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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43 views

Thermal properties of 301 stainless steel

So I know that 301 stainless steel was chosen for the SpaceX Starship rocket as it can handle high temperature differences. What about this alloy makes the steel harden when it gets colder?
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What is the physical significance of the universal gas constant R?

While studying work done in isothermal processes I was told that the universal gas constant $R$ is the work done by the gas per mole per kelvin. I am sure I am missing something basic but I didn't ...
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Comparing van der Waals constant for gases

How can I compare the van der Waals constant $a$ (the liquefication constant) for different compounds based on my knowledge of bonding in the compound? Let's pick the following sample set: $$ \...
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1answer
71 views

Finding the pOH of a buffer from the scratch without the Henderson Hasselbalch equation

I found this question on the internet that said: Find the pOH of the solution obtained by mixing $\pu{0.1 mol}$ of $\mathrm{NH_4 OH}$ $(K_\mathrm b = 10^{-5})$ and $\pu{0.1 mol}$ of $\ce{(NH4)2SO4}$ ...
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42 views

pH for an HA/NaA solution using a contour map

The following question has troubled me for a while now. A virtual weak acid $\ce{HA}$ dissociates as follows: $\ce{HA <=> H^+ + A^-}$ with the acid dissociation constant $K_\mathrm{a} = 10^{-3....
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How does air tight objects stick to walls or any other object? [closed]

How does air tight objects stick,what is the mechanism behind it
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10 g of Carbon is burnt with 22g of O2 to produce both CO and CO2 without any Limiting Reagent. Find mass of CO and CO2 produced [closed]

I read a question as stated above. Is this reaction even possible because as far as I know CO is only produced when there is not enough oxygen. In case it is correct, please provide me with an answer.
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Can we create metals and/or elements artificially, sufficiently enough to replace or eventually replace mining?

Before you answer the question, please note I am not a chemist or a physicist, I'm simply curious. My question is in the context of scarcity. Is it possible to artificially create materials such as ...
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29 views

How to write the Nernst Equation for this reaction?

I am required to write the Nernst equation for the following reaction: $\ce{O_2 + 4H^+ + 4e^- -> 2H_2O}$ Clearly, here $\ce{O_2}$ is getting reduced from an oxidation number of zero to an ...
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1answer
40 views

Relative humidity and vapor-pressure in equilibrium

I have quite an unclear understanding of relative humidity. I am writing my understanding on the topic and please correct me wherever I'm wrong: What I understood: Let's say $\ce{H2O}$ has a (...
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What am I doing wrong in calculating the lattice enthalpy using the Born-Mayer equation? [closed]

I was tasked with calculating the lattice enthalpy of silver iodide using the Born-Mayer equation. To do this, I used the equation given to me: $$H_L = \frac{N_A|Z^+Z^-|e^2}{4\pi \epsilon_\circ d}\...
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1answer
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Why is the aqueous solution of KMnO4 slightly basic?

This is in the context of the various changes in oxidation state the permangananate ion can undergo with the variation of the pH of the medium. Besides the cases of strongly basic and strongly acidic ...
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Physical Chemistry - Chemical Equilibrium [closed]

Q1) N2 (9) + 3H2(9) - 2NH3 (9) Assume K=6, for initial concentration of hydrogen and ammonia at 4 and 0.2 moles, respectively. Calculate for what initial value of nitrogen concentration, the extent of ...
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19 views

What is the fraction by weight of KBr in the original sample? [closed]

A mixture of KBr and NaBr weighing 0.5600g is treated with Ag+(aq) , and all the bromide ion is recovered as 0.9700g pure AgBr . What is the fraction by weight of KBr in the original sample?? First ...
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pH scale is open ended [duplicate]

In most of the textbooks it is stated that pH scale lies between 0 and 14 but I found an article in which it is stated that pH scale is open ended https://pubs.acs.org/doi/pdf/10.1021/ed083p1465.But I ...
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Debye–Waller factors for tin(IV) oxide

How I could find the bulk Debye–Waller factor for tetragonal rutile type $\ce{SnO2}$ at room temperature? I have been doing some online digging with no luck. If anyone has a reference I could use that ...
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2answers
65 views

Determine vmax and enzyme concentration (Michaelis–Menten)

I am given that the enzyme concentration is $\pu{15 nM}$ and the following data: $$ \begin{array}{rl} \hline S/\pu{mM} & V/\pu{mM s^{-1}} \\ \hline 1 & 0.202 \\ 2 & 0.368 \\ 5 & 0....
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Why isn't entropy dimensionless?

