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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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How do you figure out fuel specific impulse non-experimentally?

Simple question, probably very complicated answer: Without building a test engine/rocket and finding out experimentally, that is to say, based on chemical characteristics alone, how can one compute ...
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1answer
109 views

Why it the electron affinity of beryllium is greater than nitrogen? [closed]

As we know that fully filled electronic configuration is more stable than half filled electronic configuration, so in my opinion beryllium's electron affinity should be less than nitrogen's. Is my ...
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54 views

Effective attenuation coefficient for polychromatic light

The Beer-Lambert law gives the optical intensity of collimated light as a function of depth $z$ as: $$I(z)=I_{0}\mathrm e^{-\gamma z},$$ where $\gamma = \alpha + \beta$ is the wavelength-dependent ...
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1answer
47 views

Why are diagonal arrows disallowed in Jablonski diagrams? [closed]

My professor mentioned in one of our lectures that diagonal arrows in a Jablonski diagram are disallowed. As far as I know, horizontal arrows signify conservation of energy, while vertical arrows ...
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131 views

What about Miller Indices of planes passing through origin?

For Miller Indices of planes if we encounter a case where the plane passes through the origin then I have heard that the only remedy can be arrived by shifting the origin to a different point.However ...
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1answer
24 views

Calculation of rate law for multi step reaction [closed]

Please help me to solve this one. I'm having a bit of a hard time grasping these concepts.
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262 views

How is silver chloride more soluble in brine than water?

I heard that: Silver chloride is more soluble in very concentrated NaCl solution (brine) than in pure water. Is it true? I mean won't the common ion effect operate? Or may be this is due to some ...
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0answers
35 views

Seeming discrepancy between pKa and corresponding Ka of methylamine

The first entry in PubChem for the $\mathrm pK_\mathrm a$ of methylamine is $10.657$ at $25\ \mathrm{^\circ C}$. My elementary understanding is that this would be found as the negative log of the $K_\...
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63 views

Why are Txy diagrams curved for dew point and bubble point?

What is the reason behind drawing dew point curve and bubble point curve as curved (and dew point curved outwards and bubble point curved inwards) for Temperature vs Composition Phase Diagram as per ...
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109 views

Calculation of average bond length from force constant and IR absorption?

I need some help beginning a problem set problem (just want hints, I'd like to figure it out myself). The problem gives me the IR absorption for a diatomic, as well as the force constant for the ...
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214 views

Number of octahedral and tetrahedral voids present in a HCP structure

The given image depicts the tetrahedral and octahedral voids in HCP structure. For the tetrahedral part I figured out that there would be 6 tetrahedral voids in total. My visualisation: In the ...
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1answer
47 views

Why is the equilibrium constant unaffected by a change of the initial concentration?

In my class, it was taught that the equilibrium constant does not vary with the intial concentration of the reactants? Why is it so?
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114 views

What bonding allows chloroaluminate (AlCl4-) to form?

How is $\ce{AlCl4-}$ formed when $\ce{Al}$ only has $3$ electrons in it's outershell. It would be able to give $3$ electrons away with $\ce{AlCl3}$ for it to have a full outershell but how does it ...
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1answer
39 views

Solve for wavelength of photon given threshold frequency

The threshold frequency of a potassium metal plate is $\pu{4.35\times10^14 Hz}$. Determine the wavelength of a photon required to reach $\pu{2.50 eV}$ of the maximum kinetic energy of an emitted ...
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48 views

Comparing pressure and volumes of ideal and real gas

This question has been troubling me for quite a while now. Which has greater pressure: Real gas or an ideal gas under similar conditions? What about their volumes? I read this in many sources and ...
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2answers
74 views

Calculate Rate constant, k, for a consecutive reaction where k1<<k2

I have a consecutive reaction where the first step is the rate determining step so $k_1<<k_2$: $$\ce{A ->[$k_1$] B ->[$k_2$] C}$$ The rate law can be shown to be: $$[\ce{C}] = {1 - \exp(...
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2answers
66 views

Whether for all zero order reactions rate is independent of concentration of reactants

For example,for the reaction $\ce{A + B \longrightarrow C}$,If rate law expression is: $$\mathrm{Rate=k \times [A]^{(0.5)}\times [B]^{(-0.5)}}$$ It is a zero order reaction but whether it is ...
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1answer
119 views

Why do inert gas have zero electron affinity? [closed]

As we know, we have to apply large amount of energy to cause an inert atom lose electron, so in that case, shouldn't its electron affinity be negative?
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1answer
57 views

Expansion work by a gas when pressure is not explicitly constant?

How is it possible to calculate the work done by a gas when pressure is not explicitly stated to be constant? The question states: Calculate $\Delta H$, $Q$, and $W$ when $1\ \mathrm{mol}$ of He ...
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0answers
65 views

How to without calculations understand the liquid-liquid extraction efficiency?

I'm asking myself this question for a very long time and I haven't found a simple an good explanation yet for the fact that it's better (if you want to clean them) to wash your hands two times with ...
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1answer
66 views

Does a molecule need to be placed symmetrically in the unit cell?

I was watching an OCW by MIT (3.091X) on solid state. My previous notion of lattice point and unit cell got shattered after this example. Where are the unit cell and lattice points in this picture? ...
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1answer
565 views

Why do different gases have the same molar volume?

Molar volume: The molar volume, symbol $V_\mathrm m$ is the volume occupied by one mole of a substance (chemical element or chemical compound) at a given temperature and pressure. At S.T.P ...
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109 views

should charge balance be based on activities?

