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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Pl questions NnO nanoroid [closed]
This is the PL result of ZnO nanorods, but what causes the peak at 650 nm?
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Calculation of formation heat given molar heat capacities and reaction enthalpy
Consider the following reaction for the formation of liquid water at $\pu{298 K}:$
$$\ce{H2(g) + 1/2 O2(g) -> H2O (l)} \quad \Delta_\mathrm rH = \pu{-286 kJ/mol}$$
If molar heat capacities (at ...
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Reaction kinetics exercise for hydrogen iodide synthesis
The rate constant for the reaction of hydrogen with iodine is $\pu{2.45E-4 M-1 s-1}$ at 302 °C and $\pu{0.905 M-1 s-1}$ at 508 °C.
a. calculate the activation energy and Arrhenius preexponential ...
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In self ionization of water, why do we write concentration of water in expression for equilibrium constant?
If we take self ionization of water, then water is a solvent so why do we write concentration of water in equilibrium constant? Can't it be product of concentration of H+ ions and OH- ions? In that ...
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Why does the reaction "pause" when the battery is not connected to a circuit? (or does it?)
The general set up, In an alkaline battery, the negative electrode is zinc (Zn) and the positive electrode is manganese dioxide (MnO2). The alkaline electrolyte of potassium hydroxide (KOH)
At the ...
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volume of oxygen in air question [closed]
I've come across a question and would appreciate any hint on it.
It was problem 3 from the 1st International chemistry olympiad (1968). Here is the question and solution:
For 3.1, I wrote down the ...
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Electrochemical double layer formation
I was revisiting some of my notes about the electrochemical double layer but I have some doubts, and even the textbook of Bard and Faulkner could not really help.
In electrochemical systems, at the ...
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How do you determine the Pull Direction for a GROMACS umbrella sampling simulation to generate the most accurate free energy value? [migrated]
I am trying to calculate the free energy between a protein and aptamer using GROMACS. Literature has indicated that one of the best way to do so is by performing an umbrella sampling MD simulation ...
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Why is the standard enthalpy of formation temperature-dependent in JANAF tables?
I'm unsure why $\Delta_\mathrm{f}H^\circ$ within the NIST-JANAF Thermochemical Tables [1] is temperature-dependent. Wouldn't the $\Delta_\mathrm{f}H^\circ$ represent the enthalpy of formation at the ...
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How to compute solvent reorganization energy in Marcus' non-equilibrium approach?
I try to solve the following equations for some system solvated in the water. The goal is to obtain value in kcal/mol. Unfortunately, I cannot reach the desired output. May someone help me?
The ...
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Small (personal) scale sea salt production?
I was looking to try to make a small setup for producing small amounts of sea salt. Ideally a series of evaporation chambers, with a heavy brine as the finished product, that could then be baked. May ...
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1
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In JJ thomson's cathode ray experiment why is the effect of gravity on the electron not considered? [closed]
Explaining the setup:
The experiment is described in the picture.
Instead of the magnets in the picture imagine two circular coils on both the sides with current running through it, this creates a ...
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SSITKA - In Operando Transmission IR [closed]
Question:
SSITKA: a method to measure the active surface area of a catalyst while it
is under reaction conditions. This is perhaps the most accurate method
to measure the number of sites because the ...
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Determination of ground state energy that has the same L and S values
Determination of the energy of a multielectron atom in the ground state can be estimated using the atomic term symbol which involves the values L, S and J. If an atom has the same L and S values ...
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How to convert molar volume to volume?
This seems like a simple question that people must have asked already, but I can't find an answer online.
I'm not a chemist, but need to use a code that deals with thermodynamics. I am trying to use ...
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Is gas solubility independent of pressure?
My physical chemistry textbook poses this question:
Prove the statement that an alternative way to express Henry’s law of gas solubility is to say that the volume of gas that dissolves in a fixed ...
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How can enthalpy of an ideal gas be independent of pressure?
I know that when one applies a manipulation of the Ideal Gas Law to the Maxwell Relations the result that enthalpy is independent of pressure tumbles out of it, i.e., (dH/dP) = 0.
I don't understand ...
