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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2
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0answers
241 views

Graph theory, isomer enumeration and chemical graph theory

Where could we find a good description of graph theory applied to the general problem of isomer enumeration and chemical graph theory?
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13k views

Thermodynamics adding salt to water changes the temperature

$5\:\mathrm{g}$ of an unknown salt are dissolved in $325\:\mathrm{g}$ of water. Both the water and the salt are initially the same temperature. The water's temperature falls by $11.4\:\mathrm{^\circ{}...
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Which way does this reaction between NaCl and acetic acid naturally proceed?

Here is the overall formula: $$\ce{CH3COONa + HCl <=> NaCl + CH3COOH}$$ (sodium acetate + hydrochloric acid $\ce{<=>}$sodium chloride + acetic acid) Which way does the above reaction ...
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Making a reasonable slab of alpha quartz

I want to perform a molecular dynamics simulation with alpha-quartz as my mineral surface. I want to study adsorption of water on alpha-quartz. The most dominant error that I came up with is the ...
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4answers
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Does a first order reaction really get completed only at infinity?

For a $1^{\text{st}}$ order reaction $ A \rightarrow B$, the corresponding rate law is: $$\text{rate} = k[A]^{1}$$ and the integrated rate law for this is $$ \ln \left(\frac{A}{A-x}\right) = kt$$ ...
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Why doesn't a table sublimate, while ice does?

A table does not sublimate, and nor does a spoon. Ice does, however. What is the fundamental difference?
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1answer
1k views

How to calculate the number of moles present in a litre of saturated solution?

The solubility product of a salt having same molecular formula as $\ce{Ca_3(PO_4)_2}$ is $1.08\cdot10^{-28}$. Then find the number of moles of ions present in the saturated solution. My approach: I ...
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Relationship between magnitudes of forward and reverse kinetic rate constants

Consider the reversible unimolecular reaction: $$\ce{A <=>[k_1][k_2] B}$$ We know that the forward reaction is often considerably more thermodynamically favourable than the reverse reaction, ...
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1answer
5k views

What attributes cause a substance to be nonconductive or conductive

I understand what causes elements to be conductive or nonconductive. But what causes a substance say rubber to be nonconductive at a molecular level?
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7k views

Semi-Infinite Potential Square Well: Negative Potential

I am having trouble with a problem involving a Semi-infinite potential square well: I have written down some notes that I added to the post. I have problems understanding the physical situation. See ...
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1answer
1k views

pH of a solution of acetic acid and ammonium acetate

After studying ionic equilibrium, I was just making some wild questions and I was unable to calculate the $\ce{pH}$ of this solution. Assume, 1 mole of each was added to $1L$ solution of water. My ...
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1answer
96 views

How to determine the volume of a substance produced when only given the equation at STP?

At standard temperature and pressure, what volume in $\pu{mL}$ of $\ce{H2O}$ is produced in the following reaction? $$\ce{2 KOH(l) + H3PO4(l) -> K2HPO4(l) + 2 H2O(l)}$$ Most questions I've ...
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What is the minimum pressure for existence of a liquid solution?

The minimum pressure for the existence of liquid solution is $0.6\;\mathrm{atm}$ $0.8\;\mathrm{atm}$ $0.77\;\mathrm{atm}$ $0.9\;\mathrm{atm}$ Although this seems to be an informative question, I ...
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1answer
1k views

How to calculate the Gibbs free energy from the equilibrium constant for the decomposition of sodium bicarbonate?

Solid $\ce{NaHCO3}$ is heated to $90~^\circ\mathrm{C}$. At equilibrium the total pressure of the gases produced is $0.545~\mathrm{atm}$. Calculate $\Delta G^\circ$ at $90~^\circ\mathrm{C}$ for the ...
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Calculate the standard oxidation potential from given potentials

The standard electrode potentials for the following redox couples are given as: >$E_0(\ce{Fe^{2+}/Fe}) = x~\mathrm{V}$ and $ E_0(\ce{Fe^{3+}/Fe^{2+}}) = y~\mathrm{V}$ What will be potential $E_0(\ce{...
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853 views

Comparing formula for enthalpy change with bond dissociation energy and formation enthalpy

I learnt that given a reaction: $$\ce{A -> B}$$ the enthalpy change is given by: $$\Delta H = \left( \begin{array}{c} \text{total enthalpy of}\\ \text{bonds broken}\end{array}\right)-\left( \begin{...
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1answer
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Delta G at Equlibrium

Been trying to understand this question. Here is my reasoning: 1) True, because T is positive (105 + 273)K while ΔS should obviously be negative because the final entropy is lower than the initial ...
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2k views

How to calculate the rotational constants for different states from a stick spectrum?

