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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2answers
426 views

Given this liquid-liquid phase diagram, is the green line the nitrobenzene-rich phase?

The temperature-composition diagram for hexane and nitrobenzene at 1atm. The region below the curve corresponds to the compositions and temperatures at which the liquids form two phases. The upper ...
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0answers
130 views

Have IH₃ and IH₅ already been synthesized?

I've seen a paper by Sikalov [1] that says that $\ce{IH3}$ and $\ce{IH5}$ should be observable. Has anyone actually tried to synthesize such molecules? References Sikalov, A. A. Hypervalent Halogen ...
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1answer
79 views

Work function and ionization energy

I've seen that the first ionization energy of a particular metal is always greater than its work function. This implies that the valence electrons in an isolated atom are more strongly bound than the ...
6
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0answers
58 views

Why is concentration used as a proxy for activity instead of mole fraction?

I am trying to understand how the Gibbs energy change of a chemical reaction is computed and I do not understand why concentrations (mol/L) are used as a proxy for activity rather than mole fractions (...
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1answer
123 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 ...
19
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2answers
473 views

Can molecules diffuse upstream when emptying a cup of tea?

I was drinking some tea, and I randomly decided to pour some into the toilet in an unbroken stream; can particles travel "upstream" quickly enough to reach the mug of tea? How fast can diffusion occur ...
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1answer
71 views

What in salt makes ice unable to refreeze? [closed]

I know that salt makes ice melt, but why does salt make the ice not refreeze? I have tried all different kinds of experiments, but I still cannot figure it out. The chloride acid in the salt makes ...
3
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2answers
82 views

On the angle subtended between the angular momentum vector and the applied field for a single spin

According to Dr James Keeler of Cambridge University in one of his lectures at Queensland University, the angle theta can be any angle, but I struggle to see how this is true. There are only a certain ...
4
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2answers
75 views

What repulsion keeps non-hydrogen atoms at a distance: between inner shells or between nuclei?

Bonded or not, when two atoms or ions come closer than the bond distance or the van der Waals distance, the energy increases drastically. What is the underlying cause of that repulsion? The repulsion ...
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1answer
31 views

Is there a name, or any specific jargon for a precipitation equilibrium involving a solid reactant?

Let's say you have some ions in solution, for example Na+(aq) and OH-(aq), and some partially dissolved solid, MgCO3(s), Mg+2(aq) and CO3-2(aq), which precipitates Mg(OH)2(s) until equilibrium. So ...
4
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1answer
272 views

How does radiocarbon dating work?

I'd like to better understand radiocarbon dating, however, I do not know what resources I must use in this regard. Could someone walk me through the process of radiocarbon dating with a few examples? (...
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19 views

On the origin of spin-lattice relaxation

According to P.J. Hore in the Oxford Chemistry Primer "Nuclear Magnetic Resonance" p57, 'the dipolar coupling, modulated by molecular motions, causes nuclear spins to experience time-dependent local ...
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1answer
2k views

Calculation of Atomic weight percentage in AAS

I am currently doing doping studies in a system similar to this ($\ce{A_{x}B_{1-x}}$) and I have to find atomic weight percentage of $\ce{B}$ element using atomic absorption spectroscopy(AAS). I have ...
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1answer
44 views

Does the prefix Ortho have some significance? [duplicate]

Are orthoboric acid and boric acid one and the same thing or we can not write H3BO3 as B(OH)3?
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3answers
86 views

Need help understanding Enthalpy

My chemistry textbook says that: Enthalpy (Internal Energy) = chemical potential energy + thermal energy Now, I know that Enthalpy and Internal Energy are different so I really don't understand ...
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0answers
18 views

How to find the molar concentration of two compounds mixed together in a buffer solution having the Kb and its Ph [duplicate]

Calculate how many milliliters of a $\pu{8.00 \times 10^{−1} M}$ solution of $\ce{NH3}$ and how many milliliters of a $\pu{7.80 \times 10^{−1} M}$ solution of $\ce{NH4Cl}$ are needed to get to a liter ...
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35 views

Effect of drinking on internal energy and entropy of the universe

I have just been doing some questions on thermodynamics and have come across a strange question that I can't seem to grasp. The question asks me to estimate the change in body temperature as well as ...
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1answer
22 views

How are cells rechargable?

