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 can the potential energy at the infinite energy level in an atom be zero?

I have recently learnt about atomic structure and the Bohr model of the atom and have observed a discrepancy between it and my previous knowledge based on physics. For simplicity, assume the atom is ...
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42 views

What will be the form of coulomb and exchange operators for electron m in an n-electron molecule?

I know that the Fock operator for electron $m$ in $n$-electron molecule would be: $$\hat{f}\!(m)u_i(m) = \varepsilon_iu_i(m)$$ $$\hat{f}\!(m) \equiv -\frac 1 2 ∇_m^2 - \sum_α\frac{Z_α}{r_{ma}} + \...
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47 views

Reaction Mechanism with a Rate Determining Step

Just a quick question on how to deal with multiple intermediaries in a proposed reaction mechanism. Here is the overall reaction: $$\ce{I-(aq) + OCl-(aq) -> IO-(aq) + Cl-(aq)}$$ Here is the ...
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23 views

Saturation dissolved oxygen level at pressure

The saturation level of dissolved oxygen in contact with a moist atmosphere is $$c = 0.21(p_\mathrm{atm} - p_\mathrm{vap}) K_\mathrm{H} M$$ where the $p_\mathrm{atm}$ and $p_\mathrm{vap}$ are the ...
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218 views

Degree of Hardness Numerical

To remove the temporary hardness from $5\ \mathrm L$ of $\ce{H2O}$ $5.6\ \mathrm{mg}$ of lime is required. Calculate the degree of hardness due to $\ce{Ca(HCO3)2}$ present in water. My attempt: $$ \...
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48 views

Free induction decay in NMR (as stated in Pavia)

There is a statement in a very popular textbook of spectroscopy by Pavia (Chapter 3, Intro. to Spectroscopy), it says "The observed FID is actually an interference signal between the radiofrequency ...
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24 views

Isobaric-isothermal ensemble with degeneracy

I've been studying statistical mechanics for a while, the topic is very far from what I've learned till now so my questions may be superficial. When trying to see what my entropy is in an isobaric-...
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22 views

Calculating Air Density and Effect of Air Composition

I have to calculate density of atmosphere, assuming that it is: 79% : N2 21% : O2 Does the percentage of gases affect the answer, and how can we find the density with such little information?
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126 views

Enthalpy change of gas expansion against constant external pressure

A certain mass of gas is expanded from $\pu{1 L}$ at $\pu{10 atm}$ to $\pu{4L}$ at $\pu{5 atm}$ against a constant external pressure of $\pu{1 atm}$. If initial temperature of gas is $\pu{300 K}$ and ...
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132 views

How to derive the compressibility factor for a van der Waals gas?

So as far as I know, $$Z=\frac{p_\mathrm{r}V_\mathrm{r}}{nRT},$$ where $\mathrm{r}$ denotes the subscript for real. Solving it for a van der Waals gas gave me the following result, $$Z=1+\frac{p_\...
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28 views

Calculate chemical potentials to find electrode Fermi level

I'm running some simple simulations of the semiconductor-electrolyte interface and I'm having a hard time figuring out the equilibrium condition. Can someone please help me with my electrochemical ...
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19 views

Why do polyoxometalates have good electrochemical/ redox properties?

Many authors are using polyoxomethalates immobilised in carbon nanomaterial as electrocatalysts for energy related reactions (ORR, HER, OER). Other metal alloys have also shown to be successful as ...
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27 views

Freezing point lowering for a mixture of many liquids

I have been taught that if I have a solute of molality $m$ mixed with a liquid, the freezing point in lowered by an amount $K_\mathrm{f}\cdot m$ where $K_\mathrm{f}$ is the molal freezing depression ...
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90 views

How to calculate the cell potential after the reaction has operated long enough for the Fe2+ to have changed by some concentration?

Consider the cell described below at $\pu{261 K}$: $$\ce{Fe | Fe^2+ (\pu{0.925 M}) || Cd^2+ (\pu{0.981 M}) | Cd}$$ Given $E^\circ_\ce{Cd^2+ -> Cd} = \pu{-0.403 V}$, $E^\circ_\ce{Fe^2+ -&...
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68 views

Topic in Salt hydrolysis that I couldn't understand

Salts can be made up of all combination S of ( SA ,WA) and (SB , WB) I understand how to deal with salts of strong acids with both strong and weak bases and also of strong bases with weak and strong ...
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34 views

Can hydrocarbon help to split molecular hydrogen into atoms?

