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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3 votes
3 answers
111 views

How is the entropy of mixing related to chemical reactions in solution?

When calculating the Gibbs energy of reaction for reaction mixtures at arbitrary concentrations, you use the following expression: $$\Delta_\mathrm r G = \Delta_\mathrm r G^\circ + RT\ln Q$$ The term $...
0 votes
1 answer
48 views

Differential equation in consecutive reactions

I'm blocked in a step of getting to the equation $(7)$, more precisely in the step between $(5)$ and $(6)$. I show my way to solve it down, but I don't get the same as $(6)$, so I wanted to know if I ...
6 votes
1 answer
68 views

Iodine clock reaction: lower temperature but faster result?

I was told by several high school students that they experienced odd results in their iodine clock reaction lab. They did several different trials, and the lower the temperature, the faster the blue ...
2 votes
1 answer
85 views

Photoelectric effect: What happens when you irradiate the metal strip with a wave of frequency exactly equal to threshold frequency of the metal?

My teacher said that if we irradiate the metal strip (used in generating the photoelectric effect) with light having frequency equal to the metal's threshold frequency, then the electrons will have ...
1 vote
1 answer
29 views

Why the electronic configuration of samarium is ending with 4f⁶6s²

What is coming in my mind is that 4f^7 6s^1 should be more stable as it allows two orbitals to be half filled rather than 4f^6 6s^2 in which only one orbital is completely filled....can someone please ...
0 votes
0 answers
14 views

Surface-Plasma Interaction Education Guidance

I work in a field where understanding interactions between plasmas and metals for the purpose of generating a particular reaction is important. However, I know very little about plasma assisted ...
1 vote
1 answer
1k views

Electrochemistry molar conductivity

Molar conductivity increases with decrease in concentration. This is because the total volume, $V$, of solution containing one mole of electrolyte also increases. It has been found that decrease in $\...
-2 votes
1 answer
74 views

What do the positive and negative signs on the atomic orbitals diagram imply? [closed]

I was reading up on wave functions and electrons behaving like a wave when they are bound in an atom. In the orbital diagram, the + and - signs don't make any sense to me, and the reasoning that one ...
2 votes
2 answers
171 views

How can I model cellular membranes in terms of topology?

I'm reading from Principles of Physical Biochemistry by Kensal E van Holde (1998-01-06) in order to review some biochemistry and work my way toward a more mathematical approach to understanding ...
2 votes
1 answer
84 views

What is the reason for decomposition of layered cathode materials?

Zhang [1] and related publications claim oxygen can evolve from layered metal oxide cathode materials when charging the Li-ion battery. Is it the high positive potential given to the cathode while ...
1 vote
1 answer
5k views

Specific conductance of 0.1 M acetic acid

Find specific conductance of $\pu{0.1 M}$ acetic acid given that its molar conductivity is $\pu{4.6 S cm^2 mol^-1}$. I used the formula $\Lambda_\mathrm m = \kappa/c$, where $\Lambda_\mathrm m$ is ...
-5 votes
0 answers
22 views

Are there things with different physical attributes that serve exact same purpose in a system? [closed]

I’ve been puzzling about this cross-disciplinary concept for the last week. Can you think of any two things that have different physical make up that serve the exact same purpose? For instance, ...
1 vote
0 answers
48 views

Why is it impossible to determine number of visible emission spectrum of He+

We know that atoms emit spectral lines on excitation and de excitation. I was doing one high school question based on this theory Number of visible lines when an electron returns from 5th orbit upto ...
4 votes
2 answers
82 views

Required induction time for steady-state approximation to hold

In chemical kinetics, since we often have to deal with complex reactions, approximations are introduced in order to make the calculations easier. A widely used simplification is the steady state ...
-2 votes
0 answers
33 views

Steel Composition Graph [closed]

Dear all, regarding the hypereutectoid steels, why does it stop at 2.14 and not 6.7? Thank you
3 votes
1 answer
145 views

Negative or fractional order of reaction

Let $\ce{A}$ be the reactant and $\ce{P}$ the product at the imaginary elementary reaction $\ce{A->P}$. Could it possibly have a net total order of $-1?$ $$-\frac{\mathrm d[\ce{A}]}{\mathrm dt} = k[...
0 votes
1 answer
30 views

Comparing the enthalpy change between the formation of water in two states

The enthalpy of the reaction $\ce{H2(g) + 1/2 O2 (g) -> H2O (g)}$ is $\Delta H_1$ and that of $\ce{H2(g) + 1/2 O2 (g) -> H2O (l)}$ is $\Delta H_2$. Then, a) $\Delta H_1 < \Delta H_2$ b) $\...
8 votes
1 answer
20k views

What does a fractional order of reaction mean for the mechanism?

