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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Mismatch of coefficients in rate law expression

For example, for the reaction $\ce{A + 2B -> C}$, we have $$\text{rate} = -\frac{1}{2}\frac{\mathrm d[\ce{B}]}{\mathrm dt} \quad \text{and} \quad \text{rate} = k[\ce{A}]^x[\ce{B}]^y.$$ Together, ...
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Oscillator strength of a transition

I am trying to compute the oscillator strength in a molecule. Therefore I've got its Energy level values plus both wave functions $\Psi_i$ and $\Psi_j$ for the transition I want to calculate the ...
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If dG is a state function, why do reversible and irreversible paths differ?

For a reversible process at constant T,P in a closed system with no non-expansion work dG = 0. For an irreversible process under the same conditions, dG < 0. Since dG is a state function I would ...
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Atkins' Physical Chemistry 10th edition Question on steady-state approximation

Please help me with Example 20E.2 of Atkins' Physical Chemistry 10th edition textbook on using the steady-state approximation. I have attached my attempt but am just not sure how to get to the final ...
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Time until completion for $n$-th order reaction

For an $n$-th order reaction, how to determine the time until all the reactants run out? My approach is the following. The reaction kinetics is modeled by the differential equation $$\frac{\mathrm d[...
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205 views

How to verify if a rate law fits the experimental data?

A student after doing an experiment on chemical kinetics, decided that the rate law of the reaction is $u = k[\ce{IO3-}]$ which is correct, but do the data below match with this? Or does he have to ...
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95 views

Can anyone explain this condensation pattern?

What is the hair-like polymer that condenses on the caps of the plastic cell vial? Inside vial are cells in a mixture of FBS and DMSO. The vials were frozen slowly in a special isopropanol-filled ...
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121 views

Brillouin zones of a compound after structural relaxation

My background in solid-state chemistry isn't much, so I apologize in advance if there arises the need to raise a basic fact while answering my question. I've been learning mostly from the web, with my ...
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Is order of reaction defined for nuclear reactions?

I am asking this question after asking a similar one for spontaneous nuclear decay phy.stack. Link Order of reaction is defined for chemical reaction. But wikipedia says about spontaneous nuclear ...
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reaction between Green tea and sodium bicarbonate

There is a tea in northern Pakistan called noon chai or Kashmiri chai. It is distinct between it is a pink colour. The method involves brewing green tea leaves in cold water and adding sodium ...
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133 views

Is there a physical explanation behind the derivation of spectroscopic term symbols?

In deriving the spectroscopic term symbols, one method seems common among several sources, the clearest presentation for me being located here, a derivation of the term symbols for a $d^2$ ion. So, ...
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261 views

Hammett plot shape: dependent on substituent or mechanism?

So, we were shown a Hammett plot that, on the left was linear, but on the right was concave up. How would I explain the shape of the Hammett plot? Does it depend on whether the substituent is an EDG ...
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172 views

Stability of unsaturated syn/anti 3-ladderane

In an oral exam for physical organic chemistry, one student was asked to explain the differences in the ionization potential ($IP$) of syn and anti tricyclo[$4.2.0.0^{2,5}$]octa-3,7-diene (unsaturated ...
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907 views

Why does diamagnetic current induce a downfield while the paramagnetic current induces an upfield shift?

I know that aromatic rings exhibit diamagnetic ring currents which causes the protons outside the ring to go downfield in H-NMR. Antiaromatic compounds exhibit paramagnetic ring currents which have ...
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Computing van der Waals constants from molecular structure

How can van der Waals constants be computed from molecular structure? Is there software that already does this? Is there software that can design a molecule with specified van der Waals constants? ...
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234 views

Howcome orbitals become 'core-like' when electrons are removed?

It seems to me that f-orbitals for lanthanide metals are treated as 'core-like' when a certain number of electrons have been removed. Or, as Radiochemistry puts it, The 4f binding energy is so ...
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Could we bond hydrogen to the edges of covalent network structures like diamond?

