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.
3,499
questions
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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(...
5
votes
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 $m$...
5
votes
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 ...
2
votes
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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votes
0answers
26 views
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....
32
votes
4answers
22k views
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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votes
0answers
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 ...
1
vote
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 ...
4
votes
0answers
44 views
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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votes
0answers
24 views
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 ...
0
votes
0answers
18 views
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
votes
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 ...
7
votes
4answers
1k views
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 ...
0
votes
0answers
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 ...
28
votes
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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votes
0answers
17 views
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⁻,...
1
vote
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}=...
7
votes
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 ...
1
vote
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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votes
0answers
28 views
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, ...
51
votes
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 ...
0
votes
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&...
16
votes
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. ...
2
votes
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 ...
2
votes
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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votes
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
40 views
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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votes
1answer
17 views
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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votes
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+...
2
votes
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 ...
-1
votes
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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votes
0answers
10 views
Effect of temperature on rate constant and Arrehenius [closed]
Please solve the attached question of Chemical kinetics with proper explanation. Thank you
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
1
vote
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 ...
0
votes
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 ...
0
votes
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.
12
votes
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 ...
0
votes
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?
2
votes
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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votes
0answers
14 views
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
votes
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
votes
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
votes
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
votes
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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votes
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 ...
2
votes
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.
0
votes
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 ...
3
votes
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 ...