I am a physicist and have the following chemistry problem. When a sample is exposed to H2 (molecular hydrogen), a tiny amount of atomic hydrogen or, maybe, protons is generated. Extremely small ...
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43 views

Rate equation of a radical

Consider the following elementary reaction mechanism where both the forward and reverse reaction mechanism are important $$\ce{CO + O2<->[1] CO2 + O}$$ $$\ce{O + H2O<->[2] OH + OH}$$ ...
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1answer
121 views

Equation for the equilibrium constant for the hydration of carbonyls using UV spectroscopy

I was looking through the literature when I found this source: https://pubs.rsc.org/En/content/articlepdf/1967/tf/tf9676302131 Which states that the equilibrium constant Khyd is: Khyd = $\frac{[...
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45 views

How does mesh size of Barium Chloride affect sulfate results via turbidimetric method?

I am analyzing sulfate using Standard Methods 4500 $\ce{SO4 ^2-}$ E (turbidimetric method) using $\ce{BaCl2}$ and measuring %T at 420 nm. In the past, we used an appropriate 20-30 mesh size for the $\...
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17 views

AFM of Smooth Amorphous Carbon

I have been having trouble getting decent resolution images and clear data of smooth amorphous carbon thin films prepared by RF bias assisted vacuum deposition. I was using a DLC tip in tapping mode ...
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312 views

Calculation of average bond length from force constant and IR absorption?

I need some help beginning a problem set problem (just want hints, I'd like to figure it out myself). The problem gives me the IR absorption for a diatomic, as well as the force constant for the ...
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364 views

What bonding allows chloroaluminate (AlCl4-) to form?

How is $\ce{AlCl4-}$ formed when $\ce{Al}$ only has $3$ electrons in it's outershell. It would be able to give $3$ electrons away with $\ce{AlCl3}$ for it to have a full outershell but how does it ...
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111 views

Rotational barrier of biphenyl in ground and excited electronic states

I'm studying how the energy of biphenyl varies with its dihedral angle. I know how to describe the dependence quantitatively, but still, I don't know how to explain why the rotational barrier of ...
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26 views

Where does hydrogen evolution occur when aluminium amalgam is placed in water - aluminium or mercury?

Let's say a drop mercury is placed on clean aluminium sheet; mercury amalgam is formed. The solubility of aluminium in mercury and vise versa at room temperature is fairly low. If the entire sheet is ...
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170 views

Mismatch in the trends of atomic size and atomic radius

In the periodic table, the atomic radius decreases as we move from left to right in a period. However, the atomic volume should also decrease as a result of the decrease in atomic radius, as volume is ...
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80 views

Absence of anti-Stokes line in Raman spectrum

If we have a molecule 1H-25X which shows a band at $3000~\mathrm{cm}^{-1}$ in the IR spectrum and you want to record a Stokes and anti-Stokes Raman spectrum with a laser of 1000 nm, why is the anti-...
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45 views

How does association within vapor or dissociation within liquid affect the ideal nature of a binary solution?

As I understand, when there is positive deviation of a binary solution from Raoult's Law, the equilibrium partial pressure curve approach ideality (i.e a straight line dependence of equilibrium ...
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57 views

Why do ions form condensation centres in isopropanol vapour?

In cloud chambers the particles are detected when a particle passes through the chamber causing the vapour to condense into a "cloud". What Process causes this observed phenomenon? In other words, how ...
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264 views

Equation to find specific gravity (or density) from a solution of sugar and water

Is there an equation or simple way to calculate the final density of a solution made from x grams of sugar and y liters of water? And would it work in reverse? if we have y liters of water at z ...
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41 views

Stat Mech: Maxwell-Boltzmann Distribution of Momenta

I'm trying to show that the MB distribution of scalar momentum that I've found is properly normalized but I'm stuck. My process: I started with the MB distribution of momentum in 2D and found the ...
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114 views

Barking dog reaction mechanism

Liebig's blue devil or the "barking dog" reaction is the gas phase oxidation of carbon disulfide with either nitrous oxide or nitric oxide. What are the gas phase reaction steps in this reaction, I ...
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31 views

Capillary forces in horizontal plane

In a physical chemistry course, we went to the lab and made a microstamp out of an elastomer. This stamp has gaps of 25 µm in width. When the elastomer had hardened, we placed it on a microscope slide ...
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176 views

Deriving a relation between entropy, volume and particles through the chemical potential

I'm a teaching assistant on a first year course on Introduction to Thermodynamics based on the book "Molecular Driving Forces" by Dill & Bromberg. There's a question which asks the students to ...
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57 views

PTFE-to-PTFE or PTFE-to-Copper pressure seal

I am currently working on an engineering project with a friend. Without giving too much away, I have two parallel strips of Zirconium-Copper alloy sandwiched between an upper and lower piece of smooth ...
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46 views

Is the kinetic gas equation valid for non-cubical containers?

