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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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Why does the rate of condensation not continue to increase in a closed system? [closed]

I am trying to understand why the rate of condensation does not keep increasing in a closed system. Initially, as a liquid evaporates, the vapor phase forms, and the rate of condensation increases ...
Peter swift's user avatar
4 votes
1 answer
63 views

Why do azeotropes behave the way they do?

I read this answer to a similar question whilst it proved to be plenty insightful there was this one point I failed to understand: To get a minimum boiling azeotrope, the deviation from Raoult's Law ...
Venven's user avatar
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Does the relation between ΔG° and K vary based on how they are changed?

From the equation ΔG° = ΔH° - TΔS°, I have always been taught that with +ΔH° and +ΔS°, the reaction would be favorable in cases with high temperatures and with +ΔH° and -ΔS°, the reaction would be ...
ptatoe's user avatar
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1 answer
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Why should the pH change when I add sodium hydroxide to water? [closed]

I am a student and I am trying to understand the concept of pH. If I add pure $\ce{NaOH}$ in water, it leads to the formation of $\ce{OH-}$ ions in the water. But this shouldn't lead to any change in ...
Bhaskar Ghildiyal's user avatar
5 votes
1 answer
54 views

What is the particle speed in liquids at an average room temperature (20-25 degrees celcius)?

I've been searching online for ages and I can't find anything related to this, everything seems to be about gas particles relating to temperature. I'm investigating simple chemistry related to ...
Abigail Mckinnon's user avatar
0 votes
1 answer
80 views

Does a decomposition redox reaction with a single reactant and non-elemental products exist?

Does a decomposition redox reaction exist with a single reactant and non-elemental products and that this decomposition reaction cannot be decomposed in any condition to yield elemental products. For ...
user147259's user avatar
7 votes
1 answer
154 views

Overlap of wave functions in Franck-Condon principle

I was revisiting the Franck-Condon-principle and was wondering about one thing. In the Franck-Condon principle, it is stated that if an electronic transition happens, the vibrational wave functions ...
Mäßige's user avatar
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5 votes
1 answer
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Relation between dilution and osmotic pressure

The following question is taken from IAT 2024, an entrance test for research institutes in India at the high school level: Which one of the following plots correctly describes the variation of ...
Aadhaar Murty's user avatar
2 votes
0 answers
72 views

Does copper(II) hydroxide dissolve in ammonia solution?

According to University of Oregon — Chemistry Interactive Demonstrations and Educational Resources — Copper-Ammonia Complex, the equilibrium constant for the formation of copper(II) hydroxide is ...
Shira's user avatar
  • 600
2 votes
1 answer
64 views

Entropy and Internal Energy in irreversible adiabatic process

I have a question related to title. Please see the following discussion: In an irreversible process: $ΔU_\mathrm{irr} = q_\mathrm{irr} + w_\mathrm{irr}$ $ΔU_\mathrm{rev} = q_\mathrm{rev} + w_\mathrm{...
user146901's user avatar
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1 answer
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Do Electron-Withdrawing-Groups give an hypsochromic shift or a bathochromic one? and why?

I'm not familiar with this topic,but i know that bathochromic shifts occur when the energy gap between energy levels of the substituted molecule, are lower than the unsubstituted one;viceversa ...
BugsBunny's user avatar
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Absurd result for the selection rules in the three-dimensional PIB

By using time-dependent perturbation theory and some simplifying assumptions, we know that a transition for a charged particle $q$ from a quantum-mechanical state $m$ to $n$ is allowed if and only if \...
Metal Storm's user avatar
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Mercury meniscus in plastic

Let's suppose you sample mercury in a polystyrene plastic test tube at 25 °C. Would it be expected that the meniscus of Hg is convex (upward curvature) ? I assume that the only possible adhesion ...
Tom's user avatar
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2 votes
1 answer
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How to compute probability of isotope combinations?

I was solving these two questions: Natural abundances of $\ce{^{12}C}$ and $\ce{^{13}C}$ isotopes of carbon are 99% and 1%, respectively. Assuming they only contributes to the mol. wt. of $\ce{C2F4}$...
entropy's user avatar
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Osmotic pressure in a communicating vessel

Let's consider a hollow U tube, at the base of it is a semi-penetrable membrane separating the two sides. On each side is poured in 100ml of, for example, NaCl with different concentration (aM and bM) ...
refined_claymore's user avatar
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0 answers
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Metronidazole physicochemical characteristics [duplicate]

In literature it is not clear whether the drug metronidazole is acidic or basic. However the British pharmacopoeia indicates that an aqueous saturated solution of metronidazole has a pH of 5.8. This ...
Lindo Xulu's user avatar
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If a pocket of nitrogen gas is pumped in at the bottom intake of a padded tank will the pocket of gas bubble up?

