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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Molecular orbitals in an ionic diatomic compound

The wavefunction of a heteronuclear diatomic molecule, after the orbital approximation and the Born-Oppenheimer approximation, is $$\psi = c_A \chi_A \pm c_B \chi_B $$ where $\chi$ are the starting AO ...
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72 views

Relation of partial charge with wavefunction

Suppose we have an one electron system. The probability $P$ that electron's position is in some interval $x + dx$ is given by: $$P = \int_x^{x+dx}|Ψ(x)|^2 dx$$ So if we measure $N$ times the electron'...
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264 views

Solubility and covalent character [closed]

We have heard many times that this XYZ solute is soluble in this ABC solvent. But what does being soluble in mean in terms of bonding? What makes a compound soluble in some solvent and not in some ...
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Do different types of MOs have different occupancies?

There was a question in my textbook regarding the number of electrons in a molecular orbital. The maximum number of electrons in a sigma, pi, and delta molecular orbital are respectively? Now, I ...
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104 views

Why does sulphur exist in two forms in solid state, monoclinic and rhombic? Why in one favoured over another at a certain temperature and pressure?

Both Rhombic and Monoclinic sulphur consist of $S_8$ molecules packed together. Yet the former is more stable below $114^{\circ}C$ at 1 atm and spontaneously converts to monoclinic sulphur above that ...
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Why is it so difficult to crystallise anything in a glass capillary?

I'm talking about very fine glass capillaries with a diameter under 1 mm. I've found that if I carry out melting point analysis, the material in the capillary doesn't crystallise again. I did wonder ...
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2answers
112 views

What is the difference between mole and molar mass?

In my book it says 1 mole of carbon =1gram atom of carbon =12 gram if I see this relation that seems to me that 1 mole is mass of an atom In grams. But molar mass is different and why we use for ...
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3answers
611 views

Are coke (solid fuel from coal) and charcoal same thing obtained from different sources?

As coke is obtained from destructive distillation of coal, and charcoal from destructive distillation of substance other than coal (like wood and animal bones), are both the same thing, with charcoal ...
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1answer
183 views

How many atoms are there in single element? [closed]

Elements are chemical substances made up of the same types of atoms (atoms with the same proton number), whereas molecules are chemical compounds made up of atoms from two or more different elements. ...
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35 views

Aqueous glucose solution concentration computation

The question in my worksheet is as follows: You dissolve $\pu{1.451 mol}$ of glucose in water to a volume of $\pu{250 mL}$. The mass of the glucose is $\pu{261 g}$ and the molecular weight $\pu{180....
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Why is there preferential adsorption of a common ion during preparation of colloids by peptization?

There was a similar question asked here on Chem SE, but the answer was not very satisfactory to me, so I am asking a fresh question. Peptization is the process of creating a colloid from a precipitate ...
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Plotting second order reaction with different reactants

In a laser flash photolysis experiment, $\ce{C6H5NH2}$ $(C_0 = \pu{60 \mu M})$ is oxidize to its corresponding radical cations. There are three possible reaction pathways for the formation of the ...
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Isn't the change in Gibbs free energy for a reversible process zero?

In problem 6, part 6.5 of the 2020 IChO (PDF), a thermodynamic cycle is given for “one mole of monoatomic perfect gas”: $\mathrm{A \to B}$; isothermal reversible expansion receiving $\pu{250 J}$ by ...
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1answer
83 views

Justifying assumptions about method to find equilibrium pressure for co-existence of graphite and diamond

The standard state Gibbs free energies of formation of $\ce{C(graphite)}$ and $\ce{C(diamond)}$ at $T = \pu{298 K}$ are $\pu{0 kJ mol-1}$ and $\pu{2.9 kJ mol-1}$, respectively. The conversion of ...
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How do buffers work? and why only solutions of a weak acid and its salt with a strong base or vice versa work as a buffer [closed]

Please note that the definition of a buffer in my textbook is given as The solutions which resist change in pH on dilution or with the addition of small amounts of acid and alkali are called Buffer ...
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Do decomposition potentials change during electrolysis?

I was just wondering if decomposition potentials actually change during electrolysis. For example, if we reversed the Daniell cell reaction so that copper is oxidized, the half cell reactions would be:...
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1answer
54 views

What is the theoretical reason for the dependence of the surface tension on the alcohol concentration in water?

