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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How can a volatile solvent make an ideal solution with a non-volatile solid solute?
I ask because to make an ideal solution the intermolecular forces between the molecules of solvent and solute respectively should be similar and after mixing they should also be similar to what they ...
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Heat capacity of (ideal) gases at constant pressure
I've come across this article which says that the constant pressure heat capacity is independent of pressure.
It also gives a mathematical explanation which says that any work of an ideal gas at ...
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Why do we consider one elementary reaction to be in equilibrium while calculating rate law for complex reactions?
When we calculate rate of reaction pfor a complex reaction, if the rate determining step have intermediates, we calculate the rate of reaction using the step which is at equilibrium (and doesn't have ...
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Fluorescence and resulting vibrational state
I was taking a look at Jablonski schemes and had some doubts regarding it. Now assume a regular molecule which follows this Jablonski scheme:
We can see that when molecules absorb certain quantized ...
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What the book means for "percentage difference"?
From Atkins-De Paula, Physical Chemistry, Ninth Edition, page 485
Not sure what the books means as "percentage difference".
Btw, this is my attempt
Fundamental vibration, in wavenumber, ...
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Is fugacity the corrected pressure that should be used in thermodynamical models?
I am a little confused about fugacity and pressure of a gas. In ideal gases, pressure is same as fugacity. But for real gases this is not the case. Here is the link of the question that is the source ...
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Ionization and exchange energy [closed]
As we all know that 'Nitrogen' has higher 'Ionization Energy' than its neighboring elements both carbon and oxygen, opposite to the trend of increasing ionization energy across a period. The reason ...
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Is it a convention to divide rate of reaction by stoichiometric coefficient?
If we consider a reaction
$$ \ce{A + B -> 3 C} $$
The rate of reaction is given by
$$ R= -\dfrac{\Delta[A]}{\Delta t} = -\dfrac{\Delta[B]}{\Delta t} = \frac13\dfrac{\Delta[C]}{\Delta t} $$
I know ...
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Are there materials or molecules where fast internal conversion is desirable?
For light-emitting devices fast internal conversion is typically considered as a downside as it competes with fluorescence and phosphorescence. A low internal conversion rate is thus typically desired ...
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Biocompatible, high refractive index medium for 780 nm?
I am trying to find a medium for optics experiments on living cells. I have been using yeast cells, saccharomyces cerevisiae and saccharomyces boulardii, and need a medium with refractive index (RI) ...
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Why my mineral water from different sources do not mixed well? [closed]
Background:
In 8 hours range, I have bought cold mineral water (brand A), then refill the plastic bottle with cold mineral water (brand B) from my office. As far i know, brand B has high pH while ...
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Table of molecular orbital extents — what does it even mean? [closed]
In molecular orbital theory, the term molecular orbital extents was mentioned, although I can't really picture it. Does molecular orbital extent refer to the spatial distribution of electrons in a ...
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Qualitative explanation for equal heat capacities in ideal gases
Hello I was wondering the following thing. As you all know from statistical thermodynamics, if only translational states are available for a given ideal gas (such as He, Ne, Ar, Xe), the isochoric ...
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Calculating Rotational Temperature from an FTIR Spectrum
I am trying to calculate the rotational temperature of a sample of gas phase HCN from an FTIR spectrum. It's a 10 Torr sample in a 10 cm gas cell, held at room temperature. In theory, I should be able ...
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Why decomposition of gas on metal surface at high pressure considered 0 order
While reading my textbook it says that when ammonia decompose on a platinum surface at high pressure, the reaction is 0 order because at high pressure the metal surface get saturated with ammonia ...
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Ways and ideas to study ym rough surfaces with scanning tunneling microscopy
We want to study porous carbon (with nanoparticles, e.g., FeO, Ni, Au, La, Ir, Ag ...) via STM. But we run into the problem that the surface is very rough. As seen in Figure 1.
Thus there is an ...
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Is the line between physisorption and chemisorption species specific?
I was studying about heterogenous catalysis, and my Professor said something along the line, "When the adsorption energy is comparable to (or lower than) heat of evaporation, then it is ...
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How to find the ligand field splitting of d orbitals in a square planar complex?
