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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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Will a container made of ice hold an alcoholic beverage that is below freezing in an environment that is also below freezing? [closed]

This very specific question that came after saw I a travel episode where they served alcoholic beverages in ice glasses in an ice bar. I wondered if the drink contents would stay in the glass (of ice) ...
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2answers
877 views

Is there a physical explanation why benzene's pi molecular orbitals in a Frost circle are degenerate but pyridine's are not?

From here, the Frost Circles for both benzene and pyridine: The $\pi$-MOs formed by 6 $\pi$-AOs of an aromatic ring are: Listed with respect to the ordering in the above image, these MOs in benzene'...
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1answer
59 views

Molecular Geometry [duplicate]

Why is it that for a molecule with trigonal bipyramidal geometry, the lone pair is located in the equatorial region whereas for a molecular with an octahedral geometry, the lone pair is located in the ...
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1answer
203 views

Graphite: Thermal and electrical conductivity

I recently encounter this question: Compare, while providing an explanation, the thermal and electrical conductivity of graphite to that of diamond. Provided answer: Graphite conducts electricity(...
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0answers
72 views

Hückel method for biphenyl

I am trying to calculate the energy levels of biphenyl (see picture below) using Hückel method. Since this is my first time using Hückel I am a little confused. Biphenyl has 12 carbon atoms, ...
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1answer
92 views

Distinguish between two possible configurations for angular momentum in carbon atom

Consider the possible values of $S$ and $L$ for carbon configuration $1s^2 2s^2 2p^2$ and the corresponding rapresentations with arrows indicating the spins (consider only $S=0,L=0$ and $S=0,L=2$, as ...
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1answer
119 views

Why is the melting point of hydrogen fluoride lower than that of ammonia?

The melting point of hydrogen fluoride is -83.6°C, as compared to that of ammonia, which is -77.73°C. How does this make any sense? Both hydrogen fluoride and ammonia show hydrogen bonding, which "...
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1answer
75 views

In Bohr's model what is angular momentum in the lowest orbital?

Angular momentum is given by: $n\frac{h}{2\pi}$ where $n=1,2,3...$ And angular momentum is also given by: $\sqrt{l(l+1)}\frac{h}{2\pi}$ By the first equation angular momentum should be $\frac{h}{2\...
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0answers
27 views

Is H2O the only compound with a density anomaly? [duplicate]

My question is simple: are there any elements, compounds or materials other than water (H2O) which have a density anomaly characterized by a turning point in the τ-ρ curve?
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1answer
358 views

Relative molecular mass of an unknown gas in a mixture

A gaseous mixture contains oxygen and another unknown gas in the molar ratio of 4:1 diffuses through a porous plug into 245 seconds, under similar conditions same volume of oxygen takes 220 seconds to ...
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1answer
52 views

Is the stoichiometric coefficient equivalent to the mole fraction?

I have a small problem to understand (or distinguish between) two concepts of free mixing enthalpy. In several textbooks, I found the following formula for the molar free mixing enthalpy (binary ...
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0answers
71 views

distillation of aqueous CAN solution for the purpose of a reversible and strong endothermic reaction in cool packs

I know calcium ammonium nitrate (CAN) is used for cold packs. By bending a small metal plate the salt gets dissolved in water (separated pack) and this process is endothermic. I would like to heat ...
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0answers
99 views

The nature of Chemical Bonds [closed]

It was nearly a year ago when I appeared for my first interview through the KVPY (a research oriented scholarship exam) when one of the questions the panel asked me was : What is a chemical bond? ...
7
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1answer
115 views

Do molecules change shape when they become vibrationally excited?

In quantum mechanics we learn the the classical picture of a vibrational excitation is wrong. The atoms will 'vibrate' only while the molecule is in a coherent superposition of two vibrational states, ...
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1answer
94 views

“Proof” that the chemical potential is less than zero for irreversible material changes

From Levine's Physical Chemistry 6th edition: In a closed system, $\mathrm dG = -S\,\mathrm dT + V\,\mathrm dP$ not only applies to constant composition but also reversible changes in composition (...
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1answer
37 views

How can prepare ppb solution of sodium [closed]

How can prepare 1000ppb solution of sodium from sodium chloride salt in one litre.
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1answer
117 views

Coordination number of spheres (all identical) in hexagonal close packing (HCP)

I was revising solid state chapter when I came across this question What is the maximum coordination number of an atom in a hcp crystal structure of an element? The word 'maximum' drew my ...
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0answers
59 views

How to calculate a molecule's oscillator strength?

