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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12 views

Why in calculating 25 mM of Tris HCl the answer in gram is automatically refer to the gram in 1000 ml

In the lab class,my teacher told me that the answer i get in grams is automatically the grams in 1000 ml. Why is it possible without we doing anything the grams i get automatically the grams in 1000 ...
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How to calculate the temperature when equipartition is estimated [closed]

what must be the temperature be before the energy estimated from equipartition theorem is within 2 percent of the energy given. please help me to solve this. E= hcv/e^(bhcv)-1 v is the wavenumber is ...
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1answer
28 views

Does pressure affect rate constant? [duplicate]

I would like to know if pressure affects rate constant. Suppose pressure affects the rate constant. Does it depend on partial pressure (like: if I add an inert gas to the system), or only increasing ...
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41 views

Calculating pH of weak acid considering hydronium ions from water

In general to calculate pH of a weak acid , if we have $c$ concentration of acid initially then at equilibrium $\ce{H3O+}$ concentration is said to be $c$$\alpha$ , but I wanna ask that doesn't $\ce{...
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1answer
37 views

How much heat is lost to the calorimeter when hot water is mixed with cold? [closed]

If a student adds $\pu{100.00 g}$ of hot water at $\pu{50.00 °C}$ to $\pu{100.00 g}$ of cold water at $\pu{25.00 °C}$ and measures a heat change of $\pu{10707.37 J}$ for the hot water and $\pu{4778.86 ...
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49 views

Consequences of aluminum presence in rust removal electrolysis

I am using electrolysis to clean and remove rust from carbon steel parts. For the anode I use sacrificial carbon steel. For the cathode I use the steel part I am cleaning. The electrolyte is a ...
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Anti-Stokes percent [closed]

What are some examples of things that have a highest % of anti-Stokes scattering, (in Raman scattering?) (To clarify this is not a personal attack on Mr. Stokes, or anyone with the last name Stokes...)...
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27 views

Recycling flow if the chemical process of acetylene and hydrocyanic acid

I'm having some issues trying to solve this problem, because the concentration of inert in the recycling flow that I calculated is bigger that the concentration of the inert that is enterying to the ...
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26 views

Why are HOMO and LUMO energies invariant under spin-flip?

Atomic theory says singlet and triplet energies for the same orbital differ because of exchange interaction. However, molecular orbital (MO) theory describes the energy between the HOMO (highest ...
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Changing Variables in Thermodynamics

I have a question about changing variables in the context of thermodynamics, but I suppose this would extend to any set of variables that have defined and nonzero partial derivatives on a given set of ...
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Anionic surfactants sensitivity to hard water

It is known that anionic surfactants can be sensitive to hard water, as well that the sensitivity decreases according to their headgroup, where carboxylates are the most sensitive, followed by ...
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How do we actually calculate attraction and repulsion while explains bond length? [closed]

I am a high school student and in my textbook there is a figure given in which two isolated hydrogen atoms approaches each other and we define bond length as the distance between their nuclei at ...
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1answer
42 views

Calculating the electrode potential from thermochemical data (part 2)

This question is in continuation of this question. I am taking an example of $\ce{Cu^2+}$ in aqueous medium. $$\begin{align} \ce{Cu (s) &-> Cu (g)} & \Delta_\text{a}H^\circ &...
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28 views

Determine if an unknown solid is a covalent network structure or ionic solid by doing tests on it [closed]

What test could I run on the solid to find this out without melting/boiling it?
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25 views

When do activities need to be taken into account in the measurement of a pH? [closed]

pH is defined as $-log(a_{H})$, where $a_{H}$ is the activity of the protons, right? So in which cases is it not a good idea to approximate the pH by the concentration of protons?
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1answer
67 views

How does the rate equation account for solids and liquids?

The question is long because I wanted to include the whole thought process. Given the hypothetical reaction: $$\ce{ A(s) + B(aq) <=> C(aq) + D(aq)}$$ One would obtain the equilibrium constant: $$...
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Tracer Recovery in Analysis of Alpha Emitting Radionuclides

I am doing experiments analyzing the activity concentrations (Bq/kg) of several radionuclides and there is a small thing I don't quite understand how tracers work in the calculation of the activity ...
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How to calculate enthalpy of mixing for non-ideal solutions?