I am working with a Iron square planar complex with $\ce{NH2-}$ and $\ce{OH-}$ ligands having cis and trans conformation. My question is how to theoretically/computationally calculate the ligand filed ...
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Why isn't residual standard deviation used in FQY analysis?
I've been measuring relative fluorescence quantum yield (hereafter FQY) for a photosensitive pigment. Most analytical articles and standard operating procedures (SOPs) I've read suggest taking the ...
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Why does oxidation of gold with oxygen work in cyanide leaching?
Normally gold can't be oxidizes by oxygen, but in the presence of $\ce{CN}^-$ it works.
In general, I have understood that this is due to the fact that complexation $\ce{[Au(CN)_2]^-}$ decreases the ...
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Non-Arrhenius temperature dependence of bimolecular reaction rates at very high temperatures
Once I have read that in some cases bimolecular reactions can exhibit a maximum as a function of temperature due to the short lifetime of the activated complex at very high temperatures.
At low ...
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Why heat capacity at constant volume relates to change in volume
I have been dealing with the establishment of a relationship between $w$, $q$, $\Delta U$ and $\Delta H$. I think the entire derivation is not necessary here so I will elaborate until the concerned ...
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Can excited electronic states also decay due to collisions?
I was wondering if electronic states could decay due to collisions and not by fluorescence?
Just like vibronic relaxations can happen, when vibrationally excited molecules can lose those extra modes ...
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Which of the given samples will have the largest number of atoms? [closed]
The samples that we have in question are as follows:
1g Au
1g Na
1g Li
1g Cl2
I know that the sample of element which has the largest number of moles of atoms of the element must have the largest ...
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RMS Speed of Gases as Standard Deviation
In kinetic molecular theory, the average velocity of gas particle is zero since the molecule move in different directions, and the overall effect is zero. Howeever, you can calculate different speeds.
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Help with exchange integral interactions!
A single determinant configuration constructed in a basis with 7 spatial orbitals has the following exchange integral interaction energy terms:
-2K12 -K13 -K23 -K14 -K24
(i) Draw a configuration that ...
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Why is prismane explosive but cubane is not?
So I was reading about polyhedral hydrocarbons, because I dig the topic, and I read (admittedly on wikipedia entries... But they cited papers, I swear!) that prismane is explosive due to the massive ...
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Why is silver(I) phosphate so unexpectedly thermally stable?
Silver(I) oxide is completely decomposed in air already at $\pu{300 °C}.$
Formulate the decomposition reaction and the corresponding mass action expression.
$\ce{Ag3PO4}$ can be melted at $\pu{800°C}$ ...
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Why is electrochemical potential defined as sum of electrical potential and apparent electrical potential energy?
Engel and Reid's Physical Chemistry [1, p. 308] defines the electrochemical potential in terms of the charge in units of the electron charge $(z),$ Faraday constant $(F),$ and electrical potential $(\...
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What is the physical significance of the frequency factor in the Arrhenius equation?
As the title says, I am wondering what the physical significance of the frequency/pre-exponential factor in the Arrhenius equation. My idea of it is that:
If the units of $E_a$ are energy per molecule,...
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Electrolysis of gasoline (or other uniform liquid hydrocarbon) [closed]
Electrolysis, when I usually search about it, is almost exclusively interested in splitting $\ce{H2O}$. However, looking at the Wikipedia article on electrolysis, it seems like it works for a bunch of ...
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Question about measurement of half-cell potential
I am reading about electrochemical cells from the chapter: Electrochemical cells, Batteries and Fuel cells in the book 'Physical Chemistry' by Thomas Engel and Philip Reid, 3rd edition.
I came across ...
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Why are moles (quantity of a gas) and temperature inversely related? [closed]
I'm learning about the combined gas law, and while doing calculations, I found that a doubling in the quantity of moles causes the temperature to be cut in half (all other things being equal).
I don't ...
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Sequential first order reaction graph in chemical kinetics
In graph given below is a sequential first order reaction
$$\ce{A ->[$k_1$] B ->[$k_2$] C}$$
For $k_2 \gg k_1$ the graph of concentration of $\ce{A}$, $\ce{B}$ and $\ce{C}$ is as follows.
Won't ...