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How to perform NBO calculations at each point while scanning the bond length?
For a given bond, I would like to perform an NBO calculation for each structure while scanning the bond lengths.
Can I use Opt=ModRedundant in combination with pop=nbo? Simply specifying both ...
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3
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Possible error in textbook question? (Heat transfer)
I am dealing with either (a) a severe misunderstanding of the question, or (b) a wrong textbook answer.
Here is question verbatim:
A jacketed vessel is used to heat a water stream using steam
...
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Where does the relation Λm=κV come from? is it experimental?
I was learning about molar conductivity in electrochemistry and this relation
Λm=κV
came up in my textbook. it somehow '...
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First order kinetics
Finding time t in a first order reaction (JEE Adv 2019)
In reference to the above question,taking into account the stoichiometric coefficient, the standard equation of first order reaction time ...
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2
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Fractional Distillation Question
We're covering fractional distillation in my physical chemistry class. I'm confused regarding this diagram:
From your starting point, you heat the binary mixture (in this case benzene and toluene) to ...
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Half life of first order reaction maths
In first order reaction , t 99.9% ( time taken for 99.9% completion of reaction ) comes out as 10 x half life time. So you can either say that a reactant [A] ( A -> product , elementary reaction ) ...
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Doubt regarding isothermal reversible process- Thermodynamics
Since its a reversible process, I can say
$P_{ext}=P_{int}\pm dP$ so now
$W_{int}=\int_{V_1}^{V_2} P_{int}dV$
My question is why can't I assume $P_{ext}=P_{int}$ here and take it as a constant ...
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Mulliken Labels: How do I tell apart E, doubly degenerate, symmetry apart from T, triply degenerate, symmetry for a molecular orbital?
With A and B, it's pretty simple. If you rotate the molecule about its principle axis to where the orbitals line up, and the signs change, it's Mulliken label has a B. otherwise, it's A.
I heard E ...
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How original is my general matrix formula for rate equations?
I was dissatisfied with the method my teacher taught me to solve rate equations, where you're given experimental values for the concentrations of reactants, and the rate of reaction, which given by
$$...
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Why does a Sealed baggie of dry ice lose weight before popping?
Why does a sealed baggie of dry ice lose weight over time at room temp, even before it pops and the gas escapes? I thought it might be due to buoyancy, perhaps? As the bag expands, it displaces air. ...
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What happens to the ions after dissociation in an aqueous solution? [closed]
I'm in high school studying about Buffer Solutions. We had an example of a solution made up of Ammonium Hydroxide and Ammonium Chloride for a Basic Buffer.
NH4OH ⇌ NH4 (+) + OH(-)
NH4Cl ⇌ NH4 (+) + ...
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Is mass of a gas taken into consideration while describing ideal gas law [closed]
According to Avogadro's law equal volume of all gases at constant temperature and pressure contain equal number of molecules.
But how is this possible ??
Imagine helium and radon gas.
In this case is $...
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0
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Need credible source on proof that Van der Waals equation coefficient b if 4 times of the sum of molecular volume [duplicate]
Van der Waals equation coefficient b is approximately 4 times of the sum of the molecular volume. There are different kind of proofs for this. What I am interested in is a very simple one: the centers ...
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How to properly determine number of vibrational modes of CO in carbonyl complexes?
it's been a few years since I took inorganic chemistry and was starting to refresh some of the concepts. What I didn't really understood when I reread was the following: How to properly determine the ...
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Determine potential and electric field distribution between electrodes
I want to analytically determine a simplified potential and electric field distribution around planar electrodes, and an 40nm square electrode in an 50nm insulating well.
I think that the Poisson-...
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Why is the work done on the system not equal in frame of gas and surroundings?
Consider an isothermal irreversible process for an ideal gas in a cylindrical container closed with a piston (system). Initial and final states are $(P_1,V_1,T)$ and $(P_2,V_2,T)$ respectively. ...
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How to obtain the expression for residual Gibbs energy?
The property involved is Gibbs free energy, the equations that I wrote are presented in my text book Introduction to chemical engineering thermodynamics by Smith and Van Ness, Chapter 6.
