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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21 views

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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15 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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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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1answer
37 views

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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24 views

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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12 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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4answers
76 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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31 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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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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17 views

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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1answer
30 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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12 views

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
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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24 views

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
79 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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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
8 views

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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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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1answer
51 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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25 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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22 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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1answer
431 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
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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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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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3answers
86 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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0answers
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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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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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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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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20 views

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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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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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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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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0answers
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
51 views

How much oxygen is formed in this first order reaction? [closed]

We have a reaction $$\ce{2N2O5 -> 4NO2 + O2},$$ which has a rate constant $k=6,2\cdot10^{-4}/\mathrm{min}$ at temperature $T=318.15\ \mathrm{K}$. How much oxygen is formed in litres when $1.00\ \...
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1answer
30 views

Calculating ΔH with non-integer coefficients in the balanced equation

I am working a practice problem out Ebbing's General Chemistry and for part of the problem I needed to calculate $ΔH.$ The problem considers the burning of ethane in oxygen to yield carbon dioxide and ...
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1answer
81 views

How would one determine an element simply by looking at its binding energy?

I am self studying MIT OCW chemistry 5.111 2014, one of the lecture questions states the following: Consider a neutral atom with 8 distinct electron binding energies: −14 eV, −28 eV, −94 eV, −218 ...
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22 views

Interface level between 2 components in Liquid-Liquid Extraction, What does it mean?

In LLE physical processes, there is this level (interface) between the 2 components (for example) that is being separated as shown in the picture. I know that the height of this level from the ...
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1answer
47 views

Why does snow sublime even when the surrounding temperature is below 0 °C? [closed]

Snow in winter below 0 °C, still sublimed very slowly over time. If I’m not mistaken, sublimation is an endothermic process. Where is this absorbed energy coming from when the surrounding temperature ...
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2answers
44 views

If water freezes at 32 °F (0 °C) at sea level, then what temperature does ice melt? [closed]

If water freezes at 32 °F, what happens to that newly formed ice at that temperature? Does it start melting as soon as it’s frozen, or does it require more heat to melt again? If it does require more ...
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1answer
24 views

Problem from Ionic Equilibrium [duplicate]

This seems to be a pretty easy problem but I cannot understand why we do not consider the contribution of $\ce{H+}$ ions by water (water dissociates into $\ce{H+}$ and $\ce{OH-}$) and only that of $\...
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2answers
861 views

What is the difference between chemical equilibrium and dynamic equilibrium?

Is chemical equilibrium and dynamic equilibrium the same thing? Both point to the reversible reactions and no net changes in the concentrations of product and reactant. Dynamic equilibrium from ...
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1answer
29 views

Why does eutectic point has three phases, but consolute point has two phases?

At eutectic point, there are three phases: solid A, solid B and homogenous liquid phase containing both A and B. But at consolute point, we are told it has 2 phases: liquid A and liquid B. Why isn'...
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1answer
101 views

Are these numbers Madelung constants?

I have no idea of chemistry, just a little bit what I know from school, but I found through some search some connection between entropy (Shannon entropy) of the divisors of some natural numbers and ...
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2answers
60 views

Hess's Law and ΔH

Target equation: $\ce{Mg(s) + 1/2 O2 -> MgO(s)}$ $$ \begin{align} \ce{MgO(s) + 2 HCl(aq) &-> MgCl2(aq) + H2O(l)} &\quad ΔH &= \pu{-1300 kJ} \tag{1}\\ \ce{Mg(s) + 2 HCl(aq) &-&...
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1answer
27 views

Is it possible to calculate the 'overall' redox potential of a system?

For a solution where many redox reactions occur (e.g. cytosol, soil solution), can we consider anything as 'overall' redox potential of a system? Is there a formula to quantify it in relation to the ...
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1answer
79 views

Why could it be assumed that the standard enthalpy change is independent of temperature down to 25 °C?

For the reversible reaction of pyruvic acid to 2,2-dihydroxypropanoic acid, we calculated enthalpy using NMR and extrapolated from area (integration) and peaks etc. We then plotted $\ln K$ vs $1/T.$ ...