I have conducted a series of experiments where I basically mixed two solutions to form a non-ideal mixture and then I measured the temperature rise/fall (since both positive and negative deviation are ...
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1answer
39 views

Polarity of 1,2-dichloroethane [closed]

I don't understand how 1,2-dichloroethane is non-polar. Both the carbons have tetrahedral arrangements of atoms and I think there should be an overall dipole. Kindly explain why isn't there a net ...
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Is E° (HCl /H2) = E°(H+ /H2)? [closed]

Basically my question goes like this If we have to find E°(H2O/H2) . We consider the equilibrium of water with H+ and OH- E°(H2O / H2) = E°(H+/H2) + (RTln(Kw))/F . My question is going by this analogy ...
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1answer
67 views

How to identify an error in cut off filter (optical) usage when running spectrophotometry?

In spectrophotometry, often a cut off optical filter is used. With reference to a long-pass filter, which rejects any wavelengths outside a predetermined interval: low transmission in short ...
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1answer
45 views

Can use lead(II) oxide instead of lead(IV) oxide in car battery?

Question: If the discharge input equation $\ce{PbO2}$ is replaced by $\ce{PbO}$, will the battery still work? I think the product will not be water anymore but hydrogen gas. I am asking this question ...
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1answer
49 views

How does the boiling point of water inside a pressure cooker change with temperature? [closed]

My question is why a pressure cooker would affect the boiling point at all. To my understanding, the boiling point of a substance is defined by 'The temperature at which the vapor pressure of the ...
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60 views

Can we produce N-type semiconductors by using very high temperatures?

In the case of semiconductors in general, only a very thin layer of the wafer needs to be doped in order to obtain the desired electronic properties. The reaction conditions typically range from 600 ...
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107 views

Is a/b > 1 mol/L for a and b in the van der Waals equation?

We know that the van der Waals equation for real gases is $$\left(p + \frac{an^2}{V^2}\right)(V-nb) = nRT.$$ Is $a > b$ always in this equation? In my textbook $a > b$ for gases like $\ce{He},$ $...
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Is there any magnetic resonance spectroscopy that based on orbital angular momentum?

The different momenta of electron and nucleus are described by different quantum numbers. (a) l and m$_l$ describe the orbital angular momentum and quantization on its component along an arbitrary ...
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2answers
76 views

Why does magnesium hydroxide solution solidify after passage of time?

I have been trying to make a suspension of magnesium hydroxide in water. Around 40% magnesium hydroxide w/w. Initially it is fluid, but as time passes, it solidifies. What is causing this?
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47 views

Is the heat (or work) of the system always equal and opposite to that of the surroundings?

I know energy must always be conserved by the first law of thermodynamics, but is there ever a scenario in which a system say releases some amount of energy as work, and the surroundings gains equal ...
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44 views

Does the 1s orbital have two different phases? [duplicate]

How can the 1s orbital (in H atom for example) interfere both constructively and destructively (to give rise to bonding and antibonding molecular orbitals) with another 1s orbital, if the 1s orbital ...
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1answer
46 views

Hydrated electrons produced by radiation vs electrons from electrostatic charge: are they equally reactive?

One of the species generated in water or aqueous solutions by the ionizing radiations are free electrons that quickly become "hydrated" or "aqueous electrons" (see for example this ...
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1answer
94 views

Why is the Gibbs free energy of a reversible reaction not always 0? [duplicate]

From my understanding, reversible proceses are those where the expression: $$\Delta S_\mathrm{total} = \Delta S_\mathrm{system} + \Delta S_\mathrm{surroundings} = 0$$ is true for all for the entire ...
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porous silicon nitride for charge trapping flashs

When constructing charge trapping flashs, silicon nitride is preferably used to form the isolation layer to save/trap electrical charges. I wonder now when this isolation layer would be porous (in ...
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What is the name of the physical quantity that is given in kJ/g?

The chemical potential $\mu$ of a pure phase corresponds to the Gibbs free energy $G$ divided by the amount of substance $n$: $${G\over n} = \mu,$$ so the units of $\mu$ are $\pu{kJ mol^-1}.$ What do ...
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1answer
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Chemical equilibria - Lab practical [closed]

In an experiment to determine the partition coefficient, how would we assure that the system has reached partition equilibrium?
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96 views

Can an elementary reaction have zero order?