I was wondering how to calculate a molecule's (e.g. biphenyl) oscillator strength using a very simplified model. If I want to calculate a molecule's excited states a good start is something like a ...
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4answers
115 views

A simple equilibrium problem

Take the following simple equilibrium: $$\ce{CH3COOH + H2O <=> H3O+ + CH3COO-}$$ Ethanoic acid will act as a typical Brønsted-Lowry acid and donate a proton to water, forming a conjugate acid-...
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0answers
63 views

Calculation Radial distribution function using Potential

I am trying to understand an article where it is describing the accuracy of a potential function obtained via a NN (neural network). To test the ability of the NN potential to describe also ...
2
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1answer
72 views

Why are the concentrations in the equilibrium constant multiplied? [duplicate]

$$\alpha\,\mathrm{A}+\beta\,\mathrm{B}+\cdots\rightleftharpoons \rho\,\mathrm{R}+\sigma\,\mathrm{S}+\cdots$$ The equilibrium constant for this reaction can be calculated using the following formula: $...
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1answer
54 views

What does it mean for an equillibrium to move? [duplicate]

Le Chatelier's principle was described to me as: If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change. I do not understand ...
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1answer
60 views

Calculate force on atoms given the energy of configuration, trajectory of simulation and position of atoms in each frame

Background I am using a neural network to calculate the potential energy of atoms in a configuration and then adding energy of all atoms to compare it with the true energy of the configuration(label) ...
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2answers
59 views

Why do we use the word phase and state of matter so interchangeably? [closed]

I would be happy if someone explains me why the word "phase" and "state of matter" is used so interchangeably.Lets say we have HBr and another compound in the system both gases.Then am I to take two ...
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1answer
87 views

Why does the liquid in an Oralmedic stick flow uphill after I turn it upside-down?

I was experimenting with an Oralmedic stick, which is basically a cotton swab with a hollow stick that has liquid medicine inside, and observed something very unexpected. I followed the usage ...
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0answers
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Cell Potential of a cell with a reference electrode

In my textbook there is a question asking about the cell potential of a cell that has a reference electrode. It gives me the equation: $\ce {Ag_2CrO_4(s) + 2e^- -> 2Ag(s) + CrO_4^2-(aq)}$ and ...
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1answer
271 views

Why does ethane release more energy than ethyne when burned?

My book explains that since ethane contains a single bond, ethene contains a double bond, and ethyne contains a triple bond, and that when burned ethane releases the most energy because "the fact that ...
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0answers
58 views

How to calculate the enthalpy of fusion at a different temperature?

The heat capacity of liquid iodine is $80.7$ $\ce{J*K^{-1}*mol^{-1}}$, and its enthalpy of vaporization is $41.96$ kJ $\ce{*mol^{-1}}$ at its boiling point ($184.3$ $\ce{^oC}$). Furthermore, the ...
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1answer
666 views

Which formula can be used to calculate the exact hydronium concentration present in sodium hydrogen carbonate solution?

Which formula can be used to calculate the exact hydronium concentration present in sodium hydrogen carbonate solution ? $$\ce{[H3O+]}=\sqrt{K_\mathrm{a1}K_\mathrm{a2}}$$ $$[\ce{H3O+}]=\sqrt{\frac{...
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2answers
91 views

Why does the compound formed after a coordinate bond have a net charge? [closed]

Why does the molecule have net positive charge?
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0answers
71 views

Calculating excitation energies of a molecule

I am trying to calculate the excitation energies for the first three transitions of a molecule which is made up by a chain of k phenyl rings, where k shall be between 1 and 8. The angle between each ...
3
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1answer
99 views

Knowing that CI is variational for any basis set, why is coupled-cluster variational in the full correlation limit?

This is the question asked in Martin's comment to my answer to: Why is Coupled Cluster not variational? In the comment I was also asked to provide a publication as a reference:
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Mismatch in the trends of atomic size and atomic radius

In the periodic table, the atomic radius decreases as we move from left to right in a period. However, the atomic volume should also decrease as a result of the decrease in atomic radius, as volume is ...
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1answer
53 views

What is the relationship between emission and fluorescence?

