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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How does Aloe Vera leave a cool feeling on your skin? Why does it evaporate fast?
If you have ever grown Aloe Vera and applied it to your skin, it feels a bit slimy. However, after it evaporates it has a cool feeling on your skin.
Also, why does the Aloe Vera evaporate so fast? ...
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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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A gaseous mixture contains hydrogen atoms in the 4th excited state and helium ion; spectral lines emitted when all these return to the ground state
A gaseous mixture contains hydrogen atoms in the 4th excited state, $\ce{He^+}$ ions in 3d excited state, and $\ce{Li^{2+}}$ in 2nd excited state. Find the number of distinct spectral lines emitted ...
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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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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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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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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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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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Why does CO2 diffuse through a butyl rubber membrane more readily than air?
I am a cyclist, and not a chemist. When I or my cycling buddies get a flat tire out on the road, after removing the offending sharp object (if any) remaining in the tire, we will typically replace 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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Can a spontaneous reaction have zero or negative activation energy?
Is it possible for a certain spontaneous reaction to have zero or negative activation energy?
My high school teacher explains that it shouldn't be possible since it breaks the Arrhenius equation, ...
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Can Gibbs free energy determine whether a reaction is endothermic or exothermic?
In the solution of a problem on thermodynamics, it is mentioned that:
$\therefore$ Reaction will be endothermic if $\Delta G^{o}>0$
In my knowledge, the Gibbs free energy is usually used for ...
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Why is silver(I) phosphate so unexpectedly thermally stable?
Silver(I) oxide is completely decomposed in air already at $\pu{300 °C}.$
Formulate the decomposition reaction and the corresponding mass action expression.
$\ce{Ag3PO4}$ can be melted at $\pu{800°C}$ ...
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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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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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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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Why does the heat of formation of organic radicals and positive ions decrease with their size and degree of branching at the radical or ionic site?
I am currently studying the textbook Mass Spectrometry, third edition, by Jürgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following:
The heat of formation ...
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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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Question about measurement of half-cell potential
I am reading about electrochemical cells from the chapter: Electrochemical cells, Batteries and Fuel cells in the book 'Physical Chemistry' by Thomas Engel and Philip Reid, 3rd edition.
I came across ...
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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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Finding the reaction order from a given plot of chemical kinetics
What will be the order of the reaction for a chemical change having $\log t_{1/2}$ VS $\log a$ Where $a=$ Initial concentration of reactant and $t_{1/2} =$ Half Life?
0 order
1st order
2nd order
None ...
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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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Is a hydrogen molecule smaller than hydrogen atom?
Recently I came across a textbook of physical chemistry which stated the following:
In the formation of a stable hydrogen molecule, two hydrogen atoms share a pair of electrons between them and two ...
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Why delta G = -nFE and not -F * integral(dn*E)?
$\Delta G$ equals the maximum work that a system can do and in redox reactions it's the work done by electrons. According to physics, $W=E\cdot q$; but that's true only if $E$ is constant, however ...
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Why reverse reaction is not possible in the case of dissociation of strong electrolytes and thus non existence of ionic equilibrium?
In chemistry textbooks there is generally written that ionic equilibrium can’t be achieved in the case of strong electrolytes (because their degree of dissociation is almost equal to 1) but it can be ...
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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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Find volume of methanol produced via reaction between carbon monoxide and hydrogen gases
Methanol is manufactured by the reaction of carbon monoxide gas with hydrogen gas. If a $95~\%$ yield is usually obtained, approximately how many liters of hydrogen gas at $\pu{350 °C}$ and $\pu{300 ...
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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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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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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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As electron energy increases, does ionisation energy decrease?
"Electrons are negatively charged, therefore, two electrons repel each other. When electrons are paired in a 3p orbital there is electron pair repulsion which causes the energy of the electrons ...
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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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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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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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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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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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Why don't P graphs contradict Raoult's law graphs?
Our teacher gave us the following question:
1 mole each of liquids A, B are mixed in a piston-type vessel and piston is moved slowly and isothermally. (PA0 = 75 torr and PB0 = 25 Torr)
Find:
(a) ...
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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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What does a fractional order of reaction mean for the mechanism?
I'm doing a high school/sixth form college investigation of the kinetics between magnesium ribbon and hydrochloric acid. I have obtained a rate order was $1.5$ with reference to $[\ce{H+}]$ and hence ...
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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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Why do some elements with high electronegativity exhibit metallic properties?
Metals typically have low electronegativity, which makes them form ions easily and prefer making metallic bonds to covalent. However, some of them seem to disprove that. Take, for example, gold, lead ...
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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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Why is change in gibbs energy not zero through the gibbs free energy equation?
Change in enthalpy of the system is equal to its temperature multiplied by its change in entropy (as change in enthalpy is equal to heat absorbed /given out at constant pressure and change in entropy ...
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