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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86 views

In an isothermal process, how can the change in internal energy be 0?

It was written in my textbook, $$ \mathrm{d}U = \left(\frac{\partial U}{\partial T}\right)_V \mathrm{d}T +\left(\frac{\partial U}{\partial V}\right)_T \mathrm{d}V $$ If the process is isothermal,...
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Greater ligand stabilization of the lower oxidation state increasing redox potential

According to Atkins, P.W., De Paula, J. and Keeler, J., 2006, Atkins' Physical Chemistry, $$\ce{[Fe(CN)6]^3- + e- <=> [Fe(CN)6]^4-}\tag{R1}$$ has Eo = + 0.36 V, whereas $$\ce{Fe^3+ + e- <=&...
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2answers
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Clarification required on whether to use $C_v$ or $C_p$ in this question on finding entropy change

$1 \text{ mol}$ of an ideal monoatomic gas at $300 \text{ K}$ is subjected to a reversible isentropic compression process until final temperature reaches $600 \text{ K}$. If initial pressure is $1 \...
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Basic thermodynamics question about work

I am getting into thermodynamics, and I have a basic fundamental question about the definition of the change in internal energy $\mathrm{d}U$: $\mathrm{d}U = T\,\mathrm{d}S - P\,\mathrm{d}V + \sum\...
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28 views

Hartree-Fock vs. DFT vs. Hohenberg-Kohn vs. Kohn-Sham

What is the difference between these four approaches? My current understanding is that Hartree-Fock uses only 1 slater-determine (accounting for antisymmetry) but neglects correlation between ...
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1answer
79 views

Which solvent is good for using SU-8 particle in Optical tweezers?

I'm studying Optical tweezers. I've used Polystyrene for samples. Nowadays, I've got SU-8 pillar. I wanna use that for sample, but its density is heavier than water. I can't use that. So I wanna know ...
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1answer
94 views

What are the disadvantages of using the InChI format?

What are the disadvantages (if any) in producing and using the InChI format of chemical compound representation in chemoinformatics? Are there any particular problem one can face when using InChI?
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1answer
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Difference between equations for spectroscopy wavenumbers

What is the difference between these two equations and when is appropriate to use which one? We were told that $F(J)$ in this case is $F(J)= E/h$ for units in frequency And $F(J) = BJ(J+1)$ $\...
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Rotational spectroscopy application of different equations [duplicate]

So we were given two problems and I don't understand why one was solved one way, and another was solved another way Estimate the bond length of 12C16O (pure rotational spectrum) given J''=3 (15.356 ...
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Tight binding model with Extended Huckel Approximation

I've been reading Albright's Orbital Interactions in Chemistry. In the chapter on solids, he provided a general approach to find the band structure of a solid state system Now if we are to model a ...
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2answers
6k views

Why does a hard-boiled egg have more entropy than a normal egg?

The question "Why does a hard-boiled egg have more entropy than a normal egg?" was recently asked on one of my tests. I said that entropy will decrease as a hard boiled egg has molecules in a more ...
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5answers
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What roles do neutrons play in an atom?

An atom typically consists of electrons, protons, and neutrons. Electrons are negatively charged and participate in bonding to stabilize the atom. Conversely, protons are positively charged and ...
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1answer
31 views

Electrochemistry conditions for voltage to increase in a galvanic cell

I understand that increasing the concentration of reactants in a galvanic cell generally causes the voltage of the cell to increase. But is that really the case always? Consider a standard cell of ...
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0answers
33 views

Tight binding model for nanoparticles as finite systems

I'm still trying to calculate the band structure ab initio for some hypothetical nanoparticles. It seems that I can directly build a tight-binding model by forming Bloch functions, numerically ...
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14 views

Magnitude of Coulombic integral of atomic orbitals

I'm wondering anyone knows what's the typical magnitude for Coulombic integral of atomic orbitals in large molecules (not simple diatomics). Also, is it right to say that the integral has a greater ...
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0answers
28 views

Methylhydrazine Calorimetry

Below is a chemistry practice problem. I am curious why the change in heat of the oxygen molecules doesn't affect the calculations. Methylhydrazine ($\ce{CH6N2}$) is commonly used as a liquid ...
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1answer
52 views

Rotational Energy Levels

Why does the rotational constant B decrease and transition spacings decrease as the mass of a particle increase? I understand from a purely equation perspective that since $$B = \frac{h} {8\pi ^2 ...
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0answers
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Outline the steps involved in the Hartree–Fock method for the calculation of molecular electronic structure [duplicate]

