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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247 views

Calculating partial pressure of carbon monoxide

$\ce{ZnO}$ is exposed to pure $\ce{CO}$ at $\pu{1300 K}$ and the equilibrium $$\ce{ZnO(s) + CO(g) <=> Zn(g) + CO2(g)}$$ is then established at $\pu{1 atm}$ pressure. The density of the ...
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1answer
62 views

What is the interaction between dissolved ions of opposite valence in a solution at rest?

NaCl is dissolved in water. Ions sodium and chloride are sufficiently free from each other so that they may occupy different regions of the solution after an active transport process through a ...
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36 views

What is the effect of applied magnetic field on absorption spectrum?

Upon application of a weak magnetic field, a line in the microwave absorption spectrum of rigid rotor splits into $3$ lines. The quantum number $(J)$ of the rotational energy level from which the ...
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3answers
88 views

Is enthalpy of combustion the 'heat released' or 'enthalpy change'?

In a constant volume calorimeter, $\pu{3.5 g}$ of a gas with molar weight $\pu{28 g}$ was burnt in excess $\ce{O2}$ at $\pu{298 K}.$ Temperature of calorimeter increased from $298$ to $\pu{298.45 K}$ ...
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33 views

Can I use the quasi-equilibrium approximation when drug and ligand distribution volumes are different?

A drug $D$ binds a ligand $L$ to form a complex $C$ according to the law of mass action. Furthermore, mass balance should be achieved. Can I still assume quasi-equilibrium when the distribution ...
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2answers
103 views

How is energy not stored in bonds? [duplicate]

Consider the paraphrase from Ebbing: It takes energy to break bonds & energy is released when bonds are formed Let's look at the first statement It takes energy to break bonds. Is this true ...
4
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1answer
89 views

Is it really possible for a liquid to stay afloat a gas (vapor)?

I have a book at home called Chemical Thermodynamics for Process Simulation (I have the first edition) and at the very beginning of chapter 2 of the book one may read the following: No reference is ...
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2answers
456 views

Phenolphthalein Indicator mixed with base that first turns pink and then clear

What occurs in the following situation: After adding 2 drops of Phenolphthalein Indicator (an indicator that turns bases pink and stays clear for acids,) into a unknown solution, the solution turns ...
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1answer
57 views

Why does an electron lose energy so that it falls back to a lower energy state than just stay at the higher energy state?

Suppose an electron in the 2nd shell gets excited and jumps to the 4th shell. Shouldn't the electron then exist in an unstable equilibrium in the 4th shell, than lose energy and drop down to the 2nd ...
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1answer
66 views

Heat exchange in adiabatic process

I know my teacher told me that In adiabatic process there is no exchange for heat between system and surrounding. Then he came to point. From first law of thermodynamics $$∆U = q + W \tag{1}$$ ...
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54 views

Electric fields in a galvanic cell

I have read hat there is two types of electric fields exist in galvanic cell.I understand E because of charges accumulated on electrodes but what about other E -field? What does cause this field and ...
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44 views

How to achieve Löwdin transformation?

I use Gaussian 09 to obtain the Hamiltonian and overlap matrices, $H_0$ and $S_0,$ where the B3LYP functional and the 6-31G basis set are adopted. Then how to transform the system to an orthogonal ...
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49 views

Why is $E°_{cell}$ not $\Delta E°_{cell}$?

$E°_{cell}$ is the EMF of the cell for a reaction with respect to standard hydrogen electrode(SHE). So why don't we represent $E°_{cell}$ or $E_{cell}$ by $\Delta$ symbol, in the same manner in which ...
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1answer
80 views

How strong are molecular bonds in layman's terms?

Suppose you had a single sheet of graphite the size of an A4 page. What would it feel like to handle it? Would your fingers instantly tear through it as you tried to grasp it? Could you punch your ...
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202 views

What is the purpose of phase matching when drawing a MO diagram?

During the lecture, we were learning how to draw the MO diagram for $\mathrm{BF_3}$. I understand that only orbitals with the same symmetry labels can interact and form molecular orbitals. My ...
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1answer
38 views

Explain me concept of vapour pressure like I am five [closed]

I have browsed internet to understand the concept of vapour pressure but something isn't linking for me. How do we relate vapour pressure to temperature for liquid only and any simplified definition ...
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2answers
663 views

d-Menthol vs dl-menthol: Does an enantiomer and its racemic mixture have different melting points?

