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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24 views

Calculating the cell voltage given the concentration of hydroxide ions

This is the problem that I'm attempting to solve: Alkaline batteries undergo electrochemical reaction given by the overall reaction shown below: $Zn_{(s)}+2MnO_{2(s)}\rightarrow ZnO_{(s)}+Mn_{2}O_{3(...
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2answers
373 views

Pressure exerted by a particle of ideal gas

There is a step I fail to grasp in the proof that for a monatomic ideal gas, $U=\frac{3}{2}PV$, where $U$ denotes the internal energy of the gas. The proof involves considering a particle with mass $m$...
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1answer
34 views

Existence of Hartree–Fock limit

I'm reading McQuarrie's Physical chemistry textbook [1]. On p. 281, the author explains: If we use a more flexible trial function of the form in which $\psi(\mathbf{r_1},\mathbf{r_2})$ is a product ...
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1answer
2k views

Finding root-mean-square speed of neon using kinetic energy

Find the root-mean-square speed of $\ce{Ne}$ atoms at the temperature at which their kinetic energy is $\pu{6.24 kJ mol-1}.$ I tried using the kinetic energy formula $$\mathrm{KE} = \frac{mv^2}{2},$$ ...
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physical chemistry [closed]

Ethanoic acid and ethanol react reversibly to form ethyl ethanoate and water. (It doesn't matter if you have never come across this before.) In a closed system, a dynamic equilibrium is set up....
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4answers
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What roles do neutrons play in an atom?

An atom typically consists of electrons, protons, and neutrons. Electrons are negatively charged and participate in bonding to stabilize the atom. Conversely, protons are positively charged and ...
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27 views

HSAB theory details

I have read a bit about HSAB theory and its applications, but I couldn't find sources for details about the theory and especially the direct explanation for the reason of that phenomena.So, what books ...
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0answers
26 views

Primary kinetic isotope effect

Why does the transition state in both protonated and deuterated molecules have the same energy? My textbook assumes that during transitional state the isotopic bond is half-broken or on its way to ...
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Mulliken Spin Density

I would like to know if a Mulliken population analysis to calculate spin densities is in general a valid choice. I see that it is made use of, for example here1. So up to-date researches apparently ...
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Enthalpy of Atomisation [closed]

Is there any difference between the enthalpy of atomisation of H2 molecule and enthalpy of atomisation of H..Why or Why not ?? Because The Wikipedia definition says that for a molecule it is defined ...
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Correct representation of Lewis structure for sulphate ion

sulphate ion has tetrahedral geometry as predicted by VSEPR theory; the four S-O bonds are indistinguishable and have the same bond order, so the Lewis structure is better represented avoiding S=O ...
4
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1answer
132 views

Why is platinum denser than gold?

The atomic masses of gold and platinum are 196.96657 u and 195.084 u respectively, meaning that (on average) an individual gold atom is heavier than an individual platinum atom. At the same time, the ...
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4answers
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How does iceskating work?

I was willing to understand a little bit better the physics behind iceskating. Messy thoughts From New Scientist (1964) (probably not the most up-to-date reference $\ddot \smile$), I found a diagram ...
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26 views

When, if ever, can standard enthalphy be subsituted for standard chemical potiential?

I'm reading through a combustion modeling paper by Gordon & McBride which is a bit scant on some of the algebra & calculus used to derive their equations. My advisor and I have derived nearly ...
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3answers
8k views

Why isn't the American nickel magnetic?