I understand that the steps of the self-consistent method are as follows: guess the form of Psi(r) use psi(r) to evaluate for V1eff(r1) then solve for a new psi(r) the two wavefunctions tend to ...
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3answers
872 views

Ellingham Diagram

My textbook says the following about the Ellingham diagram: Each plot is a straight line except when some change in phase ($\ce{s -> liq}$ or $\ce{liq -> g}$) takes place. The temperature at ...
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0answers
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Inductively Coupled Plasma and Mass Spectrometry

I was doing some homework and I was reading about how ICP is suitable for mass spectrometry and it said how its high temperature favours ionization which is good in MS. But also, because the ...
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1answer
80 views

Difference between Particle in a Box and Harmonic Oscillator approximations

Why in the particle in a box model do the values of n begin at 1 but in the harmonic oscillator they begin at 0? I understand what the wave-functions and their corresponding probabilities look like ...
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2answers
90 views

Why when deriving the Clapeyron equation can you assume that dH = dq, as surely the pressure is not constant?

Part of the Clapeyron equation involves replacing $\Delta S$ with $\Delta H/T$. I can see the step from $\Delta S$ to $\Delta q/T$ but I'm not sure why you can replace $\Delta q$ with $\Delta H$. From ...
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Does H2C=C=C=CH2 lie in the same plane? [closed]

explain in terms of bonding theory why all atoms H2C=C=C=CH2 must lie in the same plane
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1answer
22 views

Calculating partial pressure with 3 equilibrium equations [closed]

So my friend had sent this question to me some days ago and it seems I still am not able to solve it. I am confused whether the amount of A that dissociates in the first equation would account for the ...
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0answers
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Atomic structure what is binding and ionisation energy [closed]

What is the difference between ionisation energy and binding energy if not then what is similarity between them
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0answers
15 views

Can Electronegativity be explained through QM? [closed]

Even as senior in high school, I still find chemistry quite intimidating, partly due to how vast it is and partly because I don't understand when something stated in Chemistry is experimentally ...
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1answer
32 views

Determine bond length via rotational spectroscopy

Estimate the bond length of 12C16O (pure rotational spectrum) given J''=3 (15.356 cm-1) and J'=9 (38.356) I understand that the first step is the calculate the rotational constant. So to do this I ...
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2answers
313 views

Is the equation dG = Vdp − SdT valid only for a reversible process? Can it be applied for an irreversible one too?

In the derivation, we write: $$ \begin{align} G &= H - TS &\quad&\to&\quad \mathrm dG &= \mathrm dH - T\,\mathrm dS - S\,\mathrm dT \\ H &= U + pV &\quad&\to&\quad ...
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1answer
1k views

How can I calculate the percentage of dissociated dinitrogen tetroxide?

When $\pu{36.8 g}$ $\ce{N2O4(g)}$ is introduced into a 1.0-litre flask at $\pu{27 °C}$ the following equilibrium reaction occurs: $\ce{N2O4(g) <=> 2NO2(g)}$; $K_p = 0.1642~\mathrm{atm}$. ...
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2answers
558 views

Effects of pressure on equilibrium [closed]

Which system at equilibrium will not be influenced by a change in pressure? $$ \begin{align} \ce{3 O2(g) &<=> 2 O3(g)}\tag{A}\\ \ce{N2(g) + 3 H2(g) &<=> 2 NH3(g)}\tag{B}\\ \ce{...
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88 views

Order of reaction in adsorption process

(1) $\ce{PH3(g) <=>[W]PH3(adsorption)->[W]P(s) + 3/2 H2(g)}$ The decomposition of phosphine on tungsten surface at low pressure is a pseudo first order reaction. This is because the rate of ...
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1answer
52 views

The reaction rate when the rate-determining step has a back reaction

For some reason, I am reviewing general chemistry and I find that the elementary reaction for the rate-determining step (RDS) is assumed to be irreversible, that is, single arrow, in all questions ...
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3answers
91 views

Degree of dissociation of weak electrolyte at infinite dilution

Why the degree of dissociation of weak electrolyte is 1 at infinite dilution and how do we get the result? Like I know that at infinite dilution the concentration of solution is 0 but what does that ...
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1answer
443 views

What is J in the rigid rotor model?