The qualitative sketches I, II and III given below show the variation of surface tension with molar concentration of three different aqueous solutions of$ \ce{ KCl, CH_3 (OH) }$and $ \ce{CH3(CH2)_{11} ...
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1answer
76 views

Total orbital angular momentum in a filled p subshell

From "Physical Chemistry", P. Atkins, J. De Paula, 9th edition, page 358 "A closed shell has zero orbital angular momentum because all the individual orbital angular momenta sum to ...
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Determining ion charge using rate constants and ionic strength

I am given the following data: The rate constant $k$ at $\pu{25 ^\circ C}$ in a reaction of persulfate ions and iodide ions in a water solution is assumed to vary with the total ionic strength of the ...
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1answer
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Calculating Gibbs free energy change when the state of ions is unknown

Problem Calculate $\Delta G^\circ$ for the following reaction: $$\ce{Zn(s) + Ag2O(s) + H2O(l) -> Zn^{+2}(aq) + 2Ag(s) + 2OH-(aq)}$$ Given $E^\circ_{\ce{Ag+/Ag}} = \pu{0.80 V}$, $E^\circ_{\ce{Zn^{+...
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Direction of spins in the singlet vs. triplet state

Suppose we consider the first excited state of the helium atom. We know that the first excited state of helium can exist as a triplet or singlet. The possible functions related to the spin of the two ...
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Deriving kinetic equations for reversible reactions

Problem Given the reaction $\ce{A <=>[$k_\mathrm f$][$k_\mathrm b$] B}$ with rate constants $k_\mathrm f = \pu{4E-2 s-1}$ and $k_\mathrm b = \pu{10^{-2} s-1}$. Initially, $\pu{2 mol}$ of $\ce{A}...
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1answer
80 views

Statistical entropy of perfect gas and indistinguishability

The weight, $W$ (the same $W$ as in Boltzmann formula $S=k\text{ln}W$) of a configuration {$N_0, N_1, N_2$, ...} is given by $$W=\frac{N!}{N_A!N_B!N_C!...} \tag{1}$$ where $N$ is the total number of ...
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30 views

Acid dissociation constant calculated from the ionization percentage

The question goes like this: An acid (HX) is 25% dissociated in water. If the equilibrium concentration of HX is $\pu{0.30 M}$, calculate the value of $K_\mathrm{a}$. So I tried as follows: if I ...
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97 views

How to find standard electrode potential of a reaction resulting from two different reactions?

Q1) Calculate $E_{\ce{Cu+}|\ce{Cu}}^o=E_o$. Given that- $E_{\ce{Cu^2+}|\ce{Cu}}^o=E_1$ and $E_{\ce{Cu+}|\ce{Cu^2+}}^o=E_2$ Method 1- $$(i)\quad\ce{Cu^2+} + 2e^-\to \ce{Cu} \quad... \Delta G_1=-2FE_1$...
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Quantitatively Calculate Dipole Moment [duplicate]

Recently, I have been reading up on articles relating to the dipole moments of different molecules (specifically this). I see how they can get bond lengths and experimental dipole moments with ...
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29 views

Is there a easy way to estimate how quickly something will dissolve depending on its surface area?

How exactly does the surface area of a solid for example a cube of sugar, affect the speed of its solvation. I guess everyone has observed that a batch of fine grounded sugar or salt dissolves much ...
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Can Amphotericin B cross a lipid bilayer membrane in its zwitterionic form when it is loaded in the aqueous core of a liposome?

Can Amphotericin B cross a lipid bilayer membrane in its zwitterionic form when it is loaded in the aqueous core of a liposome? Or must it be uncharged in order to cross the lipid bilyer membrane of ...
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Why is it that when dG°<0, dH°<0? [closed]

Let me preface this question by saying that I probably made a mistake somewhere. However, I can't figure out what it is. I was messing around with the Gibbs free energy equation to determine how the ...
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56 views

Density and partial pressure [closed]

A sample of $\ce{NOBr}$ gas was placed in a rigid flask where it decomposes at $\pu{25 ^\circ C}$ according to the following reaction: $$\ce{2NOBr(g) <=> 2NO(g) + Br2(g)}$$ At equilibrium, the ...
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Good sample references for TGA, DSC and DTA thermal analysis

I am trying to estimate kinetic parameters for my liquid decomposition using thermal analysis. After doing a literature survey, I have decided to use the following - thermogravimetry (TGA) ...
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1answer
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Why do we use external pressure to calculate work done by a gas in case of compression instead of using internal pressure? [closed]

According to formula work done is (Resisting pressure X dV)? Then in case of compression, isn't the resisting force is internal Pressure? Then why we the formula for compression is same as expansion ...
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1answer
90 views

Relation between standard silver-silver chloride electrode potential and solubility product of silver chloride

I learned that $E^\circ_\ce{Cl^-|Ag,AgCl}, E^\circ_\ce{Ag^+|Ag}$ and $K_\mathrm{sp}$ of $\ce{AgCl}$ are related as $$\boxed{E^\circ_\ce{Cl^-|Ag,AgCl} = E^\circ_\ce{Ag^+|Ag} + \frac{RT}{F}\ln K_\mathrm{...
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Why are protons more common than hydride ion?

