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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24 views

T∆S implies that heat flows which way?

From Schroeder's Introduction to Thermal Physics. Parts $(a)$ and $(b)$ are quite simple, and we find that $ \Delta H =-2808\ \mathrm{kJ}$ and $\Delta G =-2879\ \mathrm{kJ}$, so by $\Delta G = \Delta ...
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Indicators used in Titration [duplicate]

I want to know everything in detail about Indicators used in titrations, their structure,pH range. Please suggest me a book for it.
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2answers
557 views

What is “atomic feeling”?

The Avogadro project, an effort prior to the recent redefinition of Avogadro's constant to design a nearly perfect sphere of silicon-28, apparently relied on the fine fingers of optician Achim ...
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What matters most when attempting to achieve the highest efficiency water electrolysis, voltage, current or resonant frequency? [closed]

I recently constructed a rudimentary water electrolyzer using some homemade electrodes and PVC pipe. I have read much about electrolysis and how it works, but I am still left with many questions. I am ...
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In “Organic Chemistry” We often see the reagent aqueous NaOH .What is the approximate range we can say of this so called aqueous NaOH? [closed]

For example, in coupling reaction we often see that we write aq. NaOH, but since it depends upon pH scale, so what's the approximate range of aq. NaOH.
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1answer
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Ammonia decomposition on platinum surface

I was given a problem I have to solve, unfortunately I cant wrap my head about it. I've searched the page for answers but they doesnt seem to fulfill my needs, so i'm asking for little guidance. The ...
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1answer
39 views

what is the physical significance of ∆H=∆U for a chemical reaction?

In case of few chemical reactions $\Delta n=0$,so according to the equation $\Delta H= \Delta U+\Delta nRT$ change in enthalpy equals change in internal energy. But what does this in essence actually ...
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Is the total ionic-dipole bond (hydrogen bonds) acting on an ion stronger than the lattice energy holding the ions together?

When magnesium chloride dissolves in water, its $\Delta H^⦵_\mathrm{sol}$ is negative. Since $\Delta H^⦵_\mathrm{sol} = \Delta H^⦵_\mathrm{hyd} - \Delta H^⦵_\mathrm{latt},$ this means $-\Delta H^⦵_\...
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How to find relative lowering of vapour pressure from phase diagrams in terms of temperature?

Problem Answer My question Does a tie rule exist for solution solvent phase diagram to express relative lowering of vapour pressure in terms of temperature? The phase diagram is the one ...
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Why was Avogadro's number chosen to be the value that it is? [closed]

I understand that the mole is an extremely useful way of measuring and understanding atomic quantities. However, I can not find anywhere on the web why is it, that Avogadro's number was chosen as $6....
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Why does changing the pressure not affect the yield of hydrogen at equilibrium? [closed]

I have an equation for a reaction to produce hydrogen: $$\ce{CO_{(g)} + H2O_{(g)} <=> CO2_{(g)} + H2_{(g)}}$$ Could you help me to understand why changing the pressure does not affect the ...
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What does the value of the pH meter mean when there aren't any hydronium ions in the substance being tested? [closed]

What does the value of the pH meter mean when there aren't any hydronium ions in the substance being tested? How does the pH meter show a value which fluctuates as non-aqueous solvents are being ...
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49 views

The amount of heat energy required to raise the temperature of 1g of helium at NTP from T1 K to T2 K is?

The amount of heat energy required to raise the temperature of 1g of helium at NTP from $T_1 \pu{K}$ to $T_2 \pu{K}$ is? My confusion is, that as the gas is at NTP, therefore, it is an isochoric ...
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WHAT IS mole concept [closed]

i am finding stoiciometry tougher. i dont understand what is mole concept. How it is related to molar mass, atomic mass unit, gramper mole. Please explain
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From your graph determine the pKa value for this weak acid and report it in Blackboard to 2 decimal places [closed]

Use the data provided to graph the titration curve for 50 mL of a 0.4 M weak acid solution titrated with 0.45 M NaOH solution. From your graph determine the pKa value for this weak acid and report it ...
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Why reverse reaction is not possible in the case of dissociation of strong electrolytes and thus non existence of ionic equilibrium?

