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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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1answer
39 views

Meaning of polarization pulse in microwave (rotational) spectroscopy

In the recent rotational spectroscopy literature, "microwave polarization pulse" is often used in conjuction with pulsed Fourier transform microwave spectroscopy (Google Scholar). Sometimes the pulse ...
6
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1answer
57 views

Why is the graph of fluorescence vs. wavelength continuous?

If the emission of a photon from an excited state to the ground state occurs with a precise energy, then why is it that wavelengths that differ from lambda max have values on a fluorescence vs. ...
10
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2answers
759 views

Can the van der Waals coefficients be negative in the van der Waals equation for real gases?

A gas described by van der Waals equation has the pressure that is lower than the pressure exerted by the same gas behaving ideally. True or false? My approach $$P(\text{ideal}) = P(\text{real}) + P(...
2
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1answer
77 views

Derive expression for heat flow from oil bath to metal sphere

A spherical ball of iron is put into a hot bath of oil. The iron ball is initially at a low temperature and heat transfer from the oil to the iron will increase the temperature of the iron ball. ...
1
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0answers
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-...
0
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1answer
80 views

Relationship between rate of reaction and pressure

Given the equation $$\ce{A(g) + B(g) → C(g) + D(g)}$$ with reaction rate given by $$v = k[\ce{A}]^2$$ How can I prove that reaction rate goes up with pressure? I tried substituting $k$ for $Ae^{-...
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0answers
43 views

How will the equilibrium concentration change on adding inert gas at constant pressure? [duplicate]

The given reaction is $$\ce{AB2(s) → A(g) + B2(g)}$$ Now on adding inert gas at constant pressure equilibrium should shift on direction of more gaseous moles. But the answer says that equilibrium ...
2
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0answers
46 views

How to obtain spectroscopic constants Omega_e, Alpha_e, B_e, D_e and D_0 from centrifugal constants?

I need to compute a spectroscopic constants of $N_2^+$ states and I would like to do it using LEVEL16 software, due to its high interpolation flexibility. But it seems, that LEVEL16 can only compute ...
-3
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1answer
114 views

Questions in Equilibrium [closed]

I have two inquiries concerning equilibrium: Does $K_c = 5.0$ indicate that the equilibrium mixture contains both products and reactants at an approximately equal amount? I know that $K_c \approx 1.0$...
4
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1answer
232 views

Electrolysis of water: Which equations to use? (IB Chem)

There is a list of standard electrode potentials at 298 K from the p. 23 of IB Data Booklet 2016. Which of the following equations (forward/backward reactions), from the two possible ones involving ...
2
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1answer
79 views

Proving a relation for fugacity of component i in term of independent variables (T,V)

In Molecular Thermodynamics of fluid phase equilibria by Prausnitz et al. [1] the authors recommend to use the following equation which gives the fugacity of component $i$ in terms of independent ...
4
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0answers
51 views

Why do old black and white photos fade?

I understand why photos based on organic dyes would fade (discussed previously). But photos based on metallic silver fade as well such as like the one shown below. As a metal (a fairly stable one at ...
0
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1answer
103 views

Maximum number of atoms in the ground state

I was given the following question. A sample contains $100$ identical and hypothetical $H$-like atoms ( $Z$ may be fractional). Out of the given atoms, some are in the ground state, while others ...
6
votes
2answers
114 views

Scientific Reason for Salt Solution Gaining Volume

A little background to this question: my mom placed a glass with salt and enough water to just cover the salt in a room to "absorb negative energy" out of the room at her office. It obviously "worked"....
2
votes
1answer
197 views

Gibbs Free Energy and Maximum Work

I am a high school student and my professor mentioned that the Gibbs free energy is the maximum amount of work (or useful work) that a system can do, whereas entropy is a measure of the non-available ...
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0answers
30 views

Hydrogen peroxide and carbon as hybrid rocket propellant?

I was thinking that a hybrid rocket could be made using hydrogen peroxide and activated charcoal or some other carbon source. Step 1: Decompose hydrogen peroxide to steam and oxygen, as in a ...
1
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2answers
100 views

Why is reduction potential of water ( 2H₂O + 2e⁻ → H₂ + 2OH⁻ ) is -0.83 insted of 0, as in the case of (2H⁺ → H₂)?