I have learnt that you can test if a reaction is thermodynamically feasible by testing if the cell voltage $E_\mathrm{cell}$ is greater than $0$. Surely, if a reaction is feasible, then the $E_\mathrm{...
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10 views

Is Raoults Law valid if the solute is non volatile but have less vapour pressure than pure solvent?

We know that on adding a non-volatile solute to a pure solvent its vapour pressure increases because of the reluctance of solute to evaporate(i.e. strong intermolecular forces of attraction) Instead ...
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29 views

How to calculate the energy to dissociate a bond into neutral atoms?

I am self studying chemistry through MiT ocw 5.111 . On practice exam 2 problem 2 there is a question which states the following ...
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0answers
15 views

LIF spectrum with laser-coupled levels lines as the strongest

Why, if I excited the OH molecule Q-branch transition, my LIF spectrum (recorded during and after the laser pulse) does not result in only Q line being the most prominent, but also P and R lines with $...
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1answer
33 views

Surely distilled water is the answer to a polluted planet [closed]

I have been researching a long time on best water to drink and find that there are so many sources of pollution from industry, farming, agriculture and so forth creating run off into our fresh water ...
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2answers
1k 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. ...
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1answer
77 views

Entropy as a state function independent of the path

When entropy is a state function and the entropy change for a reversible process is $$\mathrm dS_\mathrm{rev} = \frac{\delta Q_\mathrm{rev}}{T} = 0,$$ how can an irreversible process be ...
11
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1answer
356 views

Oxidation of guanine with singlet oxygen

I'm studying the oxidation of guanine using singlet oxygen and one step of the reaction is not very clear to me. My problem is with the first step: it is a 4+2 Diels–Alder cycloaddition, and Fukui's ...
2
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5answers
136 views

Clarification on usage of dU =nCvdT

In many places I have come across the following derivation Work done in isothermal expansion By first law of thermodynamics $\mathrm dU=Q+W$ As $\mathrm dU=nC_V\,\mathrm dT$, and in ...
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1answer
34 views

Electrolysis of Baking Soda separated by semi permeable membrane

I have dissolved baking soda in battery water (de-ionized), in a glass beaker and used a food handling glove (vinyl) as a semi-permeable membrane to separate a graphite electrode from a copper ...
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0answers
19 views

Comparing rates of effusion between species

I'm struggling with (i) and (ii). I understand how to do (iii) and (iv) as it is just an application of Graham's Law of Effusion twice and n times (solve for n) respectively. I am starting with rate ...
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1answer
59 views

Effect of impurities on Enthalpy of vapourization

How does the Enthalpy of vapourization change when impurities are added? I know that the boiling point of a substance increases on addition of impurities, but how does the Enthalpy of vapourization ...
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0answers
45 views

Enthalpy of reaction between ammonia and oxygen

I have to ask this here because I asked literally everybody I know and I still disagree with them. Using the information in the table below, calculate the heat of released from the following ...
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1answer
141 views

Elevation in boiling point of water [closed]

$\pu{1060 g}$ of urea aqueous solution is subjected to heating. It starts boiling at $\pu{100.53 °C}.$ It is heated up to $\pu{102.12 °C}.$ Find amount of water vapourised in grams. (Pure water ...
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0answers
24 views

To calculate expansion work for a process

[1 mark] To calculate the expansion work for a process, 1) the formula $w = -P_\mathrm{ex}(V_2 - V_1)$ always works under all conditions. 2) the formula $\mathrm dw = -P_\mathrm{ex}\,\mathrm dV$ ...
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1answer
500 views

Molar heat capacity and heat capacity

Is molar heat capacity and heat capacity at constant volume both represented by $C_v$? at constant pressure both represented by $C_p$?
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2answers
53 views

Electron Ionization and the Franck-Condon Diagram: vibrationally excited and vibrationally ground states

I am currently studying Mass Spectrometry: A Textbook, third edition, by Jürgen H. Gross. On page 41, the author says the following: As explained by the Franck-Condon diagram, hardly any molecular ...
4
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2answers
172 views

Why is there a z² label for d orbitals, but no x² and y² labels with corresponding shapes?