Given a stick spectrum for an unknown diatomic molecule, how do you determine the rotational constants $B_\nu$ for both the excited and ground states given that $$E_{j}=B_{\nu}j(j+1)$$ \begin{array}{...
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1answer
117 views

Probability of measuring a particle in the ground state: having trouble with the integration

I am working on a problem in the context of an infinite symmetric potential barrier around the origin, with barriers at $x=- \frac{a}{2}$ and $x=\frac{a}{2}$. The wave function is a symmetric triangle-...
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1answer
602 views

Solubility and heat release of ytterbium (III) sulfate in water

Question: The plot of solubility of some salts against temperature is given on the right. A salt like $\ce{NaCl}$ can be recovered fully, when dissolved in a solvent and the solvent is removed by ...
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1answer
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What is Inversion Temperature in terms of Joule Thomson Effect? Does Critical Temperature depend upon Inversion Temperature?

I couldn't find a clear answer in my book and on the internet. Please help! Your quick response will be appreciated.
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Normalization of the wavefunction φ(x) = A

I was trying to normalize the wave function $$ \psi (x) = \begin{cases} 0 & x<-b \\ A & -b \leq x \leq 3b \\ 0 & x>3b \end{cases} $$ This is done simply by evaluating $$ \int\...
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1answer
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Calculating Commutator of Differential Angular Momentum

I have tried for hours to calculate the commutator of angular momentum in the differential form, but I cannot get the correct answer. This is my first experience with actually checking if two ...
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1answer
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Vibrational Spectrums of HI, HBr, HF, and HCl

Do you all know of any large graphs for the vibrational spectrums of HI, HBr, HF, and HCl? I need graphs that are large enough to see the spacing between the peaks in the spectra of HCl, HBr, and HI. ...
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How can one come to know how a catalyst affects a reaction when the reaction and the catalyst is known [closed]

How can I come to know how a catalyst affects a reaction when the reaction and the catalyst used is known. I searched the internet for an answer but could not find one.
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1answer
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Titration of sulfuric acid with sodium hydroxide

$55.0~\mathrm{mL}$ of $0.250~\mathrm{M}~\ce{NaOH}$ is used to titrate $35.0~\mathrm{ml}$ of $\ce{H2SO4}$. What is the molarity of $\ce{H2SO4}$? I know that the equation for this reaction is: $$\ce{...
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3answers
837 views

Understanding Beta Decay

Reading Wikipedia on "Beta Decay" they list the equation of Carbon-14 decaying into N-14. see equation https://en.wikipedia.org/wiki/Beta_decay I presume the 14 refers to total protons and neutrons. ...
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1answer
50 views

Stationary state mass balance with bypass [closed]

A product should be treated with an air that holds 25% humidity. It is provided with an air with 95% humidity, so it is necessary an absorber to dehumidified with silica gel. The silica gel reduced to ...
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Why does water volume decrease when salt is added?

Why does water volume decrease when salt is added? Our teacher asks us in the class but I don't find any strong reason.
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Why weren't the electrons attracted to doubly charged Helium particles in the Rutherford experiment?

I have a chapter and in it there was a topic on the Rutherford experiment. It is written that doubly charged helium particles or alpha particles were thrown towards a very thin gold foil and some of ...
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1answer
2k views

Why is the groundstate electronic degeneracy of monoatomic O(g) 5?

A problem in my Pchem textbook states that the electronic degeneracy of an oxygen atom is 5. My reasoning leads me to believe that the degeneracy is actually 6 (S = 1, L = 1, so (S+1)(L+1) = 6. This ...
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259 views

Addition of salt to ice

Salt is very commonly added to ice even at room temperature to prevent it from melting. Can anyone explain how does it really work?
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1answer
267 views

How strict is the “to excite electrons the energy must equal the energy state difference” fact?