I have a nitrogen gas padded tank (tank 1) which is filled from the bottom of the tank. Tank has a set point of 30 psi which adjusted as tank level changes. Also at the inlet is an additional pipe ...
Victor's user avatar
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0 answers
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Law of Multiple proportions

When we define this law we state that the ratio of the masses of the second element in a particular compound is in "small" whole numbers, when keeping the mass of the other constant. How ...
random_curious's user avatar
1 vote
1 answer
62 views

Theoretical justification for the definition of standard enthalpy of reaction

I've been reading the book Chemistry: Core Concepts by Allan Blackman, Daniel Southam, Gwendolyn Lawrie, Natalie Williamson, Christopher Thompson and Adam Bridgeman. They give the following definition ...
russell.price's user avatar
-1 votes
1 answer
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Standard enthalpies of reactions involving multiple gases as reactants

I'm confused by the definition of standard enthalpy of reaction. Consider a reaction which has multiple gases as reactants, such as the one below which shows the combustion of methane. $$\ce{CH4 (g) + ...
russell.price's user avatar
0 votes
1 answer
52 views

Average electronegativity difference in ternary compounds

Villars and Hulliger [1, p. 300] define the average electronegativity difference of a ternary compound $\ce{A_xB_yC_z}$ as follows: $$\bar{\Delta\chi} = 2x(\chi_\ce{A} - \chi_\ce{B}) + 2x(\chi_\ce{A} ...
Suhas Adiga's user avatar
-1 votes
1 answer
87 views

Does increasing temperature increase the rate of gaseous reactions?

In chemical kinetics there is a generalised statement that the rate of reaction is dependent upon the concentration of reactants (except for zero order/complex reactions) temperature catalyst surface ...
Adhway's user avatar
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3 votes
2 answers
268 views

Ways in which total volume changes

Are there fundamentally two ways for volume of total solution might not be preserved? Under the assumption that outside factors, such as pressure and temperature, remain invariant… Chemical reaction: ...
Kutasov's user avatar
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Why does book tell me, n-atomic molecule has 3-6 degrees of vibration?

This book ("Lehr- und Arbeitsbuch Physikalische Chemie" by Gerd Wedler) is generally known as being a very rigorous physical chemistry book, so I don't think it's a mistake? Why is a n-...
iwab's user avatar
  • 383
2 votes
2 answers
1k views

Why does entropy increase on mixing two ideal liquids?

Why does entropy increase when we mix two ideal liquids? In my opinion entropy shouldn't change. Say we have two beakers of equal volume filled with $\ce{H2O(l)}$. I mark them red and blue (the ...
Gauransh's user avatar
-2 votes
1 answer
44 views

Why does increased reaction temperature favor endothermic but not exothermic reactions? [closed]

Why does increasing the reaction temperature favor the endothermic but not exothermic reaction? Increasing the reaction temperature will increase the molecular movement no matter reactants for ...
Li Cheuk Hin's user avatar
0 votes
2 answers
141 views

Mathematical proof that more work is done in an isothermal than an adiabatic expansion? [closed]

Work in an isothermal process is expressed as $$W=-\int_{V_0}^{V}\frac{nRT}{V}dV=-nRT\int_{V_0}^{V}\frac{dV}{V}=nRT\ln\left(\frac{V_0}{V}\right)$$ while work in an adiabatic process is expressed as $$...
NH261108's user avatar
2 votes
1 answer
43 views

Isobaric expansion vs Isobaric Free Expansion [closed]

Our teacher while teaching thermodynamics talked about free expansion, isothermal free expansion and adiabatic free expansion. But for isobaric free expansion, he said that's not possible (it's not a ...
Slater's user avatar
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6 votes
0 answers
115 views

Why is the R-branch in rovibrational spectroscopy bigger than the P branch?

I was conducting a rovibrational IR experiment and noticed that for HCl, the P branch is always lower in intensity than the R branch. I already understand that the intensity of the spectral lines is ...
Mäßige's user avatar
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0 votes
1 answer
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Distance between 2 layers of graphite

We were required to find the distance between two graphene layers of a graphite structure. We were given the atomic radius of carbon as $r_c$ and the bond length was to be considered equal to double ...
JackSparrow's user avatar
0 votes
1 answer
104 views

Closest attempt to making a Carnot Engine [closed]

My professor, a firm believer in electric cars, and I have engaged in a debate regarding the convenience of internal combustion engine(ICE) based vehicles in today's economy, (especially in my country)...
Ronith's user avatar
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-1 votes
1 answer
85 views

Enthalpy of reaction with equal amounts of gaseous products and reactants

At a constant pressure and temperature the enthalpy change for a reaction (assuming ideal gas law) is given as $$\Delta_\mathrm{rxn}H = \Delta n_\mathrm{g}C_pT,$$ where $\Delta n_\mathrm{g}$ is the ...
Unlogical Chymist's user avatar
4 votes
0 answers
85 views

Maxwell Boltzmann Curve two peaks

In the image, the second peak appears lower and more plateau-like. What is the chemical reasoning behind this phenomenon? While I understand the relationship between temperature and peak height (with ...
user avatar
0 votes
0 answers
26 views

How does a conc. electrolyte solution extract water from a organic phase like diethyl ether or ethyl acetate?