I know that diamond is just carbon atoms structured in a way that differs from graphite and charcoal. The carbon atoms on the edges do not have full valence shells. Would it be possible to attach ...
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Tools for investigating hydrogen bonding

What would be the best tool to investigate local molecular organization in liquid mixtures due to hydrogen bonding? For example, I might want to look at how water molecules hydrogen bond to PNIPAM vs ...
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Glycine nucleation simulations

I am trying to run nucleation simulations of glycine in water. To generate a supersaturated solution, a solution that will crystallize, I need to know the solubility. Luckily for me, this data exists. ...
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Problem with partition function when calculating equlibrium constant?

For example a reaction is given as ($\pu{T = 1000 K}$), $$\ce{2Na(g) <--> Na2 (g)}$$ The equilibrium constant, $$\ce{K_{c} = \frac{\frac{q_{Na_{2}}}{V}}{(\frac{q_{Na}}{V})^2}}$$ But when ...
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Why do we assume that the successive deprotonation of a polyprotic acid happens when only the previous deprotonation has reached equilibrium?

The steps for finding the concentration of the species at the equilibrium of polyprotic acid are as given in this book in section $10.16$ and illustrated on the next page. I have three questions, but ...
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The Mechanism of Termolecular Reactions

How does a termolecular elementary reaction happen under the law of mass action? My physical chemistry textbook only says details about bimolecular and unimolecular reactions with collision theory. I ...
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50 views

Is dehydration of cobalt(II) chloride hexahydrate dynamic equilibrium?

I know that the dehydration of cobalt(II) chloride hexahydrate is a reversible reaction, is it a dynamic equilibrium? $$ \begin{align} \ce{CoCl2·6H2O &<=> CoCl2·2H2O + 4 H2O}\tag{R1}\\ \ce{...
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Why aren't electrons included in the equilibrium constant expression?

This might be elementary, but why aren't electrons included in the equilibrium constant for a half-reaction? For example, for $$\ce{O2 (g) + 4H+ (aq) + 4e- -> 2H2O(l)}$$ we have $$Q = \frac{(a_\ce{...
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Is there a parameter for degree of ‘mixedness’

So I was making coffee this morning and when mixing some milk into the black coffee, I wondered if there was some parameter or value in chemistry which describes how well mixed two liquids (or gases) ...
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Steady state approximation for three-step cycle

How to write the steady state for $\ce{A}?$ $$\ce{A ->[$k_1$] B ->[$k_2$] C ->[$k_3$] A}$$ Species $\ce{A}$ seems to appear on both side of equation as it uses itself to produce some of ...
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32 views

Debye–Waller factors for tin(IV) oxide

How I could find the bulk Debye–Waller factor for tetragonal rutile type $\ce{SnO2}$ at room temperature? I have been doing some online digging with no luck. If anyone has a reference I could use that ...
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62 views

Practical meaning of omega potential

In statistical thermodynamics, the quantity omega potential is defined and is different for fermions, photons, phonons and other particles . I have been understanding the derivations of omega ...
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113 views

Calculating the ionic strength of a histidine solution

I'm trying to repeat the calculation of the ionic strength of a solution containing histidine as a buffer I recently read in a paper. In their paper, the authors calculate the ionic strength of a 20 ...
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65 views

What is the difference between sublimation and instantaneous fusion+vaporisation?

Sublimation is defined by the IUPAC as The direct transition of a solid to a vapour without passing through a liquid phase. A sublimation equilibrium can occur in two sets of conditions: at a ...
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What is a possible conventional interpretation of Wilfred Hagen's puzzling Electron Paramagnetic Resonance spectrum?

In searching for a conventional interpretation, Wilfred Hagen of Delft Technical University is stumped by an Electron Paramagnetic Resonance spectrum (aka Electron Spin Resonance spectrum) in "...
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Is standard change in activation Gibbs free energy indepedent of pressure?

For a chemical reaction the activation volume is defined as: $$Δ^{\ddagger}V={V^\ddagger}-V$$ where both $V^\ddagger$ and $V$ refer to standard states (I have omitted the symbol for simplicity). One ...
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How to find the equilibrium constant under non-standard conditions?