The usual units are J/K, however the only reason temperature has different units than energy is because we didn't used to know temperature was just the average kinetic energy of atoms/molecules. ...
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1answer
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Why is the spectroscopic entropy of carbon monooxide higher than that of nitrogen?

While solving a question set, I found a question with this data table (at $\pu{298K}$): $$ \begin{array}{lrrr} \hline \text{Substance} & T_\mathrm b/\pu{K} & S^⦵_\mathrm{cal}/R & S^⦵_\...
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How lyophilic colloids reduce surface tension?

Its given in my textbook that surface tension of lyophilic/hydrophilic solution is lower than water. But my intuition says,since in lyophilic solution the interaction between a lyophilic colloid and ...
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29 views

What is calcined lawsonite?

For context, I am planning to try and use this sample to make a ceramic glaze. I recently collected a sample of what I think is lawsonite, which has the chemical formula $\ce{CaAl_2Si_2O7(OH)_2*H_2O}$....
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How can we explain relationship between two chemical structures using Quantum mechanics(data)?

for example, consider CH3-CH3 (eclipse) and it transformeds to CH3-CH3 (gauche) in molecular dynamics, we can explain structural transformation using Angle, bonds dihegral, and molecular energies. How ...
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28 views

Equilibrium in Gas Phase and Pressure

In one task/example there is gas phase reaction and it is said that reaction takes place at pressure of 1 bar and standard Gibbs energy of reaction is needed to be calculated. In this task 1 bar is ...
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1answer
64 views

Equilibrium constant expression for an acid base reaction

While reading an organic chemistry textbook I saw the following Formula for calculating equilibrium constant of an acid-base reaction Consider following acid base reaction in which $\ce{HA}$(reactant ...
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Radical Chain Reaction, termination steps

In the termination step of radical chain reaction, we often neglect the recombination of hydrogen atom radicals and it will not be included in the mechanism. Let say the reaction is between $\ce{H2}$ ...
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1answer
97 views

Volume of Oxygen Produced By Electrolysis of Water [closed]

I am trying to estimate the volume of oxygen that will be produced by electrolysis of water at normal temperature and pressure with a current of $\pu{50 A}$. The following is my calculation: The ...
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2answers
80 views

Normalization of a free particle in 1 dimension

I am having difficulty normalizing the wavefunction for a free particle in 1 dimension. I have sent an attachment of my working out. My attempt at the normalisation Free electron: $$-\frac{\hbar^2}{2m}...
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Calculation of dispersion energies for organometallic complexes with Gaussian [migrated]

I've tried to calculate dispersion energies of some organometallic complexes with the Gaussian software using WB97XD/Gen (...
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Are the newer measurements for STP commonly used in high school and university textbooks? If not, why?

I read a Wikipedia article that has the following quote: In chemistry, IUPAC changed the definition of standard temperature and pressure (STP) in 1982:[1][2] Until 1982, STP was defined as a ...
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Why does According to Le-Chateliers principle, adding heat to solid and liquid in equilibrium will cause the amount of solid to decrease

According to Le Chatelier's Principle the external changes must be counteracted but in this scenario the external factors causes the amount of solid to decrease because of obviously melting but if Le ...
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1answer
59 views

Effect of impurities on melting and boiling points

I am tutoring my nephew for his science GCSEs; and his chemistry textbook states that you can tell how pure any compound is by how close its melting and boiling points are to the "official" ...
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Hund's rule for comparing term symbol energies in excited state

This question was asked in an exam: The lowest energy electronic state for excited state carbon atom is, a. $^1D_2$ b. $^3D_1$ c. $^3D_3$ d. $^3D_2$ Although we have been taught Hund's rule for ...
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1answer
73 views

Finding mass percent through molality of potassium nitrate solution

Question An aqueous $\ce{KNO3}$ solution has a molality of $\pu{4.16 m}$ and a density of $\pu{1.08 g/mL}$. Calculate the percentage by mass $\ce{KNO3}$ of the solution. My Approach I know that ...
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2answers
70 views

How is kinetic energy accounted for when describing diatomic bonds with a Morse potential?