A molecule exposed to a photon with some energy is put into an excited state, and emits a photon of some energy when it returns to ground state. The photon that provided the energy for excitation ...
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1answer
88 views

Notation for excited states

I am reading some papers about quantum chemistry and in one I found a notation for excited states of a molecule that I don't understand at all. In the picture below you can see the potential curves ...
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1answer
1k views

How to calculate n factor for O2 and H2 in this reaction? [closed]

How do I find n factor of $\ce{O2}$ and $\ce{H2}$ if I want to use equivalence principal on a reaction like $\ce{O_2 +2 H_2 -> 2 H2O}$?
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1answer
280 views

What happens to the methanol formed by the hydrolysis of methyl 2-hydroxybenzoate (oil of wintergreen) when synthesising salicylic acid?

Here are the reaction equations for reference (you may recognise this as a preliminary step for the synthesis of aspirin). Steps for synthesis of salicylic acid: 1) methyl 2-hydroxybenzoate + sodium ...
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1answer
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Is there a formula for density of any gaseous substance just based on its molar mass?

$\pu{112 ml}$ of hydrogen combines with $\pu{56 mL}$ of oxygen to form water. When $\pu{224 mL}$ of hydrogen is passed over heated cupric oxide, the cupric oxide loses $\pu{0.160 g}$ of its weight. ...
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2answers
148 views

What is the relationship between the constant of equilibrium (Kc) and the position of equilibrium? [duplicate]

I understand that the constant of equilibrium is a ratio of the concentration of the products to the reactants and that this value allows one to estimate whether the position of equilibrium lies to ...
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1answer
65 views

What is the molecularity of the RDS of a zero order complex reaction?

If we have a zero order complex reaction (although uncommon in chemical practices), say the decomposition of ammonia: $$\ce{2NH3 -> N2 + 3H2}$$ This is a zero order complex reaction. In my ...
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0answers
37 views

Absence of anti-Stokes line in Raman spectrum

If we have a molecule 1H-25X which shows a band at $3000~\mathrm{cm}^{-1}$ in the IR spectrum and you want to record a Stokes and anti-Stokes Raman spectrum with a laser of 1000 nm, why is the anti-...
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1answer
60 views

How can we measure the rate of reaction of EDTA chelation with zinc carbonate?

I am performing an experiment in order to find the activation energy of EDTA chelation. Consequently, I need to measure the rate of reaction of the process. I am high school student, and so I do not ...
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1answer
676 views

What is the effect of oxygen in welding?

Welders use a shielding gas to avoid oxygen interact with the electrode. I supposed is might be because of ferric oxide formation as the electrode is steel-made. But fusion temperature of ferric oxide ...
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0answers
41 views

How does association within vapor or dissociation within liquid affect the ideal nature of a binary solution?

As I understand, when there is positive deviation of a binary solution from Raoult's Law, the equilibrium partial pressure curve approach ideality (i.e a straight line dependence of equilibrium ...
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0answers
437 views

What are the differences between monotropic and enantiotropic polymorphic transformations?

I'm studying polymorphism and came across the terms "enantiotropic" and "monotropic" transformations. The first is described as reversible, whereas the latter, irreversible due to metastability. But ...
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1answer
83 views

What is the pH of this H2SO4 solution? [duplicate]

I'm trying to solve a simple problem which is driving me crazy. It says: Estimate the pH of a solution that contains 1 gram of $\ce{H_2SO_4}$ dissolved in 1 liter of water. When I solve the ...
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1answer
200 views

Finding equation of line of the P-T graph for a gas dissociation reaction

Gas A (1 mol) dissociates in a closed rigid container of volume 0.16 lit as per following reaction. $$\ce{2A (g) -> 3B (g) + 2C (g)}$$ If degree of dissociation of $\ce{A}$ is 0.4 and ...
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0answers
81 views

Calculate the density and enthalpy of an acid

Background: I routinely need to know the density and enthalpy of water at elevated temperatures and pressures and I use the NIST steam tables to do this. https://www.nist.gov/publications/steam-tables ...
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Ionization energy in Geiger counters

Geiger counters can detect radioactivity because nuclear radiation consists of particles or radiation of sufficiently high energy to eject electrons from atoms. Consequently, this type of radiation is ...
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Why do ions form condensation centres in isopropanol vapour?

In cloud chambers the particles are detected when a particle passes through the chamber causing the vapour to condense into a "cloud". What Process causes this observed phenomenon? In other words, how ...