In chemistry textbooks there is generally written that ionic equilibrium can’t be achieved in the case of strong electrolytes (because their degree of dissociation is almost equal to 1) but it can be ...
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Is constant pressure heat capacity = entropy during adiabatic reversible expansion of perfect gas?

For any process, ∆G = ∆H - ∆(TS). Apply this on reversible adiabatic expansion of perfect gas, since the entropy of system does not change during this process, S is constant so ∆G = ∆H - S∆T The ...
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Specific conductance of KCl

Question: A conductivity cell containing distilled water has a resistance of $\pu{454 k \Omega},$ while the same cell containing $\ce{KCl}$ solution prepared in the same sample of water shows ...
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1answer
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How are molecular orbitals obtained in quantum chemistry?

When trying to solve for a molecule's molecular orbitals, we start off with the total molecular hamiltonian. However, given the difficulty of solving the Schrödinger Equation for this complicated ...
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1answer
32 views

Energy of the Orbital versus Energy of the Electron

When introducing the hydrogenic atomic orbitals, it is said that the 2s and 2p orbitals are degenerate. I have also read that for atoms with more than one electron, like He, the 2s and 2p are NOT ...
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Does direction matter in breaking a bond?

Im not sure if this question belongs here or in another community. I was wondering if the direction that we apply a force in order to break a bond matters and how it affects strength. Say we have one ...
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Calculation of Reynold number [closed]

Water stream (density 993.7 kg/m3, viscosity 0.656 mPas) is fed to the shell side of a shell and tube heat exchanger. The inner diameter of the shell is 45 cm, it contains 85 tubes of diameter 25/30 ...
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3answers
130 views

Is there any difference between getting dissolved and getting dissociated?

In the context of electrolytes only, is there any difference between electrolyte getting dissolved and electrolyte getting dissociated? According to my professor, they are different. He says a ...
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Boundary conditions in a closed system for diffusion (2nd Fick's law) in a porous medium

I would like to calculate the chloride redistribution in concrete (assumption: porous and homogeneous structure, purely diffusion-controlled mass transfer, closed system). For this I have derived a ...
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radical calculation with gaussian [closed]

I have neutral molecule (e.g. C2H2O) at ground state and I want to calculate its total energy with DFT method. I use Gaussian program. I wanna ask how it is possible to calculate it appearance ...
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1answer
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Open resource for spectroscopic raw data

Is anyone aware of reliable resources (ideally public) which allow the user to download the raw spectroscopic data such as infrared spectrum of small organic molecules, or rotational spectrum of HCl/...
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2answers
59 views

Antoine law and ideal gas law

I have the following question: A $100\ \mathrm{ml}$ sealed flask with $60\ \mathrm{ml}$ acetonitrile is heated to $140\ \mathrm{^\circ C}$. The boiling point of acetonitrile is $82\ \mathrm{^\circ ...
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1answer
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Seeing solubility in various cases

[![enter image description here][1]][1] Question is in the image 'match' each option having multiple answers. I have invested a considerable time over this but couldn't solve it. Anyone explaining how ...
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Interpreting phase diagram of mixture of partially-miscible liquid that boils before complete mixing

Source: Atkins' Physical Chemistry, 8th Edition, P.188 This is an example given by the stated reference book. Interpretations on this phase diagram is given. An extract of the interpretations is ...
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28 views

Different products using different indicators

A question states that 0.1 M solution of compound$$\ce{Na2CO3.NaHCO3.2H2O}$$ is titrated against 0.05M HCL, and that a different amount of HCL is used according to the indicators(phenolphthalein or ...
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Question on chemical equilibrium [closed]

8 moles of so2 and 4 moles of O2 are mixed in a closed vessel.the reaction proceeds at constant temperature. By the moment when equilibrium sets in,80% of the initial amount of so2 enters into the ...
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1answer
400 views

White hot hydrogen gas, like that during a big bang

Difficult to know for certain which field this is. According to what I can discover about it, the big bang explodes into being as white hot hydrogen gas, millions of degrees hot. I'm okay with that ...
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2answers
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How do you manage to liquefy a gas by applying only pressure? [closed]

How can you liquefy a gas by applying only pressure? To increase the pressure of a gas you need a compressor, and when the compressor does work on the gas , it will increase his pressure but at the ...
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3answers
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Colligative properties of colloids [closed]

