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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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5 views

Intuition for the overlap integral

I want to ask a question about the overlap integral. I was studying about the MO diagram of $\ce{H_2^+}$ and we managed to derive an expression which had the following term: $$\ce{<1S_A(r_A) | ...
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3answers
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Effect of dilution on the degree of dissociation of an electrolyte

My book says that on dilution, the degree of dissociation of an electrolyte increases. Consider the reaction: $$\ce{A <=> C + D}$$ Let $\ce{A}$ be the electrolyte that splits into its ions $\...
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Moving water vapour between flasks

I have a flask of silica gel connected to a flask that contains a bit of water, so when I heat the silica gel the water absorbed gets evaporated and I want it to move to the other flask, but it always ...
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rate of reaction of the following reaction is 1.5 mol lit-1 sec-1 we have to find the consumption of reactants and formayion of product? [on hold]

I cannot find the consumption of reactants and formation of product please answer my question?
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Gibbs free energy of phosphorus pentachloride decomposition reaction

The equilibrium constant at $\pu{227 °C}$ for the equation $$\ce{PCl5(g) <=> PCl3(g) + Cl2(g)}$$ is $K_p = \pu{4.50E3 bar}.$ Calculate the value of $Δ_\mathrm{rxn}G^\circ$ at $\pu{227 ...
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62 views

Real Gas Behaviour

For a fixed amount of a real gas when a graph of $Z$ vs $P$ was plotted, then at a very high pressure slope was observed to be $\pu{0.01 atm^-1}.$ At the same temperature and pressure if a graph is ...
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1answer
97 views

Heat involved in isenthalpic process

Question 28 from [1, p. 4.4]: An ideal gas is expanded irreversibly from $\pu{5 L}$ to $\pu{10 L}$ against a constant external pressure of $\pu{1 bar}.$ The value of heat involved $(q)$ in this ...
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“Cold Boiling” and its physico-chemical basis and applications [on hold]

I need some information about "Cold Boiling" and its Physico-chemical basis and application in dissolving organic materials such as biofilms, pus and so on.
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2answers
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Clarification on the Clausius inequality

In Atkins' Physical Chemistry the criteria for spontaneity using Gibbs energy was calculated using the Clausius inequality: $$\mathrm dS ≥ \frac{\mathrm dq}{T},$$ and at constant pressure, $\mathrm ...
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1answer
54 views

Thermodynamic statements [on hold]

Question 13 from [1, p. 4.2]: Which of the following statements is true? (a) An ideal gas always obeys the equation: $PV^γ = \mathrm{constant}$ in adiabatic process. (b) An ideal gas ...
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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
49 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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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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1answer
38 views

Where am I wrong in the concentration potential calculation? [on hold]

With regard to concentration cells I have seen $E^\circ_\mathrm{cell}$ being calculated to be zero. However we have had this notion that $$E^\circ_\mathrm{cell} = E^\circ_\text{cathode(reduction)} - ...
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3answers
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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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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
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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 ...
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Does the enthalpy of neutralization depend upon the nature of strong acid and strong base? [closed]

In the book it's written that if the acid is dibasic then the enthalpy of neutralization will be 27.4 kcal but then at some other place it is written that it is independent of the nature of strong ...
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Least/Lowest London Dispersion Force! [closed]

What/Which would be the least London Dispersion Force? In the human body. And How many eV would it be?
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Thermodynamic Chemistry [closed]

my question is asking to calculate partial pressure of gas components for 2NO + O2 --> 2NO2 I have deltaH data, deltaS and Cp(standard) for each component... How do I calculate partial pressures of ...
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1answer
74 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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Photocatalytic process [closed]

Photocatalytic process was helped out in degradation of pollutant in water bodies and it will produce water and carbon dioxide as end product. Actually I think carbon dioxide will also pollute the ...
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I don't understand how hydration enthalpy is working for Cu+2 and Ni+2 [closed]

Even though Ni+2 has same hydration enthalpy as Cu+2 still Cu+2 has +reduction potential whereas Ni has negative
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2answers
37 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
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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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Why is Cu+1 less stable than Cu+2? Shouldn't it be the other way around? [duplicate]

After all in +1 state all the d orbitals degenerates are completely filled but in +2 only 4 degenerates are paired, there is an unpaired electron.
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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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What does it mean when we say Gibbs free energy in standard state?

I have heard my professor mentioning that standard Gibbs free energy has to do with constant pressure and has nothing to do with constant temperature. However in Ellingham diagrams in particular I ...
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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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32 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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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
78 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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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
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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
342 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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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 ...
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2answers
94 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 ...
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1answer
52 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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341 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
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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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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
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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
33 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
24 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
109 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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Does UV and Visible Light affects the Core electron, Valence electron, or Both?

When exposed in UV or Visible Light radiation, matter is induced to perform electronic excitation. Is the electron that excites, a core electron, a valence electron or can they both be excited? ...
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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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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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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 ...
2
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1answer
94 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 ...