I am checking out Wikipedia and it shows a different melting point (m.p.) for l-menthol $(\pu{42 ^\circ C}$ to $\pu{45 ^\circ C})$ vs dl-menthol $(\pu{36 ^\circ C}$ to $\pu{38 ^\circ C}).$ How is ...
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71 views

Chemical Kinetics regarding Iodination of Cyclohexanone

We did an experiment to determine the overall order of iodination of cyclohexanone. Rate of a certain chemical reaction = $\ce{k[A]^p[B]^q[C]^r}$ so the overall order = p+q+r We're referring to a ...
2
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2answers
183 views

Why does the dipole moment of molecules go from positive to negative? [duplicate]

In physics the dipole moment is said to go from the negative to the positive pole, check for instance https://en.wikipedia.org/wiki/Electric_dipole_moment (Elementary definition). This makes sense ...
2
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1answer
156 views

Ratio of uncharged to charged side chains [closed]

The $\mathrm{p}K_\mathrm{a}$ of the side chain imidazole group of histidine is $6.0.$ What is the ratio of uncharged to charged side chains at $\mathrm{pH}~7?$ Here's my attempt to the solution: $$7 ...
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1answer
409 views

Chemical kinetics

Consider a reversible reaction $\ce{A}$ converts to $\ce{B}$ and $\ce{B}$ converts to $\ce{A}$ with forward and backward rate constants $k_\mathrm{fwd} = k_\mathrm{rev }= \pu{1 s-1}.$ Suppose we start ...
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2answers
125 views

Is “density per unit volume” something?

I was reading articles on the preparation of shellac-based composites when I encountered the following statement (in ref. 1): Wood flour and fibres are interesting because of their low cost, good ...
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54 views

Is there any publicly available software that can do deterministic CCSDTQP other than MRCC?

MRCC can do arbitrary order coupled cluster but much of the code is computer-generated (not hand-coded by a human) so it can be slow. There are some stochastic codes for high-order coupled cluster, ...
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1answer
51 views

Can someone walk me through this gas mixture question?

Argon $(\ce{Ar})$ and helium $(\ce{He})$ are initially in separate compartments of a container at $\pu{25 °C}.$ The $\ce{Ar}$ in compartment A which has a volume $V_\ce{A}$ of $\pu{9.00 L}$ and a ...
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1answer
115 views

Isothermal vs adiabatic compression of an ideal gas [closed]

Could someone please explain these specific questions physically (especially the first question!)? I understand the corresponding mathematical proofs, but not the physical reasoning? I have looked ...
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1answer
44 views

When to use chromatographic separation vs vacuum-assisted rectification distillation?

I'm trying to understand a bit more about industrial scale separation processes. One particular element I'm interested in is the question as to when chromatography (HPLC or Simulated Moving Bed) may ...
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2answers
240 views

Equilibrium Constant & Rate-Determining Step

My first language is not English, so there might be some parts where it's hard to read. Sorry in advance. I have some questions regarding the derivation of the equilibrium constant and the rate-...
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0answers
27 views

Properties that probe electron kinetic energy

This post is inspired by a question regarding the meaning of off-diagonal elements of the KE matrix (in some AO basis). One answer suggests that a diagonalized KE matrix might not be very useful. I ...
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0answers
50 views

Explosive reaction based on reaction rate

Question We have the following chemical reactions: $$ \begin{align} \ce{A + B^* &-> C + D^*}\tag{1}\\ \ce{D^* &-> B^* + B^*}\tag{2}\\ \ce{B^* &-> B}\tag{3} \end{align} $$ ...
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37 views

Water replacement for pressure-testing [closed]

Due to circumstance, our Data Centre build has some delays and it currently looks like we're going to have to perform a hydrostatic test of our sprinkler system with live computers in it. As I have ...
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1answer
111 views

Mathematical justification for Le Chatelier's principle

At equilibrium $$ \begin{align} K &= \exp\left(\cfrac{TΔS^\circ - ΔH^\circ}{RT}\right)\\ ⇒ \frac{\mathrm d \ln K}{\mathrm dT} &= \frac{ΔH^\circ}{RT^2} \end{align} $$ If enthalpy change is ...
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1answer
54 views

why does adding a non volatile solute not decrease the boiling point?

If I add a solute that decreases the bond strength of the pure solvent then wouldn't the solvent molecules evaporate more easily as it has lesser force holding it down now?But in my textbook, it's ...
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1answer
115 views

What element has good conductivity but is also brittle? [closed]

I'm confused by what element(s) can be identified to have these properties. The following is text from my 2019-2020 Kaplan MCAT General Chemistry book under the metalloids section Silicon (Si) has ...
3
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1answer
69 views

How is the ln k term in the linearised Arrhenius equation acceptable?