Given the following thermodynamic data at $\pu{298 K}:$ $$ \begin{array}{lrrr} \hline \text{Compound} & \Delta_\mathrm{f}H^\circ/\pu{kJ mol^-1} & S^\circ/\pu{J K^-1 mol^-1} & C_p^\circ/\pu{...
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Relationship between molecularity and the reaction order

Should the molecularity be equal or less than the reaction order? Consider the reaction: $$\ce{H2(g) + I2(g) → 2 HI(g)}$$ If we consider the mechanism of this multi-step reaction, the molecularity is ...
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Why would T1 relaxation time change ~20 fold between solvents for the same substance?

I have a simple, completely conjugated pyridinium salt with MW of ~300 g/mol. The molecule consists of regular non-labeled atoms (only C, H, N). If the 1H T1 relaxation time for this molecule is ...
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102 views

(Probabilistic) entropy associated with many equally probable microstates

This is a pretty naive question. The probabilistic definition of entropy is (for a mole of particles) $$-R\sum_i p_i\ln p_i $$ in which $p_i$ is the probability of a given microstate and $\sum p_i =1, ...
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Correlating specific heat (Cp) of a substance with other substance on the basis of similar physio-chemical properties

I am modelling $\ce{H2O2}$ decomposition in ANSYS Chemkin-Pro and I have difficulty finding $C_p$ (specific heat at constant pressure) for liquid $\ce{H2O2}$ for various temperature ranges. My ...
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Deriving an expression from Navier-Stokes under creeping flow

So I'm trying to derive $$\mu\nabla^2\vec{v}=\nabla P-\rho g$$ from Navier-Stokes equation $$\begin{align}\rho \left(\frac{\partial\vec{v}}{\partial t}+\vec{v}\cdot(\nabla\vec{v})\right)&=\rho\vec{...
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Artificial Muscle | HASEL's Reaction

I was watching a TED-talk on artificial muscle, HASEL, where the inventor demos that an insulated oil in the presence of electric potential field gets displaced due to Maxwell stress inside oil. ...
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Mechanism of decomposition of alkali metal halides in flames

A student recently asked an interesting question What happens when KCl is introduced in the Bunsen flame?. This apparently simply question led me to an interesting debate. We all know that emission of ...
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569 views

Number of moles of acidified potassium dichromate required to liberate 6 moles of iodine from an aqueous solution of iodate ions

I came across this question in a recent exam I had taken: How many moles of acidified $\ce{K2Cr2O7}$ is required to liberate 6 moles of $\ce{I2}$ from an aqueous solution of $\ce{I-}$ ? So this is ...
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Why does high blood gas partition coefficient of a inhalational anaesthetic drug mean slower induction of anesthesia?

High blood gas partition coefficient of a drug corresponds to higher solubility of the drug in blood leading to high concentration of the drug in blood with respect to gas (air in alveoli). If the ...
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Generating hybrid atomic orbitals for Boron

My professor was showing us how to form hybrid atomic orbitals for Boron by taking a linear combination of rotated 2p orbitals and 2s orbitals (of Boron). This was done in a particular manner such ...
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Intuition behind errors

I want to ask a question about the multiplication of two variables and the error associated with the process. I was learning about calculating errors in the physical labs at school and was taught ...
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164 views

Why does Larmor precession occur in NMR?

Larmor precession is the phenomenon that in NMR the spin (and by default also the magnetic dipole moment) of protons does not line up with the applied magnetic field but rather precesses around this ...
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225 views

Is the active mass of every solid and liquid taken to be unity?

I learnt from my textbook and the question/answer - Why is active mass of a pure solid or liquid always taken as unity? that active mass of a solid or liquid is taken to be unity as: $$[A]=\frac n V=\...
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107 views

Why does the electrical conductivity increase as the temperature decreases?

I am measuring the dependence of electrical conductivity of ( NaCl and $\ce{CH3COONa}$ solutions with concentration 9g/L) with temperature using conductivity meter. Theoretically the conductivity ...
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Rate constants and their relationship to quantum yields

Question A dye molecule has a singlet excited state lifetime of $\pu{0.85 ns}.$ The quantum yield of triplet formation is $35~\%.$ What is the rate constant for intersystem crossing from the ...
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96 views

Is it possible to have a negative overall activation energy for a whole reaction mechanism?

I am trying to find out correlation for ignition delay for alkane fuels. The activation energy part of the correlation gives me a negative value. For the ignition delay formulation, is it possible to ...
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111 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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