I'm doing a high school/sixth form college investigation of the kinetics between magnesium ribbon and hydrochloric acid. I have obtained a rate order was $1.5$ with reference to $[\ce{H+}]$ and hence ...
-2 votes
1 answer
80 views

How does adding oxalic acid to water change the volume of the solution?

Does $\pu{87.4 mL}$ of $\ce{H2O}$ and $\pu{12.6 g}$ of $\ce{HOOC-COOH.2H2O}$ create $\pu{100 mL}$ of a solution? So in our practical class our teacher wanted to make $\pu{100 mL}$ $\pu{1 M}$ aqueous ...
2 votes
1 answer
553 views

How is it Possible to Measure Electrode Potential?

It is known that potential difference on metal/electrolyte or any kind of interphase can't be measured since voltmeter needed to measure it is made of metal which would in contact with metal and ...
-2 votes
0 answers
19 views

Effect of number of moles on equilibrium constant [closed]

In Habers process for example we know that 2 moles of n2 react with 3 moles of h2. Will the equilibrium constant remain same if I use 1 mole of n2 and 1 mol of h2. If yes, then why do questions give ...
7 votes
0 answers
138 views

Mathematical models of oscillatory chemical reactions

I am a mathematician working on real-life models in ordinary differential equations. I want to know if there are any models of oscillatory chemical reactions that consist of three ordinary ...
4 votes
0 answers
49 views

How exactly thermal infrared (e.g. FLIR) cameras image methane leaks? Are they measuring a temperature difference or an emissivity difference or...?

The story Infrared camera shows the impact of vehicle emissions says: In an effort to visually demonstrate the potentially fatal impacts of air pollution, FLIR Systems (Wilsonville, OR, USA; www.flir....
0 votes
1 answer
121 views

Cubic nature of van der Waals' gas equation

$V_m^3-\dfrac{RT+bP}{P}V_m^2+\dfrac{a}{P}V_m-\dfrac{ab}{P}=0$ So, At $T<T_c$ the above equation has three real roots say $V_1,V_2,V_3$, my doubt is what does this mean physically because for some ...
1 vote
2 answers
87 views

Half-life of a reversible first-order reaction of the form A ⇄ B

I am wondering if the half-life of a reversible first-order reaction of the form $\ce{A <--> B}$ is defined as the time in which half of the amount of reactant which should react up to ...
-3 votes
0 answers
14 views

Why volume is not additive property [duplicate]

Imagine there is container of volume 10L and I filled it with some liquid (we don't know volume of liquid but it looks like it completely fills the container). In the same container I have added ...
-4 votes
0 answers
37 views

Reaction of glycerine with formic acid? [closed]

How to make glycerol react with formic acid? Maybe someone has experience with the experimental parameters etc.. What are the reaction products and what is the best way to detect them?
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3 votes
2 answers
7k views

What is the relation between absolute temperature, and rates of diffusion and effusion of a gas?

According to Graham's diffusion law, rate of diffusion is directly proportional to square root of temperature but rate of effusion is inversely proportional to square root of temperature. Why is this ...
2 votes
1 answer
162 views

Why does the heat of formation of organic radicals and positive ions decrease with their size and degree of branching at the radical or ionic site?

I am currently studying the textbook Mass Spectrometry, third edition, by Jürgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following: The heat of formation ...
8 votes
4 answers
377 views

How can we replace volume in ideal gas equation with V - nb?

We know that ideal gas equation is $PV= nRT$ where P is the pressure of the ideal gas and V is the volume of the ideal gas. Thus, we can write : $$ P_{\textrm{ideal}}V_{\textrm{ideal}} = nRT$$ Now ...
3 votes
4 answers
2k views

What happens to a greenhouse gas after it absorbs infrared radiation?

We say that a greenhouse gas increases the temperature of the surface of the earth but how does it do that ? Only by re emitting the absorbed IR towards the earth ?
3 votes
2 answers
80 views

Why is radial probability density exactly zero at the center?

I have read that the radial probability density is exactly zero at $r = 0$ because the radial probability density is $$P(r) = \psi^2\,\mathrm dv,\tag{1}$$ where $\mathrm dv$ is the volume of spherical ...
0 votes
1 answer
34 views

Why is the excluded volume in van der Waals 4 times the actual volume of the gas molecule?

I am having trouble understanding why the excluded volume of a particle is four times its actual volume. According to Wikipedia, "The excluded volume b is not just equal to the volume occupied by ...
3 votes
1 answer
169 views

Why does confinement of quantum dots result in discrete energy levels?