I have seen the derivation of the following equation for a cubical container with $N$ molecules. $$PV = \frac 13 mNu^2 $$ How is this equation valid even for spherical container or any other non ...
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257 views

How is it that I could obtain endothermic Temperature ~ Time plots for a calculated Exothermic Enthalpy of Solution?

I recently conducted a coffee-cup calorimetry experiment in which we attempted to measure if the dissolution of inorganic crystals such as LiCl, NaCl, and SrCl were endothermic or exothermic based on ...
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87 views

What material can be used as scraper in a chemical reactor?

I am having a 10L reactor built using SS316 for Plastic Pyrolysis. TEMPERATURE : 550C I would like a scraper to clean the char that forms on the reactor's inner layer. Teflon scraper is available ...
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26 views

Relationship between Yield and Applied Potentials

This question revolves around this question from Atkins' Chemical Principles 5th ed., Chapter 13, Question 13.116: Consider the electroplating of a metal $+1$ cation from a solution of unknown ...
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75 views

Conductivity variation on Caustic (NaOH) Dilution System

I am reading the drawing for an automatic caustic dilution system where 50% NaOH is diluted down to 20%. I was expecting to see a density sensor on the outlet to provide feedback to the dilution ...
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69 views

Change in Free Energy in Gas Reaction

I try to estimate whether particles form pairs or not. What I know is the difference in the potential Energy $\Delta U_\mathrm{pot}$ which occurs when both particles form a pair. When I have a ...
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31 views

Inverse use of a reverse osmosis membrane

I've got a question regarding Osmosis. I recently came across 'Thin-film composite membranes'. Those are build up of layers with one of those being semipermeable. As I'm not well versed in chemistry, ...
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55 views

ammonia, methylammonia, dimethylammonia, trimethylammonia reactions

Perhaps a "basic" question (pun intended), but I have a few questions about the reactivity of ammonia and its methylated cousins. I come from an engineering background, essentially I use a process in ...
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163 views

Is there any mathematical formula for electron affinity and ionization potential?

I already know about the mathematical formula for electronegativity, but it requires the ionization potential and electron affinity. How can I can easily calculate the ionization potential and ...
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269 views

Do gases behave ideally near the critical temperature?

In class, my TA said the closer the temperature of a gas is to the critical temperature, the more ideal it is. I'm struggling to understand this, as I thought more ideal behavior occurs at high ...
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64 views

Thermochemical data of methanol

I am trying to find the standard entropy and enthalpy of methanol as functions of temperature, but they are not available on the NIST-JANAF tables: http://kinetics.nist.gov/janaf/ Does anyone know ...
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922 views

Critical temperature for an ideal gas

What is the critical temperature for an ideal gas? It can't be found from Andrew's isotherm as it is for real gases and states critical temperature as $\frac{8a}{27 R \cdot b}$, but for ideal gases $a ...
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743 views

What are the effects of frenkel and schottky defects on electrical conductivity of a solid?

How do these two defects impact dielectric constant of solid? Please explain these two questions in detail. In case of frenkel defect the the smaller ions are just dislocated from their initial ...
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94 views

Is it true that un-dissociated HCl exists in dilute hydrochloric acid?

My book says that the equilibrium constant for $\ce{HCl + H_2O}$ is so high that the reaction goes to completion. But that does not make sense since the existence of an equilibrium constant for this ...
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261 views

Does the object blocking the cathode rays in Thomson's cathode Ray experiment need to be opaque?

Thomson kept an "opaque" object in the cathode ray tube and he saw the shadow of the object.then he decide that the cathode rays follow a rectilinear path. But Thomson also discovered that cathode ...
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51 views

What would be a suitable non-combustible lubricating oil or compound for a very high pressure air compression system?

This question came up at Engineering SE but remains unanswered. If we are compressing regular air, not nitrogen, what oil or compound can be used that would not combust with the oxygen in the air. ...