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How to determine the surface reaction rate and equilibrium constant for a reaction between a solid site species and gas species
Consider the following reaction mechanism 1:
S1: $\ce{C-H (s) + H (g) <=> C^\star (s) + H2 (g)}$
S2: $\ce{C^\star (s) + H (g) => C-H (s)}$
S3: $\ce{C^\star (s) + C2H2 (g) => C-H (s) + H(g) ...
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Atomic terms and perturbation theory
I have a question about the derivation of the possible atomic terms of an atom. Consider an atom with $N$ electrons in the central-field approximation, with hamiltonian
$$
H_{0} = \sum_{i=1}^{N} \left[...
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Why is some first electron affinity endothermic [closed]
Elements like N and period 2 elements have endothermic EA. What's the explanation for that as isn't it usually exothermic?
Does this also imply that some elements subsequent EA is exothermic instead ...
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Franck-Condon principle and shift of wavelength
I was revisiting my notes for spectroscopy, and I came across the Franck-Condon-principle. I understand it well, but want to clear some doubts regarding this.
I know that the Franck-Condon-principle ...
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Why hot iron turns from red to white and then blue? [closed]
While reading structure of atom chapter no. 2 from ncert class 11th chemistry part 1 book, I got a doubt. In the book it says on page 40 that:
Hot objects emit electromagnetic radiations over a wide ...
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When adding a weak acid to a strong base in an acid-base titration, why does multiplying the pKa of the acid by two give the pH at neutralisation?
I'm not sure if the premise of the question is even correct, but when adding ethanoic acid to sodium hydroxide solution, I was told that the pH at the point of neutralisation should be around 2x the ...
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If Qc> Kc how can forward reaction can take place
If Qc>Kc then there will be a net backward reaction but still forward reaction will take place. My problem is if Qc>Kc forward reaction will become non spontaneous right. So how can that happen, ...
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What if kc=1 will reactants concentration equals to product concentration [closed]
I read a book, it says if kc=1 it mean reactant concentration equals to product concentration at equilibrium. But I'm wondering that in kc expression we dont just use concentration of an element we ...
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In a reversible reaction, how can endothermic and exothermic processes happen simultaneously?
A reversible reaction has both the forward and the backward reaction occurring at the same time. I struggle to understand how this is logically possible. One reaction pathway is always endothermic, ...
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Change of equilibrium constant with respect to temperature
Suppose we have an arbitrary chemical reaction $A+B\rightleftharpoons 2C+D$ and its equilibrium constant at two temperatures $T_{1},T_{2}$ are $k_{1},k_{2}$. We can relate them as
$$\log\frac{k_{2}}{...
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Jablonski diagram and absorption
I was reading about Jablonski diagrams and how they are structured. Bold lines would indicate ground electronic levels, and thin lines indicate the associated vibrational levels. Absorption only ...
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Approximate calculations of the product distribution under kinetic control
What is the product distribution when the energy difference between the transition states (∆TS = TS1 – TS2), is at 2 kcal/mol and when it is at 5 kcal/mol (assuming room temperature)?
I know that 1.4 ...
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Why are the derivatives of the concentrations divided by stoichiometric coefficients?
Consider this simple dioxygen to ozone chemical equation
$$\ce{3 O2 -> 2 O3}$$
with the average rate of the reaction
$$r = -\frac{1}{3}\frac{\Delta[\ce{O2}]}{\Delta t} = \frac{1}{2}\frac{\Delta[\ce{...
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Why does N,N-dimethylethanamide have a higher boiling point than butanoic acid?
According to Wikipedia, N,N-dimethylethanamide has a boiling point of $\pu{165.1 °C},$ while butanoic acid has a boiling point of $\pu{163.75 °C}.$
From what I learned, butanoic acid should have a ...
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Polyatomic molecule vibrational spectra - Molecular dipole expansion in Taylor series
To give some context: I am studying the molecular spectra in the context of an introductory course to atomic and molecular physics. My professor is using the transition rate expression from an initial ...
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Total bond dissociation temperature [closed]
I understand that covalent bonds break at a dissociation energy $D_0$ that is a function of the particular bond. And it looks like an upper bound on $D_0$ is known for possible covalent bonds.
It's ...
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