I'm a high school student. I noticed $\ce{H+}$ ion is commonly present in my books while I didn't find any presence of $\ce{H-}$ ions in my books. However, I found on internet that $\ce{H-}$ also ...
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Why does magnesium have a greater ionization energy than lithium?

I'm a high school student and I'm learning about ionization energy and atomic radius of elements. I want to compare the ionization energy of lithium and magnesium. Here is the information provided in ...
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A liquid which climbs out of its pot [closed]

My Russian born wife recently asked me to buy her a skin remedy widely used in Russia. In English this is the oil of a plant called Sea Buckthorn. It is a thin yellow liquid. My wife put some of this ...
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1answer
84 views

Is this true for conductivity of mixture of two solutions equal to the sum of conductivities of each solution?

Suppose $\ce{Na2SO4}$ has a conductivity $\pu{2.6 \times 10^{-4} S cm-1}$ and on mixing $\ce{CaSO4}$ to saturation, the conductivity becomes $\pu{7.0 \times 10^{-4} S cm-1}$. So, Is the conductivity ...
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How to do a capacitively coupled electrode?

I have an AUTOLAB potentiostat: working electrode (WE, Pt wire), counter electrode (CE, Pt wire), reference electrode (RE, Ag/AgCl solid state). I would like to capacitively couple the potentiostat ...
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What is the explicit difference between ICT and PET for sensors?

I've been reading about boronic acid based sensors for saccharides (glucose, fructose, etc). Boronic acids are able to complex with diols to form boronate esters and if there is a luminophore on the ...
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1answer
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Can suspended solid particulate particles adsorb on surface?

Gaseous and liquid particles adsorb on solid surfaces. Can solid particles suspended in a fluid medium also adsorb on these surfaces in the same manner?
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Fields of Study in Chemistry [closed]

Is there a standard classification scheme for different areas of study and research for chemistry like mathematics has Mathematics Classification Scheme (MSC)?
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Does the vapor pressure of a substance depend on the presence of other gases?

The Clausius-Clapeyron equation (CC equation) can be used to find the (saturated) vapor pressure of a substance ie. the gas pressure at which the two phases (vapor + liquid or vapor + solid) reach ...
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Can a complex reaction have more than one rate determining steps?

I was solving some questions related chemical kinetics and encountered one question with multiple correct answer , the question is : For a complex (multistep) reaction, (a) the overall rate of ...
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1answer
45 views

What's the equilibrium pressure of CO2 gas over sodium hydroxide?

Many (too many) decades ago in physical chemistry lessons, I seem to recall that given the enthalpy changes of reactions, and maybe phase diagrams, one could work out what equilibrium a reaction would ...
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How practically to determine dispersion's Hamaker constant using CCC?

I know that Hamaker constants can be determined from CCC data. $$ccc=\frac{9.85 \cdot 10^4 \epsilon^3 k_B^5 T^5 \gamma^4}{N_A e^6 A^2 Z^6}$$ Where, $\epsilon$ is solvent dielectric constant, $N_A$ is ...
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Are pseudo-zeroth order reactions possible?

Are pseudo zeroth-order reactions possible? I have been taught that pseudo first-order reactions take place and they can be considered pseudo zeroth-order reactions because one reactant is in excess ...
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2answers
275 views

Is strength of pi bonds greater than sigma bond of nitrogen molecule?

I am referring to molecular orbital (MO) theory. In the nitrogen molecule (and elements of lower atomic number) $\textrm{sp}$ mixing occurs and the sigma orbital set is raised above the pi orbital set....
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1answer
167 views

Hessian matrix and mass-weighted Hessian eigenvalues

If I have the Hessian matrix and the mass-weighted Hessian matrix for a system, I can find the normal modes from the mass-weighted Hessian and the force constants from the Hessian. I have a list of ...
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1answer
74 views

Finding solubility of salts of polyprotic acids

Problem Given, for $\ce{H3PO4}$, $\mathrm{pK_\mathrm{a_1}=2.2}$ $\mathrm{pK_\mathrm{a_2}=7.2}$ $\mathrm{pK_\mathrm{a_3}=12.4}$ For the salt $\ce{Mg(NH4)PO4}$, $\mathrm{pK_\mathrm{sp}=12.6}$ and the ...
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35 views

Calculating electrons emitted when quantum yield is given

In a problem, the wavelength $\lambda$ of a monochromatic light, power $P$ of the source, and work function $\phi$ of the metal on which the light is shown is given. Quantum yield is $n$. I have to ...

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