I never thought that modern American nickels actually contained nickel anymore. However, according to this wiki article, the coins actually do contain 25% nickel, the rest being copper. And yet, no US ...
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Electroplating of Copper

I know that oxygen gets liberated at the anode in the electrolysis of aqCuSO₄ solution in the presence of inert platinum electrodes as the oxidation potential of H₂O is higher than that of SO₄²⁻,...
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1answer
74 views

Apparent paradox regarding spontaneity

Consider the following analysis ( rev and irrev respectively refer to a reversible and an irreversible path, between the same initial and final states): $dU_{rev}=dq_{rev}+dw_{rev}$,and,$dU_{irrev}=...
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2answers
206 views

Decay scheme of sodium-24

Sodium-24 decays into an excited nucleus of magnesium-24. Magnesium reaches nuclear ground level via two consecutive gamma emissions. What are the half-lives (time scales) for these two processes? I ...
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1answer
77 views

Colour due to transmission and reflection

It makes sense to me that when looking through a sample (observer | sample | light), it should appear as the opposite of the light absorbed, but it does not make sense to me to expect the same when ...
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Doubt of solid state [closed]

A compound is formed by two elements Y and Z. Y ions in 2/3 of octahedral holes and 1/3 octahedral holes are vacant in closest packed array of Z ions. The formula of the compound is. (Options: Y2Z3, ...
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7answers
516k 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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2answers
63 views

Reversibiliy and equilibrium

My textbook states "A system is in thermodynamic equilibrium if it is in Thermal, Mechanical, and chemical equilibrium simultaneously". The Wikipedia article on "reversible processes&...
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2answers
5k views

Stoichiometric defects in silver bromide

Stoichiometric defects (Schottky and Frenkel defects) in ionic crystals are formed due to irregularities in the ionic arrangement which maintain the stoichiometry and electroneutrality of the solid. ...
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1answer
569 views

Salt Hydrolysis

Referring to this, when "hydrolysis of a salt" is its reaction with water: How is it that both the cation and anion of the salt are reacting in an equal amount with water? To state this specifically ...
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1answer
665 views

Can silicon dioxide melt at 20 °C?

Can $\ce{SiO2}$ melt at $\pu{20 ^\circ C}$? I have searched the web for $\ce{SiO2}$ phase diagram, but it seems to me that almost all the graph I can find have the temperature axis where the minimum ...
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1answer
54 views

Henderson-Hasselbalch Equation when pKw is not standard [closed]

The henderson-hasselbalch equation is $\mathrm{pH} = \mathrm{p}K_\text{a} +\log\frac{[\ce{A-}]}{[\ce{HA}]}$. How does it change when $\mathrm{p}K_\text{w}$ is not standard?
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1answer
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Calculating dissociation constant at different pKw values

What are the standard approaches to calculating how dissociation constants for acids and bases, $\mathrm{p}K_\mathrm{a}$ and $\mathrm{p}K_\mathrm{b}$, change as the ionic product of water, $\mathrm{p}...
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1answer
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Vapour Pressure of solutions and mol fractions

From a solution (ideal) which contains the components A and B ,the vapours over the solution at a temperature T are collected and condensed into liquid and again brought to the same temperature T. ...
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1answer
41 views

I am having trouble with this question on net ionic equation [closed]

Convert into molecular equation: The reaction between potassium dichromate, ferrous sulphate and sulphuric acid:- Cr2O7^2- + 14H^+ + 6Fe^2+ ---> 6Fe^3+ + 2 Cr^3+...
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1answer
68 views

Is reverse osmosis a fancy term for filtration?

In Reverse Osmosis (RO) systems, the water to be purified is pushed against a semipermeable membrane and comes cleaner the other side, the path of water is the reverse of regular osmosis, hence the ...
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3answers
1k views

How does electrolytic conduction depends on the size of ions & their solvation?

The textbook says, The smaller the effective size of the ion after solvation, the greater will be its conducting power." But, on the Internet, it is explained as follows: Radius decreases, ...
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Effect of temperature on rate constant and Arrehenius [closed]

Please solve the attached question of Chemical kinetics with proper explanation. Thank you
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2answers
49 views

Positive work in the Carnot cycle

In the Carnot cycle the overall work done on the piston is positive. I am having trouble with the real meaning of that. Does positive work mean the piston is moved up and has, over the course of the ...
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1answer
60 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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1answer
38 views

Multiday lab courses in classic chemistry [closed]