I know that the $\mathrm{d}_{z^2}$ orbitals are named as a result from the conversion of the angular component of the hydrogen-like wave function in terms of Cartesian coordinates, but how come we ...
3
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0answers
46 views

Why does the electrical conductivity increase as the temperature decreases?

I am measuring the dependence of electrical conductivity of ( NaCl and $\ce{CH3COONa}$ solutions with concentration 9g/L) with temperature using conductivity meter. Theoretically the conductivity ...
3
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3answers
481 views

Can I express the rate of a reaction as percent per second (%/s)?

Rate is calculated as change in concentration over change in time, so usually $\pu{M/s}$ $(\pu{mol L-1 s-1}).$ Say, I'm calculating it for $20\%$ solution of ammonium hydroxide, so my final rate is ...
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1answer
40 views

What does it mean by “ concentrations are (value) in relation to each other”?

This is not a home work help question or something like that, these days I self learn chemistry and when I was doing a model paper I came across this question. And the question itself is not difficult ...
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1answer
27 views

Chemical Kinetics(Hypothetical elementary reaction) [closed]

For a hypothetical elementary reaction(image). Initially, only 2 moles of A are present. The total number of moles of A, B, and C at the end of 75% of the reaction is:
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2answers
7k views

Does the dipole moment increase or decrease by increasing the bond length?

It is established the dipole moment is a result of multiplication of the magnitude of charges (Q) and the distance between them (r). What I understand is that when an electron and a proton get closer (...
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3answers
240 views

How does the vacuum in atoms persist?

From very elementary chemistry I understand that atoms are mostly empty space, with a few tiny little objects whizzing around. There must then be a vacuum in between these particles. I always thought ...
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1answer
3k views

Why do we measure the initial rate of a reaction?

Why do scientists usually measure the initial rate of a reaction, instead of measuring the rate some time into the reaction?
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1answer
45 views

Why oxidation potential of an electrode equals negative reduction potential of the same electrode?

My textbook states that: $E^\circ_\mathrm{ox} = -E^\circ_\mathrm{red}$ (of same electrode) I know that electrons flow from anode half cell (oxidation) to cathode half cell (reduction). But if $E^\...
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1answer
52 views

Why is volume inversely proportional to pressure?

If temprature is directly proportional to volume (Charles's law) and temperature is directly proportional to pressure (Gay-Lussac's law), then why is pressure and volume are inversely proportional?
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0answers
16 views

Competing half reactions in electrolysis of aqueous solution of sodium hydroxide

If you run a direct current using pure nickel electrodes through a solution of NaOH in distilled water, you will separate the water into hydrogen and oxygen. Are there any other reactions that could ...
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0answers
30 views

Adiabatic compression of an ideal monatomic gas. What would the change in entropy be?

Two moles of an ideal monatomic gas initially at 300K and a pressure of 2 atm is compressed adiabatically using a constant external pressure $P_{ext}$ until equilibrium is reached. The temperature of ...
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0answers
50 views

Modifications and alterations in the state of chemical equilibrium

Let us consider that we have a mixture of gases, considered ideal, that is in balance. Like, for example, $$3\ce{NO} (g) \rightleftharpoons \ce{N2O} (g) + \ce{NO2}(g)$$ If we consult the ...
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2answers
48 views

Does the concentration of water accounts for determining the rate of a reaction?

I found this problem in my book and I'm not sure how to assess this question. It is as follows: Regarding the relationship between the rates of the chemical species in the following reaction. ...
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0answers
17 views

In UV photoelectron spectroscopy why are filled orbitals seen at a higher binding energy?

I understand that the partially filled Ni intersects the Fermi level as there is a change from filled to unfilled orbitals. But what is the explanation for the lower binding energy of the filled 3d Cu ...
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1answer
37 views

How do bonds form without violating the second law of thermodynamics [closed]

It might be obvious that entropy related to reactions always increases and I understand (somewhat) why this happens. My question is why if you have two hydrogen atoms in a vacuum without being bonded ...

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