I'm doing a project with lead (II) sulfide quantum dots because they have optical transitions in the near infrared. I understand the simple "particle in a box" approach where confinement strengthens ...
0 votes
0 answers
44 views

What is the meaning of k,l,m,n in this second quantized hamiltonian?

The following is a screenshot from chapter 8, by Wouters et al, titled "Five Years of Density Matrix Embedding Theory", in the book "Fragmentation: Toward Accurate Calculations on ...
0 votes
0 answers
30 views

How can I calculate average interatomic distance between all identical elements in supercell?

Good afternoon! Maybe someone came across, I want to know the average interatomic distance between all identical elements in some supercell. In Vesta or a similar program, it shows only one piece at a ...
3 votes
1 answer
142 views

Which solvent is good for using SU-8 particle in Optical tweezers?

I'm studying Optical tweezers. I've used Polystyrene for samples. Nowadays, I've got SU-8 pillar. I wanna use that for sample, but its density is heavier than water. I can't use that. So I wanna know ...
6 votes
1 answer
2k views

Confusion regarding calculating the pH of a salt of weak acid and weak base

I need to calculate the $\mathrm{pH}$ of a salt of weak acid and weak base in an aqueous solution. Method I used for calculation For a salt of a weak acid and a weak base (assuming complete ...
0 votes
0 answers
28 views

Multiplicity of a transition state undergoing a six electron movement

How to specify the multiplicity for the transition state of a molecule undergoing a Cope rearrangement? I've read that one could technically approximate the transition state (TS) as a diradical, but ...
0 votes
1 answer
187 views

What is the proof of Kohlrausch's Law of Independent Migration of Ions? [closed]

What is the proof of Kohlrausch's Law of Independent Migration of Ions? How did Kohlrausch calculate the limiting molar conductance of a weak electrolyte? I am asking this in context of ...
1 vote
1 answer
46 views

Serial reactions or consecutive reactions: rate vs time

Serial reactions, or consecutive reactions, are two or more reactions in which the product of the first reaction becomes the reactant in the next. The simplest case of a serial reaction involves a ...
0 votes
0 answers
33 views

Why does a double-bonded nitrogen molecule have more than twice the bond (dissociation) energy of a singly-bonded one?

If the first bond between atoms is (usually) stronger than the second one, and the second one, in turn, a bit stronger than the third, how does a doubly-bonded nitrogen molecule have more than twice ...
0 votes
1 answer
46 views

Degree of dissociation and conductance

My book says ratio of molar conductance at a given concentration of solute and molar concentration at infinite dilution is equal to degree of dissociation for weak electrolytes. I understand it ...
-1 votes
0 answers
27 views

Supersaturation [duplicate]

We know there is upper limit on solubility of most things like sugar in water. I want to know what is the reason behind this. I understand that number of molecules getting dissolved equals number of ...
-3 votes
1 answer
47 views

What does it mean when we say an atom has infinite energy levels/shells? [closed]

My chemistry teacher told that an atom has infinite energy shells according to Bohr model , where electron reside according to its angular momentum and energy. But in lower classes/ grades I have ...
1 vote
0 answers
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Compute the energy of carbon atom with Molpro [migrated]

I have been learning some basics of molpro and quantum chemistry, however I am deeply confused now. As a very simple example, I want to compute the energy of a carbon atom using D2h group For its ...
2 votes
1 answer
46 views

Rate law for thermolysis at temperatures well above the decomposition temperature

If the temperature is higher than the decomposition temperature, are thermal decomposition reactions reversible? For example, which of the following schemes would be more appropriate for temperatures ...
2 votes
0 answers
34 views

At constant solvent activity, do solution properties depend on identity of the solute?

When a substance is dissolved or mixed with water in high concentrations, the activity of water drops from 1 to a value that depends on the substance and its concentration. Is it correct to say that ...
4 votes
1 answer
5k views

How does Aloe Vera leave a cool feeling on your skin? Why does it evaporate fast?

If you have ever grown Aloe Vera and applied it to your skin, it feels a bit slimy. However, after it evaporates it has a cool feeling on your skin. Also, why does the Aloe Vera evaporate so fast? ...
10 votes
3 answers
3k views

What kind of equilibrium constant we use for Gibbs free energy and Van't Hoff equation?

We know that the Gibbs free energy is related to the equilibrium constant by the following equation: $$\Delta_\mathrm{r}G^\circ=-RT\ln K$$ We also know the Van't Hoff equation: $$\ln\left(\frac{K_2}{...

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