In my class notes regarding the rigid rotor model, J is described as simply the angular momentum (replacing roe or p) and is also referred to as the angular momentum quantum number. Are these two ...
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0answers
26 views

What is the difference between dynamical and non-dynamical correlation and which one is accounted for in Hartree-Fock theory? [duplicate]

It is my understanding that dynamical is related to the movement of individual electrons. I don't fully understand what this means though. Non-dynamical correlation is still very unclear from my ...
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1answer
36 views

Why can a wave-function be written as a product of 1-electron wave-functions?

Why can a wavefunction be written as a product of 1-electron wave-functions when making approximations to solve atoms other than hydrogen? (ie. helium) We used this when solving multielectron systems ...
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0answers
23 views

Finding the wavelength of maximum absorption and Crystal Field Splitting of [Ni(H2O)6]2+

(I haven't been here for a long time, so tell me if my formatting is fine) Given The $\ce{[Ni(H2O)6]^2+}$ complex appears green in solution from the transmitted light. Estimate the wavelength of ...
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0answers
32 views

Can we break double bonds by using laser and heat?

If it is possible then give an example for it. That chemical reaction is in this process. step 1: {Reactant + heat(sunlight)} gives weakened bonded product1 step 2: {product1 + laser} gives {one solid ...
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0answers
15 views

Is dz2 orbital having lobe in z axis direction is larger than other d orbitals? [closed]

I have seen in one video that dz^2 orbital is formed with d(x2-z2) and d(y2-z2) and hence its lobe in z axis become large due to overlap so is it mean that dz2 lobe in direction of z axis is larger ...
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0answers
17 views

Neither Raman nor IR Active vibrational modes of water [closed]

How can we find vibration modes of water that are not in IR and Raman spectroscopy? I thought these modes creat when a transition happens between 2 modes i.e from mode to another mode.
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24 views

Higher Experimental Optical activity compared to literature values [closed]

If you have a sample of an optically active substance it has a specific angle of rotation. Lets say the substance I produced had a value of 56 degrees but the literature value for my substance should ...
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2answers
61 views

Relation of temperature and intensive property [closed]

I came across a question that inquired about whether there exists any intensive property of a system, that is independent of temperature and then seeks proof for the presence/absence of such ...
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0answers
72 views

Anomaly in van der Waals constants of noble gases

In van der Waals equation for a real gas, the equation is $$\left(P + a\frac{n^2}{V^2}\right)(V - nb) = nRT$$ where $P$ is the pressure of the real gas, $n$ is the number of moles of the gas, $R$ is ...
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1answer
51 views

What all information can be gathered qualitatively from the radial distribution functions of a molecule?

Apart from knowing the radius of coordination shells and the probability of finding, is there any other thermodynamic information we can gather by looking at radial distribution functions of a ...
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2answers
37 views

What does it mean to balance a redox reaction in acidic or basic mediums? [closed]

Until now it was clear to me what balancing a reaction was. Balancing redox reaction also make sense to me. What does it mean to balance a redox reaction in acidic or basic medium?
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Clarification on temperature-composition phase diagrams of a Binary Mixture

After watching this video: https://www.youtube.com/watch?v=SPrybbPdVDQ, I have come to the conclusion that on a temperature-composition curve(for two components, $\mathrm{A}$ and $\mathrm{B}$), there ...
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43 views

How much CO2 can I fit in a 0.5 L plastic bottle?

Let's say I have a 50 lb CO2 tank which can probably contain about 1000 L of the gas at 122 atm. Suppose I want to use the tank to fill a 0.5 L plastic bottle which only has air in it. We know that ...
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0answers
28 views

What is the product of the reaction between hydrogen peroxide and ammonium thiocyanate?

Title. I saw a video showing 30% hydrogen peroxide being dripped onto ammonium thiocyanate. https://www.youtube.com/watch?v=fQju2e8CMPY I am wondering what the product of that reaction is. The people ...
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48 views

Why isn't the total energy of an atom the sum of the orbital energies - what is I1 and I2?

We were told that the total energy of a helium atom is not the sum of its orbital energies and that this is Koopman's theorem. This sortof makes sense but I am struggling with contextualizing it. i....
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1answer
3k views

Number of octahedral and tetrahedral voids present in a HCP structure

The given image depicts the tetrahedral and octahedral voids in HCP structure. For the tetrahedral part I figured out that there would be 6 tetrahedral voids in total. My visualisation: In the ...