The following lines are from my textbook: Colloidal particles being bigger aggregates, the number of particles in a colloidal solution is smaller than a true solution. Hence, the values of ...
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19 views

A question about potential difference across a membrane

Membrane potential of living cells arising from the difference of concentration of ions on both sides of the membrane, but why didn't someone use selective polymers as AEM (Anion Exchange Membrane) ...
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Symmetries and degeneracies of the s,p, and d orbitals

Consider the molecular AB_8 (complex with central atom A and 8 B ligands (coordination number 8), for which I determined the point group D_4d) and determine the symmetries and degeneracies of the s, p,...
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Grouping of symmetry classes in chemistry character tables

In the C3v point group, it lists three sigma Vs together in one column (class), and it doesn't list the cVs separately. Consequently there are three irreducible representations. In the C2v point ...
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5answers
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How can we define a non-spontaneous reaction?

Consider a reaction:$$\ce{$aA + bB$ <=> $cC + dD$}$$ The value of reaction quotient at a certain time $t$, $${Q_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}}$$ where the concentrations $[A], [B], [C]$ and ...
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2answers
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Concentration of gas above aqueous ammonia

I am a physicist who has run into some chemistry in the lab (and unfortunately, I've completely evaded any formal training in chemistry). I have exposed some samples (I think details of the sample are ...
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Effect of optical isomerism on colour of transition metal complexes

I know that different stereoisomers of a given transition metal complex (cis- and trans- forms) have different colours. But do different optical isomers (non-superimposable mirror images) have ...
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Relation between enthalpy, entropy and Gibbs energy at thermal equilibrium

$${\Delta S_{total} = \Delta S_{sys} + \Delta S_{surr}}$$ ... Equation (i) If system is in thermal equilibrium with the surrounding i.e. ${T_{sys} = T_{surr} = T}$ Increase/ decrease in enthalpy of ...
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Comparison of acidity of aqueous solutions of Lewis Acids

What can be the order of acidity of aqueous solutions of following Lewis acids: $\ce{FeCl3, AlCl3, BeCl2, NiCl2}$ The simplified reactions are: $\ce{FeCl3}$: $\ce{FeCl3 + 6H2O -> [Fe(H2O)6]^3+(...
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1answer
57 views

How to deal with the unit “Coulomb per equivalent”? [duplicate]

In a question that I came across they defined $1\,\pu{F}$ as 96500 coulomb per equivalent. Now as far as my knowledge is concerned $1\,\pu{F} = 96500\,\pu{C/mol}$. The question involved asks to ...
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24 views

Combining enthalpies of formation and combustion in the context of Hess's law

I know that you can use enthalpy of combustion to work out formation, and Formation to work out enthalpy change. But can you use enthalpy of formation and combustion data is the same Hess's cycle to ...
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2answers
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Why is the ionic product of water $K_w$ the same in acid, water, and alkali?

Seen on the web: The concentration of [H+] and [OH−] both vary based on the the composition (acid/alkaline) of the solution, but the remarkable thing is that their product does not. When [H+] goes ...
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1answer
85 views

Why is the carbon monoxide triple bond stronger than the nitrogen-nitrogen triple bond?

The $CO$ triple bond has a bond enthalpy of 1072 kJ/mol while the $N_2$ triple bond has a bond enthalpy of 945 kJ/mol, at least according to my source. The molecules are isoelectronic, so I couldn't ...
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5answers
2k views

What exactly is temperature?

I've read at many places that temperature is the average kinetic energy of particles present in an object. I just don't intuitively get how kinetic energy is connected with temperature. And how is ...
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1answer
25 views

How can I calculate Kp given Gibb's free energy? [closed]

I need to solve a problem but I can't seem to figure out how to move from the given values to Kp. Here's the question: 2SO2(g) + O2(g) ⇌ 2SO3(g) ΔrH° = −200 kJ.mol-1 and ΔrS° = −187 J.mol-1.K-1 at ...
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17 views

What is the lattice enthalpy of zinc chloride?

I am trying to find a literature value for the enthalpy of solution of zinc chloride to compare with my experimental value but I can't seem to find it. So I'm trying to use the formula: enthalpy of ...
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0answers
28 views

Network covalent bonds during melting

What happens to the intramolecular bonds when a network covalent substance is melted? I understand that in covalent molecular substances, the intermolecular bonds weaken between the molecules once ...

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