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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78 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 ...
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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"....
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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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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 ...
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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 ...
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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 $p = p^*_A + p^*_b$,...
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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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80 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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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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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 (...
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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?
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211 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_\...
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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. ...
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189 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 ...
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72 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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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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32 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 ...
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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 ...
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25 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 ...
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48 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 ...
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1answer
71 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 ...
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41 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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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, $$...
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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 ...
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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 ...
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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 ...
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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 ...
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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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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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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_\...
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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. ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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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What are the reasons that make platinum a good electrocatalyst for oxygen reduction reaction? [duplicate]

Researchers are trying to find new electrocatalysts for energy related reactions in fuel cells in order to replace the expensive platinum-based materials. I would like to know what are exactly the ...
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49 views

Hydrolysis and Hydration

Does Ammonium Acetate, a salt of a weak base and weak acid, undergo both hydration and hydrolysis in aqeous solution? What is meant by the statement that " Some hydration reactions are hydrolysis"
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125 views

Equilibrium constant for esterification process

Teacher told us that the concentration term for pure liquids and solids is always $1$. But online I found this reaction: $$\ce{CH3COOH(l) + CH3CH2OH(l) <=> CH3COOCH2CH3(l) + H2O(l)}$$ ...
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No sign flipping while figuring out the emf of voltaic cell?

I learnt that for a voltaic cell, the value for the $E_\text{cell}^\circ$ when the reaction is spontaneous is given by $$E_\text{cell}^\circ = E_\text{cathode}^\circ - E_\text{anode}^\circ, \label{...
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165 views

Gibbs free energy of formation vs. Gibbs free energy of reaction?

Consider the following reaction: $$\ce{A(s) + B(s) <=> AB(s)}.$$ I know there might be kinetic limitations but I am only interested in thermodynamic relations. In general, the Gibbs free ...
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Should I include ions from the solvent in solubility product constant calculations?

I'm trying to determine the Solubility Constant $K_\mathrm{sp}$ of $\ce{Ba(NO3)2}$ dissolved in nitric acid solution $\ce{HNO3}$ from experimental data. $\ce{HNO3}$ will be mostly dissociated so ...
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63 views

Why is nucleus charge squared in Rydbergs formula?

According to coulumbs law, the energy changes linearly with charge. So why is the nucleus charge squared in this formula? Is there a way to derive it? I was suspecting it might be because it pulls ...
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56 views

Can a solute be physically filtered out of a solvent?

Suppose that I have a substance dissolved in water. I then pour the solution into a filter. The filter's pores are large enough to allow the passage of water, but not the passage of the substance. In ...
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What is the ANO-RCC basis set and how does it work?

On the basis set exchange, the ANO-RCC basis looks huge, even for hydrogen: ...
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54 views

Trend in ionisation potential in period 2

Carbon has valence electronic configuration of $2s^2$ $2p^2$. Beryllium has configuration $2s^2$.So carbon should have less ionisation potential than Beryllium as it is easier to remove electrons from ...
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110 views

Find out of the friend is getting a good deal [closed]

I have a strange chemistry question that I've never came across before, and I have no idea about how to solve it. Your friend comes across a good deal to purchase a gold ring. She asks you for ...
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Which ions determine ionic conductivity of a salt solution?

Let's take $\ce{ZnSO4}$ salt solution in water for example. So the ions inside my solution will be $\ce{H+}$, $\ce{OH-}$, $\ce{Zn^2+}$ and $\ce{SO4^2-}$. My questions are: Is the ionic conductivity ...