I am very confused right now about my approach to this question could somebody help me out with this. I reasoned my answer as given below Let's assume if a complex reaction is of zero order. It ...
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Enthalpy/Temperature change in a chemical reaction

I was wondering how exactly absolute temperature change in a chemical reaction could be calculated. For example, consider this reaction: 3H₂+N₂→2NH₃, ΔH=-46kJ/mol (298.15K) Assuming the given reaction ...
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Is dehydration of cobalt(II) chloride hexahydrate dynamic equilibrium?

I know that the dehydration of cobalt(II) chloride hexahydrate is a reversible reaction, is it a dynamic equilibrium? $$ \begin{align} \ce{CoCl2·6H2O &<=> CoCl2·2H2O + 4 H2O}\tag{R1}\\ \ce{...
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Standard Enthalpy of formation

The definition says The standard enthalpy of formation is defined as the change in enthalpy when one mole of a substance in the standard state (1 atm of pressure and 298.15 K) is formed from its pure ...
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1answer
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How rate of absorption remains same throughout the process?

While reading surface chemistry, I got Rate of adsorption is high at begining and then decreases till equilibrium is attained . On the other hand , rate of absorption remains same throughout the ...
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The necessary energy required to ionize 1g of potasium in its fundamental state if the ionization energy is given

The energy of ionization of the potassium is $\pu{6.94\cdot 10^{-19} J/atom}.$ Find the necessary energy to ionize $\pu{1 g}$ of potasium that is found on its fundamental state. Attempt. I really ...
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Chemical Equilibium [Equilibrium Constant] [duplicate]

During heterogenous equilibrium, we take active mass of pure solids and liquids as 1. I don’t understand what is meant by pure liquids here. Please guide me how to write equilibrium constants in these....
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45 views

Comparing average radius of subshells for multielectron atoms

I recently came across a question comparing the average radius of subshells. A search on the internet gave the following result for single electron atoms: $$\langle r\rangle_{n,\,l}=\frac{a_0 n^2 \...
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36 views

Dry ice sublimation rate in water

As I got some a finger sized of dry ice in water, it started to bubble vigorously as expected and gave off a lot of smoke. But after 3 minutes or so, the rate of sublimation seems to slow down a lot, ...
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1answer
101 views

How to derive formulas for n factor of different types of reactions?

While studying Redox reaction, I came across this term called n-factor which seems to me as a short-cut trick to do the questions quickly. Since I am preparing for a competitive exam so our chemistry ...
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23 views

Vapour pressure and boiling [duplicate]

I have come across two definitions for boiling point: It is the temperature at which a liquid gets vaporised It is the point where vapour pressure = external pressure How are they related? How does ...
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39 views

A gaseous mixture contains hydrogen atoms in the 4th excited state and helium ion; spectral lines emitted when all these return to the ground state

A gaseous mixture contains hydrogen atoms in the 4th excited state, $\ce{He^+}$ ions in 3d excited state, and $\ce{Li^{2+}}$ in 2nd excited state. Find the number of distinct spectral lines emitted ...
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Is the cell in an isothermal titration calorimeter open to the atmosphere? [closed]

I'm just trying to understand how they can model an isochoric process.
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41 views

Does a larger bond energy in reactants mean a more exothermic reaction?

In the book "Combustion Physics" for C.K Law, page 42, it is stated that: The parameter that has the next strongest influence on [adiabatic flame temperature] $T_{ad}$ is the $C/H$ ratio of ...
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42 views

What determines the coefficient B in the Bell-Evans-Polyani equation?

From the Bell Evans Polanyi principle, $E_a = A + B \Delta H$. How is the $B$ coefficient determined? This is my thinking: For exothermic reactions (where the transition state resembles reactants more ...
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29 views

Number of gas molecules in activated state vs normal state

I have a simple bimolecular reaction $$\ce{A + M <=>[k_2][k_1] A^* + M}\tag{1}$$ where $\ce{A}$ is a molecule which collides with another molecule $\ce{M}$. $\ce{A^*}$ is the $\ce{A}$ molecule ...

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