The Morse potential can be used to describe the potential energy of the a diatomic bond: This curve suggests that the lowest state $v = 0$ is the most stable, since it has the lowest potential energy....
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Practical meaning of omega potential

In statistical thermodynamics, the quantity omega potential is defined and is different for fermions, photons, phonons and other particles. I have been understanding the derivations of omega potential ...
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1answer
177 views

pH of an aqueous solution with acetic acid and sodium acetate

An aqueous solution of $\pu{1L}$ contains $\pu{0.2 mol}$ of acetic acid and $\pu{0.2 mol}$ of sodium acetate ($K_\mathrm{a} = 1.8 \times 10^{-5}$). Compute the $\mathrm{pH}$ . I'm trying to help my ...
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0answers
21 views

Calculating the ionic strength of a histidine solution

I'm trying to repeat the calculation of the ionic strength of a solution containing histidine as a buffer I recently read in a paper. In their paper, the authors calculate the ionic strength of a 20 ...
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0answers
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What does the horizontal axis on cyclic voltammograms mean?

In cyclic voltammograms (like the one in the attached image) what exactly is the horizontal axis' voltage refering to? Is it the measured voltage between the reference electrode and working electrode? ...
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1answer
197 views

Should rates and rate constants be expressed in terms of pressure or concentration?

If an elementary reaction was conducted in the gaseous phase, say $$\ce{X (g) -> Y(g)},$$ would the formal definition of the rate law be $\mathrm{rate} = kP_\ce{X}$ or $\mathrm{rate} = k[\ce{X}]$?
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What is the average distance of two different types of molecules of different concentrations in solution?

Concerning the simplest approximation for intermolecular distance in solution: $d=(\frac{10^{24}}{cN_A})^{1/3}=1.18c^{−1/3}$ This applies for one type of molecule in solution. But, how to account for ...
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Generate fit of virial expansion to osmotic pressure data and obtain second virial coefficient

So I have some osmotic pressure data that I would like to obtain the second virial coefficient ($B_{22}$) for, but I am getting increasingly more confused on how the theory works. I know you can ...
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34 views

Calculate quantity of ions eliminated by acids

I have limescale $(\ce{CaCO3})$ and a solution of hydrochloric acid at 30% concentration of hydrogen chloride $(\ce{HCl}).$ This acid-base equation $$\ce{HCl + H2O -> H3O^+ + Cl^-}$$ with the ...
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1answer
86 views

Relation between enthalpy and internal energy for chemical reaction at constant volume

Question The combustion of benzene(l) gives $\ce{CO2(g)}$ and $\ce{H2O(l)}.$ Given that the heat of combustion of benzene at constant volume is $\pu{-3263.9 kJ mol-1}$ at $\pu{25 ^\circ C}$; heat of ...
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1answer
41 views

Finding the mole fraction of nitrogen in a mixture of nitrogen and oxygen

Question The density of a mixture of Nitrogen and Oxygen is $\pu{4.7 g L-1}$. Its given that $P = \pu{4 atm}$, and that $T = \pu{298 K}$. Assuming both gasses are ideal gasses, what is the molar ...
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1answer
55 views

Finding freezing point depression knowing molality and density

The density of a $\pu{7.71 M}$ $\ce{LiCl}$ solution is $\pu{1.1678 g cm-3}$. Calculate the freezing point depression of the solution. I understand that in order to calculate the freezing point ...
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38 views

Meaning of the thermal energy

Why do hydrogen bonds form and break so readily in water when their energy of 8$kT$ is so much higher than $kT$? Similarly, how can there be dispersion forces (<$kT$) that are not totally overcome ...
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why is unsaturated vapor pressure of vapor present in certain volume of air is equal to saturated vapor pressure of that vapor at dew point?

According to my textbook,unsaturated vapor obeys combined gas law.So if temperature is decreased to dew point temerature,the partial vapor pressure should decrease.If so,why it is stated that the ...
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0answers
32 views

Lindemann-HInshelwood mechanism difference between high and low concentration

I have a gas reaction which follows the Lindemann-Hinshelwood mechanism and want to calculate the rate constant at low and at high concentrations of the gas but I find myself stuck at what my next ...
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1answer
84 views

Can we compare the vapour pressure of solutions whose concentrations and temperature is known?

If we have some solutions, in which we know the temperature and concentration of the solute particles, can we compare their vapour pressures? Original question: Which solution has the highest vapour ...
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S(p)-C(p) vs. O(p)-C(p) overlap

In Grossman, The Art of Writing Reasonable Organic Reaction Mechanisms, he provides the following explanation. The question asks to explain why the difference in pKa values between PhSH and EtSH is ...

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