I came across this value of reduction potential of water while solving a question. Also, I noticed that, for example $$\ce{Ag+ → Ag}$$ has a fixed standard potential, and the same is used when we do ...
14
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3answers
3k views

Is it possible to boil a liquid by just mixing many immiscible liquids together?

In open air, when vapour pressure reaches 1 atm, boiling takes place. I read that if we add two immiscible liquids together, the total vapour pressure of the 'mixture' is close to $p = p^*_A + p^*_b$,...
1
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0answers
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?
1
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1answer
164 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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0answers
166 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_\...
2
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2answers
116 views

Oxidation of metals/halogens by oxygen gas in acidic aqueous solution

I had some confusion about the correct answer to the following question: Which substance can be oxidized by $\ce{O2(g)}$ in acidic aqueous solution? Two of the answer choices were metal cations (...
2
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2answers
102 views

Which substances have the highest/lowest enthalpy of formation per gram?

Which substances have the most extreme enthalpies of formation per gram at standard temperature and pressure?
2
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2answers
620 views

Compressibility Factor Of Gases

In the general equation of the compressibility factor $Z$, we define $Z$ as $$Z=\frac{pV}{nRT}$$ Here, what is $p$? Is it $p_\text{real}$ or $p_\text{ideal}$? Also, what is $V$? $V_\text{real}$ or $V_\...
0
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1answer
90 views

Gravimetric analysis

In a gravimetric determination of phosphorus an aqueous solution of dihydrogen phosphate ion is treated with the mixture of ammonium and magnesium ions to precipitate magnesium Ammonium Phosphate. ...
7
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1answer
337 views

Only d orbital electrons for spin only magnetic moment

During my chemistry lessons and self studies, I have come upon many instances where I observed that during calculations of spin only magnetic moment of transition elements only the d orbital electrons ...
1
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2answers
77 views

Is Gibbs energy change during osmosis positive? If so then why is it spontaneous?

For ideal solution, μA=μA* +RT lnxA ln function is an increasing function, means that the higher the xA the higher the μA......(1) Now consider osmosis. From Atkins' Physical Chemistry Ninth ...
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0answers
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 ...
0
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1answer
37 views

Finding simplest formula of a compound with following specifications

I ran into the following problem, wherein I'm asked to find the simplest formula of a compound containing $50 \%$ of element $X$ (atomic wt. 10) and $50\%$ of element $Y$ (atomic wt. 20). I know ...
2
votes
1answer
42 views

What are we seeing in this AC salt-water copper-wire experiment?

There's a highly watched video on YouTube by "ElectroBoom" on the effects of passing AC (not DC) current through salt water. The water gets cloudy and at the end of the video we can see one of the ...
0
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0answers
41 views

Relation between size and lattice energy

I came across the statement “BeO and MgO have high melting point because of the lattice energy of BeO and MgO is appreciably high due to their small size” in my mAterial I didn’t understand what ...
1
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1answer
98 views

Is temperature of crystallisation same as melting point temperature for polymers?

Melting point tends to be a temperature range. Is it true that the temperature of crystallisation is the highest temperature at which the polymer melts and thus there is some distinction between ...
1
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1answer
396 views

Heat of formation of aqueous H⁺

In my book it is given that by convention heat of formation of aqueous $\ce{H+}$ is taken to be zero. Heat of formation is energy released or absorbed when 1 mole of a compound is formed from its ...
0
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0answers
42 views

Derivation of equilibrium constant [duplicate]

In general chemistry, we learn that the equilibrium constant, defined in terms of activities, for the reaction $$\ce{aA + bB -> cD + dD}$$ is given by $$K_\mathrm{eq} = \frac{(\ce{C})^c(\ce{D})^...
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0answers
42 views

For azeotropic mixtures, is the total vapour pressure at equilibrium equal to the partial pressure of one of the components?