The thing is ...
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Cyclovoltamogram of silver in solutions of its insoluble salts
Hello I was dealing with the following question in my electrochemistry course:
Sketch cyclic voltammograms for the silver oxidation and reduction in different
electrolytes. Assume electrochemical ...
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Moments of inertia of benzene and ammonia as symmetrial tops
Hello I was reading about symmetrical tops and how their properties relate to their rotational spectra. According to the 8th edition of Atkins, those molecules have one unique principal axis which ...
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How to choose an appropriate electrolyte
I am looking to electroplate using a zinc-nickel coating using an ionic liquid as the electrolyte. How should I go about selecting the proper ionic liquid? I choose the metal coating due to it ...
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Can pure hydronium exist?
Can pure hydronium exist? If not, why not? It seems to me (and I am no chemistry expert) like pure hydronium should have the theoretical maximum acidity or minimum pH that a substance can reach.
Can't,...
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Analyzing Effusion Rates in Gas Mixtures: A Comparative Approach to He and CH4 and problems
Let's start it with a question :
Suppose there is a mixture of $\ce{He}$ and $\ce{CH4}$ Gas in a container of volume $V$ and a certain temperature with a small hole at a wall of the container, the ...
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Semiconductors and their electronic bands [closed]
While studying colors of sulfides and searching for the reason why they are black I came across this question:
https://chemistry.stackexchange.com/questions/138309/the-color-of-the-most-sulfides-of-p-...
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Choosing energy levels for finding quantum numbers
When an element has multiple energy levels (i.e Titanium has $(Ar)3d^24s^2$), what energy level do we use to find the quantum numbers? Is it generally assumed the LAST energy level is used? or is it ...
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Apparent color of nickel(II)chloride and nickel(II)chloride hexahydrate
Why does anhydrous nickel chloride (NiCl2) appear yellow, even though chloride ions are considered weak field ligands, which should result in a smaller ligand field splitting energy and the absorption ...
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Why does burnt milk on bottom of pan have 'vaguely' cork-like pattern?
I burnt milk while boiling it. I noticed that the burnt milk on the bottom of the pan, formed a pattern that vaguely resembled the pattern of cork-cells . Why is this pattern being formed?
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pKa and pKb in solvents other than water
I know that when you have aqueous solutions, then the pKa and the pKb are linked to each other (pKa + pKb = 14). Is there an equivalent relationship between pKa and pKb in non aqueous environments? I'...
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Criterion for Spontaneity for Closed Systems at Constant Volume and Pressure
For a closed system at constant temperature and volume, the criterion for spontaneity is $dA < 0$. However, for a system at constant composition, the total differential of $A$ is given by
$$dA = -...
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2
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What solvents can I use to dissolve Epichlorohydrin rubber and Chloroprene Rubber
I am working with Epichlorohydrin and Chloroprene Rubbers and I would like to cast films of 2 mm at most. The solvents I have in my lab are DMSO, THF, DMF, Acetone, Ethanol and Propylene Carbonate. ...
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Why is octane more volatile than water while having a higher boiling point?
Octane has a boiling point of 120 °C. Water has a boiling point of 100 °C. The definition of boiling point is, "the temperature which the liquid substance's saturated vapor pressure equals the ...
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Temperature change in isobaric processes with and without change in number of molecules
Hello I was thinking about two thermodynamics problems and I wanted to get some insights into how to solve them.
The first problem was: Suppose we have one mole of ideal gas under constant external ...
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How do I express concentration of a substance at the interface between two membranes of different diffusivities and lengths at steady state?
I am lost on this question from my textbook:
"A solute diffuses across two membranes, A and B. The membranes' thickness are $\Delta x_A$ and $\Delta x_B$ respectively. The membranes' ...
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If E° of a Half Cell is based on the chosen reference Electrode (Generally SHE) then how is the equation ΔG°= -nFE° be valid for a Half Cell
For example let us take the reaction:
Zn(s) ---> Zn^2+(aq) + 2e^-(aq) ;ΔG°, which we are considering as our half cell
And now suppose, by taking the value of E° of SHE(Standard Hydrogen Electrode) ...
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