This time of the year I usually get some extra income I can use on interesting courses. Usually rescue or sport courses. However, I also have a master degree in chemistry, and would like to spend some ...
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1answer
59 views

What is the number of electrons being transferred in electrolysis of aluminum oxide? [closed]

$$\ce{ 2/3 Al2O3 -> 4/3 Al +O2}$$ As we know, to find the Gibbs free energy, we need to use this formula: $$ G= -nFE^\circ$$ What would $n$ be in this case? After breaking it down into the half ...
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1answer
36 views

Benzene - MO states [closed]

When constructing the different combined molecular orbital combinations (from the original 6pi orbitals) we normally say that p orbitals "combine" to produce the different molecular orbitals ...
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2answers
57 views

What is the differnce between energy and enthalpy?

I cannot understand the difference between thwe two although the internet suggests me there is a difference. Even asked my chemistry teacher but he could not give an explanation.
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2answers
13k views

Why is CO practically nonpolar?

This question was in my book. According to me CO should be polar as it should have a dipole moment. But I found that the $\sigma$-electron drift from C to O is almost nullified by the $\pi$-electron ...
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2answers
900 views

Why is the rate of a reaction always positive and why? [closed]

Why rate of reaction can never be negative? And why rate is an experimental derived expression?
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1answer
102 views

Why does de Broglie wavelength lambda = c / frequency?

For a chemistry problem, I want the velocity of the de Broglie wave to agree with one of these values: A) $c^2/v$ B) $h\nu/mc$ C) $mc^2/h$ D) $v\lambda$ We know that $$\lambda = \frac{h} {mv}$$ But ...
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I have a doubt regarding redox reactions [duplicate]

Oxidation state of P in PH3 is? On drawing structure, it's very evident that P has single bonds with H and had one lone pair. Now as Electronegativity of P>H, shouldn't Hydrogen have -1 charge and ...
0
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1answer
49 views

Expression of the potential in the hydrogen atom while solving radial part of the wave function

I was reading about the derivation of wavefunction of Hydrogen atom from Atkins book. After the separation of variables and writing the wave function, $\psi_{(r,\theta,\phi)}=R_{(r)}Y_{(\theta,\phi)}$...
2
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1answer
51 views

Phase equilibrium in mixtures [duplicate]

How should I determine the total number of phases that are at equilibrium with each other in a multi-component mixture? For example, this problem is from the 2007 GRE published by ETS (Problem 24): ...
5
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1answer
47 views

Vibrational state dependency of the reaction cross section

I'm reading p.1238 of Mcquarrie's Physical Chemistry: A Molecular Approach textbook. In the last line of the page, the author explains that the value of the reaction cross section in the constant ...
2
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2answers
3k views

Does 11.2 dm3 of nitrogen consist of 0.5 moles at STP?

Which of the following statements is true? $\pu{11.2 dm^3}$ of nitrogen at STP- A: has a mass of $\pu{14 g}$. B: consists of $\pu{0.5 mol}$ atoms. My instinct was that the answer is B because any gas ...
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2answers
32 views

If acid releases proton then how can a proton react with another proton to form hydrogen gas? [duplicate]

As we know that acid releases proton (H+ ion) when dipped in water hydrogen has a proton and electron only . To form H+ hydrogen releases 1 electron and it becomes proton. But when Acid reacts with ...
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2answers
49 views

Do commuting operators always share the same eigenfunctions?

Do commuting operators always share the same eigenfunctions? Could you kindly explain to me if this is true or false and examples for this, as I am a little confused.
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1answer
39 views

Does standard electrode potential depend upon temperature?

Does standard reduction potential depend on temperature? I am confused because my institute gives the definition for standard reduction potential as the potential that is measured at standard state ...
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2answers
15k views

Finding the average rate of consumption

The question is: If $2.0 \cdot 10^{-4}$ moles of dye in $\pu{50 mL}$ of solution is consumed in 188 seconds, what is the average rate of consumption of dye in $\pu{mol L-1 s-1}$? I am not sure if I ...

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