occuring in a 2+ oxidation state?
In the literature I found compounds where gold occurs in a 1+ and 3+ oxidation state, like the perovskite CsAuCl_3, and also came across the fact that gold usually doesn't occur in a Au2+ state. ...
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An egg gets soft before it gets hard [closed]
I found in a book from 1500's that says that when you cook an egg (I assume a raw egg), it will get softer before it gets harder. Is that accepted by the science community today? Can someone explain ...
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What melts faster at room temperature, frozen salt water or frozen fresh water? [duplicate]
Suppose you freeze 2 ice cubes in the same freezer at -6F. One cube is pure water, the other is a saltwater cube. Take both cubes out of the freezer at the same time and put them into a room at say ...
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Convolution or addition? Proper way to model overlapping absorption line profiles
Suppose you obtain a measured spectral line shape (let's call it 'envelope') which appears as a skewed/asymmetric voigt profile. You know physically that the envelope line profile has this skew ...
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Does fire cause friction in the fuel?
It is possible to create fire by friction. For example - by striking a stone with another stone or by striking a matchstick on a rough surface.
My question is: Can we say that, where there is fire ...
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Measurement of dipole electric field generated by a polar molecule
I'm trying to understand the nature of polar molecules. Have there been experiments where we can say to have actually measured the dipole electric field generated by a polar molecule such as hydrogen ...
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Enthalpy but why "add work back in"? Why internal energy $U$ was not enough? [closed]
The concept of Enthalpy has bugged me for quite some time. I just can't understand its meaning or reason for being.
Open|flow system enthalpy:
I think I fully understand why H is used in flow ...
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What is the interpretation of the matrix elements of a second order perturbation capturing dipole-dipole interactions between two molecules?
The system I am studying is one molecule comes in close proximity with another molecule, and we are interested in calculating the energy of the resulting induced dipole-dipole interactions. I want to ...
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Are there any indications that the hat polykite or spectre appear as aperiodic structures in materials?
It is known that certain aperiodic structures appear in quasichrystals. For instance, Daniel Schechtman and Ilan Blech discovered that the aluminium-manganese alloy Al$_{6}$Mn has no translational ...
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Can a matter enter do work without being consumed up? [closed]
I had a tricky question in mind. So, I wanted to use the example of Catalysts (In chemical reactions) as an example. It's said that when catalysts enter a chemical reaction, they're Never consumed up. ...
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What makes a book (or a stack of paper) so sturdy under pressure?
I've watched an experiment where they compress a book with a hydraulic press, and the book appears to stay relatively intact under that pressure. It is mentioned that the hydraulic press has a 100-ton ...
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How much salinity is needed for everyone to float?
Everyone floats in Dead Sea because it is so salty. Is it true in Great Salt Lake? How about Red Sea and Mediterranean Sea? Is it impossible for anyone to sink in these seas without added weight?
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What are some liquids with high ranges of refractive index with change in temperature?
I need to run an experiment on the effect of temperature on refractive index of a liquid, and in order to make the change most visible and have the lowest percent uncertainty I need the change in ...
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How to think about thermodynamic equilibrium in terms of virtual displacements?
I am currently taking thermodynamics and am finding the concept of thermodynamic equilibrium rather difficult to grasp. My textbook gives a definition in terms of the virtual displacement of with ...
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What effect does salt have on the boiling speed of water?
My question is the following:
I have two pots. Pot A and pot B. I fill both of them with 1l (litre) of water. Now I add a table spoon of salt into pot A. Which water is going to start boiling first?
I ...
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Inverse relationship between salinity and conductivity?
I have a salt solution that is saturated at 40C, I measured conductivity and got 440 ms/cm.
I then increased the temp to 50C, add more salt until the solution is saturated again, and measure ...
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What is $Z$ in collision theory of chemical reactions?
According to collision theory given by Max Trautz and William Lewis the rate of chemical reaction is proportional to $Z$ (number of collision per second per unit volume of reaction mixture)
Suppose a,...
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The action of anti-bumping granules
Anti-bumping granules are usually small stones. I presume that the principle of these granules ensuring smooth boiling, is that it blocks the upward motion of solution molecules.
Usually the stones ...
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Relation between Sherwood and Peclet numbers
What's the relation between Sherwood number and Peclet number for mass transfer in a rectangular channel with fully developed laminar flow?
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Isenthalpic process and heat involved [closed]
In the given question as in photo we are asked to calculate heat involved in isenthalpic process. Since isenthalpic means ΔH = 0 and we know enthalpy is the heat content at constant pressure.As in ...
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Why can't there be an "outside loop" in a perfectly insulated container with infinite time?