In my syllabus we only study about rate laws under the topic "Rates of reactions", but as I was interested in it, I started to search about that topic. And then I found the Arrhenius equation $$\ln k ...
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1answer
118 views

Calculation of VOCs concentration (ppm) in the headspace of a bottle

What is the right way to calculate the concentration of volatile compounds in the air in a closed container? Suppose we have a $\pu{50 mL}$ bottle with $\pu{25 mL}$ of $100\%$ ethanol $(\ce{EtOH})$ ...
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2answers
150 views

Why is vapour pressure not dependent on shape and size of the container?

In my textbook, it's written that vapour pressure of a liquid does not depend on shape and size of a container but won't a container that provides less surface area to the liquid will have lower ...
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1answer
115 views

How to find the Cp, difference of Cp and heat of fusion from the dependence of vapor pressure on temperature?

The vapor pressure of zinc varies with temperature as $$\log P(\pu{mm Hg}) = -6850/T - 0.755\log T + 11.24 \label{eqn:1}\tag{1}$$ and that of liquid zinc as $$\log P(\pu{mm Hg}) = -6620/...
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102 views

How to I find the equilibrium temperature in this problem?

From Castellan's Physical Chemistry, chapter 12 [1, p. 276]: 12.18 At $\pu{25 °C}$ we have for rhombic sulfur: $ΔG_\mathrm{f}^\circ = 0,$ $ΔS^\circ = \pu{31.88 ± 0.17 J K-1 mol-1};$ and for ...
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1answer
189 views

Does CO2 form carbonic acid in the atmosphere?

Since when $\ce{CO2}$ goes into water it makes carbonic acid, then what happens when it rains? Some of the $\ce{CO2}$ in the air joins the rain drop as it falls and while the rain drop falls and ...
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1answer
68 views

Using molecular orbital for determining leaving group trend and nucleophilicity

Here is the question. Which one has better leaving group, cyclohexanol or cyclohexane that has $\ce{OH_{2}^{+}}$ substituent? Explain. I know the answer is the latter because if both compounds are ...
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0answers
38 views

What does “orthorhombic” actually mean?

I'm trying to understand what it means for a molecule to have orthorhombic symmetry. According to Di Lauro's "Rotational Structure in Molecular Infrared Spectra," a molecule is orthorhombic if the ...
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1answer
33 views

Separate less volatile component from distilling a mixture [closed]

Is it a strict rule that when we boil a mixture of two liquids, with one being less volatile than the other, the more volatile vapour has to form the greater portion of the total vapours? If it is so,...
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0answers
43 views

Psi4 gradient calculation with complete basis set? [closed]

I'm trying to set up a gradient calculation for psi4. In my input.dat file, I have tried the following keywords: set basis cc-pVTZ gradient('CCSD(T)') which is ...
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35 views

Obtaining conformational energy from Newman projections in first place

In this source, the conformational energy from Newman projections is obtained. Is there a formula or quantum chemistry approach to obtain the values in first place (pretend that I don't know the ...
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1answer
70 views

Why are the phase diagrams showing $G_s$ and $G_l$ situated so close on one end and then widens up at the other extremes? [closed]

With reference to the phase diagrams drawn in b and d why are the Gibbs phase lines coming closer from being so further apart?
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1answer
81 views

Equivalent mass in case of disproportionation reaction

I came across a question where the equivalent mass of hypophosphorus acid is to be found in the given reaction: $$\ce{2H3\overset{+1}{P}O2 -> H3\overset{+5}{P}O4 + \overset{-3}{P}H3}$$ If $M$ is ...
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1answer
28 views

Collision that governs kinetic model of gas [closed]

From Atkins' Physical Chemistry 10th, it states that The kinetic model is based on three assumptions: The gas consists of molecules of mass $m$ in ceaseless random motion obeying the laws ...
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0answers
36 views

Bond Dissociation Energy in Water [duplicate]

Why do the bond dissociation energies of the O−H bonds in water differ? Is it related to an increase in lone pair-bond pair repulsions upon the breaking of the first O−H bond (decrease in stability, ...
1
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1answer
148 views

Units of the rate constant for reactions whose order is greater than 1

In many textbooks, it is written that: The value of rate constant depends on the nature of the reactants, temperature and catalyst. It is independent of the concentration of the reactants. However,...
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1answer
43 views

What is the the total heat extracted in the process? [closed]

Since this is a cyclic process:- Change in internal energy=0. In the process C-A the work done W is zero, thus the heat Q is zero since it is an isochoric process. Next in the process A-B, I got the ...

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