I know, a ridiculous statement. But here's how I reached at it . Say we have a solution of two components liquids A and B. By Raoults law, $$p_A= p_A^o \times x_A \tag1$$ Also by Dalton's law, $$...
2
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3answers
182 views

Changing the order of the reaction with change in concentration

The reaction $$\ce{2 A + B + C -> D + 2 E}$$ is found to follow the rate law as $$r = k[\ce{A}][\ce{B}]^2[\ce{C}]^0$$ If the concentration of $\ce{A}$, $\ce{B}$ and $\ce{C}$ increases two times ...
2
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0answers
31 views

Perturbation theory for molecules, chromophore group, dipole approximation,

I am interesting in chromophore group and dipole approximation. For example, i have a molecule (acetone or any other ketone/enol) which is belongs to some symmetry group. Because of the symmetry ...
1
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2answers
97 views

What happens to the pressure of gas when only one molecule of it is placed in a very large container?

We say that pressure due to gas is constant throughout the container. Pressure is created by molecules present in it. When there are many molecules I agree that they can apply the same pressure all ...
2
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0answers
135 views

What is the ideal temperature and pressure to crack water?

Using sun mirrors and solar cells for electricity. What temperature, pressure and voltage ideal for cracking water. Source: NPR Source Would it take more or less electricity to crack water under ...
2
votes
1answer
223 views

Why is $1s-1s$ orbital overlapping stronger than $2p_x-2p_x$ orbital overlapping?

Assume the x-axis to be the internuclear axis. Hence, both $1s-1s$ and $2p_x-2p_x$ will form $\sigma$ bonds. Also consider the fact that $p$ orbitals have more directional characteristics. Given the ...
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0answers
32 views

What is the reasoning behind deriving electrode potential of a metal-metal sparingly soluble salt electrode?

Considering a sparingly soluble salt $M_xN_y$ of the metal $M$, in which the corresponding reaction is $M_xN_y$ = $xM^{y+}$ + $yN^{x-}$, the standard electrode potential is given by $E^{o}_{M_xN_y/M/...
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1answer
70 views

Getting pH of a weak acid and conjugate base with a given ratio [closed]

A practice question reads What is the $\ce{pH}$ of a solution of a weak acid and its conjugate base when the ratio of the concentrations of the conjugate base/weak acid is 1/3? (the weak acid $K_\...
5
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1answer
746 views

Calculating entropy change: reversible vs irreversible process

Since the change in internal energy and enthalpy, which are equal to the heats for a constant-volume and constant-pressure process, respectively, are state functions, the heats for a reversible v.s. ...
-1
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1answer
58 views

Electrons in methane [closed]

Why does a molecule of methane have 10 electrons? I used to think that the number of electrons in methane were 8 in number but it turns out that there are 10 in number but i dont know why. Please ...
0
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0answers
21 views

What are the activation energies for the combustion of RP-1 with liquid oxygen, and UDMH with Dinitrogen tetroxide?

I need to compare the chemical and physical properties of the two reactions for a school project. However, I can't find a source that explicitly states their activation energies! We haven't learned ...
6
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1answer
113 views

Are electronic descalers a scam?

It seems there are some electronic kits sold around nowadays by major retailers (e.g., Home Depot and Amazon) claimed to remove built-up scale from water pipes. But, do they actually work? If so, ...
1
vote
2answers
124 views

Determining Kc for the equilibrium involving iron thiocyanate using spectrophotometric data

$$\ce{Fe^3+(aq) + SCN-(aq) <=> [Fe(SCN)]^2+(aq)}$$ $\pu{12.0 mL}$ of $\pu{0.00110 mol L-1}$ $\ce{Fe^3+}$ was added to $\pu{6.00 mL}$ of $\pu{0.00140 mol L-1}$ $\ce{SCN-}$. The absorbance of ...
2
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0answers
16 views

Why do electrocatalysts based on polyoxometalates and carbon materials have a weaker activity/performance in acidic media?

I am testing now some doped N and S doped carbon nanomaterials alone and immobilized in POM for the purpose of developing a nanocomposite that can serve as an electrocatalyst for energy-related ...
0
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0answers
24 views

how does mass of carbon 12 is like this? [duplicate]

1u is defined as per carbon 12 so 1 atom of c have 6 neutrons and 6 protons both having mass more than 1u (Google)so total mass of carbon 12 is more then 12u (also there would be some mass of ...
1
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0answers
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 ...