So I am having this arguement with my brother and wanted to ask other people.
It might be more of a chemistry question but Why can't there be an "outside loop" in a perfectly insulated ...
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Electric dipole vs density gradient
Chemist here, so please excuse me for asking trivial stuff.
I am trying to represent the electron density of a molecule as a bunch of point charges.
One program that I use can calculate electron ...
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Term symbols and the role of antisymmetrization
In the Hartree-Fock method for many-electron atoms, for a given eigenspace $\mathscr{E}$ of the unperturbed Hamiltonian (in a.u.)
$$\hat{H}=\sum_{i=1}^Z \Big(-\frac{1}{2}\nabla^2_i-\frac{Z}{|\vec{r}_i|...
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How do you know mercury changes monotonically with temperature if mercury itself is used to make the thermometer?
In the book I am reading recently "Concept of physics" volume 2 by professor H.C. Verma it says that (I am just summarizing the main points chronologically)
Energy is transferred from hot ...
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Understanding enthalpy and gibbs energy changes in a reaction
I was looking at the enthalpy change for water-splitting reaction:
$$ \Delta H^o_R = [\Delta H^0_{H_2(g)} +\frac{1}{2}\Delta H^0_{O_2(g)}]-\Delta H^0_{H_2O(l)} = 285.83 kJ/mol$$
According to the ...
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What is the diffusivity of colloidal Formazine in water?
I have synthesized Foramzine in an aqueous solution (turbidity = 4000 NTU), and will be further diluting it. I would like to know the diffusion coefficient (diffusivity/mass diffusivity) of colloidal ...
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How small can velcro be?
Note: "fiber" refers to individual hooks and/or loops.
Imagine two flawless graphene sheets, one with atomic diameter hydrocarbon loops attached to one face, one with atomic diameter ...
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Which law applies to the whole concentration range?
If we are talking about two-component solutions can Henry's law be applied to the whole concentration range?
From what I understand Raoults and Daltons are used for smaller concentrations.
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How is the energy content in 1 kg of water and petrol the same?
We know petrol is a fuel and water is not. But how come 1 kg of water and 1 kg of petrol have the same energy content? The total energy is given by $E=mc^2$, it says nothing about the chemical ...
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Why do dry lentils cluster around air bubbles?
When I pour dry lentils into a water bowl, I notice many of them form little clusters, with an air bubble in the center.
Why does this happen? I'm guessing something about static electricity. But not ...
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How much $\rm CO_2$ can you save by overfilling a SodaStream bottle? [closed]
For people who don't know what Sodastream is: SodaStream is a system where you can make your own soda at home using regular water and a CO2 cartridge. You put water in the special Sodastream bottle, ...
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Chemical Potential and Gibbs Energy
In my reading of thermodynamics, the chemical potential $\mu$ of a system is often defined as the Gibbs free energy per unit particle (or mole, for my chemist friends) of substance. Then, for a system ...
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When a shaken soft-drink botte is left to calm down, does it return to the same state as before being shaken?
We had a disagreement with a friend:
When a soft-drink (carbonated) bottle (e.g., 1.5l) is shaken or dropped on the floor, if opened immediately it will spill out. However, if it is left to "calm ...
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How fast do $\rm CO_2$ molecules transfer between air and water at equilibrium?
Suppose a bath of water is in equilibrium with the air above it at temperature T and pressure P. The concentration of $\rm CO_2$ in the air is, say, 400ppm, and the concentration of $\rm CO_2$ in the ...
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Do particles (e.g. atoms/electrons) in large molecules that rotate experience pseudoforces?
Imagine if you have a molecule with a large size, e.g. proteins.
Anything that rotates experiences pseudoforces if my understanding is correct (e.g. coriolis, centrifugal etc).
Since every molecule ...
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How does non-polar solutes dissolve in non-polar solvents?
My actual question is that i want to know the molecular interaction can all takes place between non polar solvents and non polar solutes and also i want to know that why does some non polar substance ...
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How does some non-polar molecules dissolve in water?
My textbook says:
Similarly, non-polar (i.e., covalent or organic) compounds like naphthalene, anthracene etc. are soluble in non-polar (i.e., covalent or organic) solvents like benzene, ether, ...
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Why $\rm ZnO$ looks transparent?
I'm looking for the reason transparent of $\rm ZnO$ and found out nanoparticles of $\rm ZnO$ do not scatter reflected light
can I conclude like this: material can be transparent if pass light or ...
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Can a broken chemical bond be made again?
My question is that if we raise the temperature of a substance carrying chemical bond …….then will the bond be made again by itself by cooling down the temperature?
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