In organic chemistry, often, during the last steps of a workup we use concentrated brine solution (NaCl) to "extract" the water from the organic layer, especially when we have an organic ...
TheBorcanu's user avatar
8 votes
1 answer
1k views

Melting point of sulfur

The melting point (m.p.) of rhombic sulfur is 385.8 K while the m.p. for monoclinic sulfur is 392 K. Also, the transition temperature of rhombic to monoclinic sulfur is 369 K. Now, consider heating ...
KeShAw's user avatar
  • 163
0 votes
1 answer
50 views

Total pressure of saturated solution of air and Benzene [closed]

The question asked for me is - A sample of air is saturated with benzene (vapour pressure =100 mm Hg at 298 K) at 298 K, 750 mm Hg pressure.If it is isothermally compressed to one third of its initial ...
Navanieeth TS's user avatar
0 votes
1 answer
58 views

Effect of temperature on voltage of a galvanic cell can't use Nernst equation? [closed]

Is it worth investigating the effect of temperature on EMF in a galvanic cell? I suspect the change will be very very small and maybe impossible to test precisely in a high school lab. This article ...
Mr. Mister's user avatar
3 votes
0 answers
68 views

Why is a C=C weaker than a C=N and even weaker than a C=O when C-C is stronger than C-N and C-O?

Why is a C=C bond weaker than a C=N and even weaker than C=O ? In terms of orbital overlap it doesn't make sense, since there is a difference in energy between the orbitals which lower the interaction ...
TheBorcanu's user avatar
4 votes
1 answer
99 views

Gibbs energy of an imperfect crystal

Our materials professor likes to do Kahoot quizzes and I am confused about why the following statement is true: A defect in a crystal gives it higher energy. I know that an imperfect crystal has a ...
Christian's user avatar
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0 votes
0 answers
26 views

The subscript on orbitals give equations for nodal planes

I've just learned about orbitals and I have noticed a peculiar pattern. If you take the subscript of the orbital name say in dx²-y² you take x²-y² and set it equal to 0. x²-y² = 0 It ALWAYS gives a ...
Shashank Priyadarsi's user avatar
0 votes
1 answer
130 views

Why is phosphoric acid a weak acid?

What is the reason for the phosphoric acid $\ce{H3PO4}$ being a weak acid despite having a structure similar to that of sulfuric acid $\ce{H2SO4}?$ I found some sources claiming that the resonance of ...
Kampann's user avatar
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1 vote
0 answers
65 views

Are there ionic compounds that dissolve in water but do not dissasociate into their ions?

I would assume such a molecule would be possible because polar ionic compounds have a partial charge that can help them dissolve in water yet not disassociate into their ion parts, but I am not sure.
Kryptic Coconut's user avatar
9 votes
1 answer
859 views

Are London dispersion forces in xenon tetrafluoride strong enough to make it a solid?

Xenon_tetrafluoride ($\ce{XeF4}$) is a well-known square-planar molecule with no dipole moment. Molecules are thus have to be bound to each other by London dispersion forces (LDF) which are known to ...
Mikhail Petrov's user avatar
1 vote
0 answers
36 views

Strain energy, binding affinity, penalties in protein-ligand interactions

I am not sure I understand the concepts of penalties and the relationship between strain energy and binding affinity in protein-ligand interactions. I was reading that strain energy can be calculated ...
WithSci's user avatar
  • 111
8 votes
5 answers
2k views

What happens to the waste products from crude oil refining?

The process of refining of crude oil is used to separate crude into fractions of various derived products. For example, crude contains fractions of gasses such as methane, ethane, propane, butane, ...
user98325692's user avatar
2 votes
0 answers
57 views

Difference in the absorption spectrum of gaseous atoms and complex ions

An absorbance spectrum is a graph that shows how much light is absorbed by the material at each wavelength of light. Both spectra are due to electronic transition, but for gaseous atoms, this spectrum ...
Ronith's user avatar
  • 1,405
2 votes
1 answer
91 views

Why Is HOI a weaker acid than HOCl?

In HOI, the oxygen would be more negatively charged than the oxygen in HOCl because iodine is less electronegative than chlorine. Thus the O-H bond in HOI would be more polarized, which would mean it ...
Kryptic Coconut's user avatar
3 votes
0 answers
55 views

Interpretation of IR spectrum

I was trying to identify the following IR spectrum as part of an exercise sheet of my spectroscopy course. What I know from the spectrum, is that we have broad OH stretching vibrations at $\pu{3200-...
Mäßige's user avatar
  • 265
0 votes
0 answers
22 views

How to extract Copper from softgel?

I have an assignment. I need to determine the concentration of copper in a pharmaceutical product using UV-Vis spectroscopy. The product is Chophyll of Healthy America, a softgel that contains: copper ...
Juan Cobos's user avatar
3 votes
1 answer
111 views

Effect of Pressure on the Position of Equilibrium

The following general reaction proceeds with decrease in amount of substance, so increasing pressure should shift the position of equilibrium to the right. $$\ce{2 A(g) <=> B(g)}$$ But let's say ...
Muhammad Ali's user avatar

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