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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43k views

Why is the enthalpy change not zero in an adiabatic process?

Which of the following must be true for adiabatic processes? $C_V = C_p$ $\Delta H = 0$ $\Delta U = 0$ $\Delta S = 0$ $q = 0$ (Source: Chemistry GRE) The answer is $q = 0$. From ...
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1answer
50 views

Are viscoelastic materials to be considered solids or fluids?

I recently stumbled upon the concept of viscoelasticity. Not being a chemist, but being interested in the topic, I started to read the wikipedia article. The main thing I extracted from it is: ...
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1answer
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Why is Kc not affected by change in pressure?

Why is $K_c$ not affected by change in pressure? I know the mathematical explanation, but I don't really understand the reason when only looking at $K_c$. The explanation I know is with the reference ...
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1answer
30 views

Where am I wrong in the concentration potential calculation?

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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2answers
31 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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3answers
57 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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0answers
28 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
44 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 ...
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11 views

Does the enthalpy of neutralization depend upon the nature of strong acid and strong base? [on hold]

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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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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38 views

Least/Lowest London Dispersion Force! [on hold]

What/Which would be the least London Dispersion Force? In the human body. And How many eV would it be?
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0answers
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Thermodynamic Chemistry [on hold]

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
69 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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0answers
44 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
131 views

Enthalpy change of gas expansion against constant external pressure

A certain mass of gas is expanded from $\pu{1 L}$ at $\pu{10 atm}$ to $\pu{4L}$ at $\pu{5 atm}$ against a constant external pressure of $\pu{1 atm}$. If initial temperature of gas is $\pu{300 K}$ and ...
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0answers
13 views

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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1answer
41 views

What is reversible work? [closed]

I am not getting the intuition behind reversible work? What exactly is reversible work? What does it mean when someone says that in reversible work can be reversed by an infinitesimal amount at any ...
0
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1answer
39 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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0answers
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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
5
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1answer
340 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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0answers
22 views

Olympiad ICHO question [closed]

Can anyone please help me with this question(https://i.stack.imgur.com/p7ppK.jpg)
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1answer
71 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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0answers
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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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1answer
40 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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1answer
87 views

Gravimetric analysis

In a gravimetric determination of phosphorus an aqueous solution of dihydrogen phosphate ion is treated with the mixture of ammonium and magnesium ions to precipitate magnesium Ammonium Phosphate. ...
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0answers
27 views

For the purposes of auto racing, I am a Nascar driver trying to design a solution for heat exposure [closed]

Question, is it possible to pump liquid through some type of specially designed cool shirt without fluid coming in and out of the shirt, but rather just circulating and cause a chemical reaction to ...
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4answers
5k views

Does a catalyst increase atom economy?

Somebody I know insists that the use of a catalyst increases the atom economy. They did chemistry at school and were told that a catalyst increases the atom economy. He pointed me to several past ...
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0answers
20 views

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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0answers
16 views

How does the initial starting temperature affect yield? [closed]

I am aware that using Le Chatelier's principle, increasing the temperature of a system (exothermic reaction) at equilibrium decreases yield as it causes a net reverse reaction. However, I would like ...
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0answers
36 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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1answer
604 views

Electrochemical Cell

Now in an electrochemical cell , we make use of the fact that whenever there is a potential drop , electrons will flow from lower to higher potential as for a potential drop , there must be an ...
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6answers
460k views

Positive or Negative Anode/Cathode in Electrolytic/Galvanic Cell

In a galvanic (voltaic) cell, the anode is considered negative and the cathode is considered positive. This seems reasonable as the anode is the source of electrons and cathode is where the electrons ...
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0answers
19 views

Barrier inversion of phosphites [closed]

What is inversion barrier of trimethyl phosphite, triethyl phosphite, triisopropyl phosphite and triphenyl phosphite and whether they interconvert via T-shaped geometry?
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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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3answers
15k views

Calculate the standard oxidation potential from given potentials

The standard electrode potentials for the following redox couples are given as: >$E_0(\ce{Fe^{2+}/Fe}) = x~\mathrm{V}$ and $ E_0(\ce{Fe^{3+}/Fe^{2+}}) = y~\mathrm{V}$ What will be potential $E_0(\ce{...
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2answers
93 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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2answers
319 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 ...
2
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0answers
48 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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0answers
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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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0answers
44 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
31 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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0answers
36 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 ...
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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 ...
4
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2answers
106 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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2answers
119 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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1answer
213 views

What “physical method” does Feynman refer to in The Feynman Lectures on Physics (Vol 1)

In the introductory chapter, Atoms in Motion, of the Feynman Lectures on Physics (Volume One), Feynman alludes to a certain "physical method", which can be used to determine the structure of α-iron (...
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1answer
50 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 ...
3
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1answer
32 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 ...
0
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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 ...
9
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3answers
3k views

How to explain the discrepancy between the calculated absorption wavelength within the particle in the box theory and the observed wavelength?

The experimental observed wavelength for this molecule is 425 nm. We are supposed to estimate this wavelength theoretically using this equation (energy change in a 1D box), where $N$ is the number of ...