We are always told that to excite an electron from one state to a higher energy states, for example from the valance band to the conduction band, the energy must equal the energy difference between ...
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1answer
607 views

Fraction of concentration of benzene in air water

We have a 120 ml water sample with an unknown concentration of benzene. If the bottle size is 160 ml (with 40 ml of air) and benzene has reached equilibrium, what fraction of benzene is left in the ...
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2answers
1k views

Calculus and physical chemistry [duplicate]

Is calculus and differential equations really that useful in physical chemistry? How does knowing that helps me in physical chemistry? And how much of calculus must I know in order to do physical ...
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1answer
297 views

Octahedral Voids

The total number of octahedral void(s) per atom present in a cubic closed pack structure is (a) 1 (b) 2 (c) 3 (d) 4 PS- I answered it (d) 4 but a key on internet says it is (a) 1. Please clarify ...
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What's the relationship between Van der Waals forces and hydrophobic interactions?

A question on a past exam for a course I'm studying for asks: What's the relation between Van der Waals forces and hydrophobic interactions? From what I understand, Van der Waals forces are ...
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2answers
6k views

Reaction involved in Combustion of Nitrocellulose-Nitroglycerine(NCNG) solid propellant?

I'm working on solid propellant based microthrusters and I am using NCNG as the solid propellant. I want to know the reaction taking place and the mass fraction of the products obtained on combustion ...
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1answer
247 views

Mistake in Wikipedia article on fugacity?

The Wikipedia Article on Fugacity contains statement The contribution of nonideality to the chemical potential of a real gas is equal to RT ln $\phi$ Here $\phi$ is fugacity coefficient.I think ...
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How to judge if a reaction is exothermic or endothermic

Mix $\ce{HCl}$ and $\ce{NaOH}$ together (reactants are at the same temperature) in a calorimeter. The temperature increases, and the book says it's an exothermic reaction. I don't get it. The ...
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1answer
64k views

How do I find the final temperature using specific heat?

What is the final temperature of water and iron if a $30~\mathrm{g}$ piece of iron at $144~\mathrm{°C}$ was dropped into a calorimeter with $40~\mathrm{g}$ of water at $20~\mathrm{°C}$? Specific heat ...
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Calculating the partition function based on molar heat capacity

Given the molar heat capacity of a partition function as a function of temperature, how would one determine the partition function? Say the molar heat capacity = $\alpha T^2$
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1answer
438 views

Proving RTln($a_i$) equal to non PV work done by system,where $a_i$ is activity

We know that chemical potential is defined as ${\mu}_i={\mu}_i^{standard}+RT\ln(a_i)$. Here $a_i$ is the activity of $i^\text{th}$ component of solution. In case of gases instead of $a_i$ it is $f_i$ (...
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1answer
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How does the process of protein denaturatation work?

I know it's the proteins that somehow change their properties at some temparature. But what kind of change, in terms of molecule-level structure?
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What are the physico-chemical processes at play in ironing of clothes?

The process of ironing of clothes removes (to a large extend) the wrinkles that where introduced in the clothes while drying. Obviously this has to be some physico-chemical process that is initiated/...
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1answer
995 views

Activity Coefficients from Electrode Potentials

Lets say we want the activity coefficient of $\ce{Cu^{2+}}$ ions in solution. Would we simply setup one half cell of a $\ce{Cu}$ electrode in a known concentration of $\ce{CuSO4}$ and then connect ...
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2answers
51k views

What is the unit of pH?

I'm making some graphs and I have to label the axes. I want to be extra careful and put the units in even though the meaning of $\text{pH}$ is well known. But I have a problem (though a simple one): $\...
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1answer
125 views

Quotable Literature for the Enthalpy of a Proton

A proton obviously has no electronic energy, no vibrational and no rotational degrees of freedom. Therefore I think it is fair to assume, that $$H(\ce{H+})=\frac32\cdot \mathcal{R}\cdot T$$ holds for ...
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3answers
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Eutectic Phase Diagram and Lever Rule

A solution having composition $p$ (left side of graph) is cooled to just above the eutectic temperature (point $s$ is at $0.18$ $x_{\ce{Si}}$ and the corresponding tie line intersects the liquidus ...
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1answer
313 views

How will the pressure of a gas in manometer change if it goes to a place with higher pressure?

Imagine a manometer where air pressure is $\pu{0.8 atm}$ and the gas pressure is more. We move it to sea level which the air pressure is $\pu{1 atm}$. How will the gas pressure change? (the ...