We have a fluid with $\pu{0.01 M}~\ce{HCl}$ and $\pu{0.02 M}~\ce{K2HPO4}$, so if we assume activity coefficients are $1$ throughout we can find pH as $6.800012$ and confirm that at that pH there is ...
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1answer
67 views

Maximum Concentration of Benzene possible

A question for my PhysOrg course states: Assume you are performing a reaction in which benzene is a reagent. What is the maximum concentration of benzene possible? Hint: what facts do you need to ...
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1answer
108 views

Why do the 4f and 5d orbitals have similar energies?

I've come to know this phenomena when learning about the exceptions to the aufbau principle. But there is no explanation of why 4f and 5d have similar energies (as I've read in some websites).
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PCl3 vs SCl2 boiling point

Why does sulfur dichloride have a lower boiling point than phosphorus trichloride? Is it to do with the higher number of electrons causing stronger id-id interactions in PCl3, or do we need to compare ...
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1answer
78 views

How many equal Xe–O bond length are present in (XeO_6)-3? [closed]

I tried to solve this problem by drawing a structure but the structure did not give me any answer and I was not able to draw the proper structure please help me out.
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1answer
42 views

Rate of a reaction [duplicate]

We know that the rate of a reaction $\ce{aA + bB -> cC + dD}$, the rate of the forward reaction is given by $r_\mathrm f = k_\mathrm f[\ce A]^p[\ce B]^q$ where $ a\neq p$ and $ b\neq q$ according ...
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1answer
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Molarity of a substance in a solution when more fraction is given

Mole fraction of ethanol in a solution with water is $0.040$. What will be the molarity of ethanol in water? Density of water can be assumed to be $1\ \mathrm{g/mL}$. This is how I tackled the ...
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1answer
93 views

How are the LCAO ansatz and Slater determinant ansatz for the wavefunction connected?

Say we have a system of 2 electrons, an ansatz for the wavefunction is then a Slater determinant consisting of two orbitals. $$ \left|\Psi_{Slater}\right>= \frac{1}{\sqrt{2!}}\left(\left|\phi_1\...
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3answers
242 views

What is Nesbet's theorem?

In a talk by Frank Neese there was a slide with title "Nesbet's theorem" and an equation indicating something like "if your wavefunction has the double excitation amplitudes correct, then you can get ...
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2answers
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Can there be any substance whose number of electrons and protons are different at neutral state

I want to ask that if there any substance that has the different number of electrons and protons at its neutral state
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1answer
33 views

States of matter.Liquid

In a book a read that a simple defination of liquid i.e."it is a material that assumes the shape of a container without filling it completely" but i cannot able to understand "without filling it ...
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1answer
123 views

What is 'power law' kinetics?

I've come across a lot of instances where 'power law' description of the kinetics was mentioned, but I cannot think of any integrated rate law that follows something like: $$A(t)=bt^n+c$$ I'm pretty ...
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1answer
74 views

How do we know that we have isolated a substance?

In The Historical Background of Chemistry by Henry M. Leicester page 131, the author says: Carl Wilhelm Scheele (1742-1786) [...] isolated many organic compounds, including hydrogen cyanide, lactic,...
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3answers
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Equilibrium for very small amounts of reactants

Is there any difference in the concept of equilibrium when it comes down to dealing with extremely small amounts of reactants? Say we have $$\ce{A + B <=> C + D}$$ and $K_c$ is $100,000$. If ...
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How does the equilibrium shift when concentration of reactant and product are increased simulatenously

Before answering my question, take a look at this example $$\ce{2NOCl <=> 2NO + Cl2}$$ Let's suppose I have 2 mol/l $\ce{NOCl}$, 2 mol/l $\ce{NO}$, and 1 mol/l $\ce{Cl2}$ in a closed system. ...
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1answer
130 views

Why do electrons in sigma bonds have zero orbital angular momentum about the internuclear axis?

As per the title, why do electrons in σ-bonds have zero orbital angular momentum about the internuclear axis? As far as I know, the outermost electrons participate in bonding. Suppose that the 3p ...
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1answer
56 views

Understanding energy level splitting of an octahedral complex from spin-orbit coupling, 1st and 2nd order zeeman effects [closed]

While studying notes from a couple years ago, I encountered a diagram that I don't have further information on but would like to understand. While I believe I managed to find sources to guide me ...
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1answer
124 views

Excluded Volume in van Der Waals equation

I was just reading over the EOS topic when where I stumbled upon excluded volume. Although the pictorial representation of the hard sphere model clearly shows that the excluded volume is 4 times the ...
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45 views

Is it necessary to write water as a reactant in the acid dissociation equilibrium?

If I wish to write out the acid dissociation equilibrium, is it necessary to write in the water as a reactant, or does it suffice to write the following? $$\ce{HA <=> H+ + A-}$$ Is it alright ...
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1answer
44 views

Reaction kinetics - Organic chemistry

On an exam in organic chemistry I was asked why the reaction B proceeds faster than reaction A. I answered that: in reaction B, I- is a better leaving group than Cl-, the reason being it is a weaker ...
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0answers
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Can oxidation peak tell anything about amount of gold deposited in cyclic voltammetry?

In doing an experiment which involved depositing gold nanoparticles by cyclic voltammetry, I was told the amount of gold that has been deposited can be estimated by comparing the size of the reduction ...
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1answer
125 views

Properties of azeotropes

Consider two liquids with vapour pressures in pure form being ${P^o}_A$ and ${P^o}_B$. ${P^o}_B >{P^o}_A$ which implies liquid B is more volatile. If the liquids formed an ideal solution, then a ...
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1answer
144 views

Balancing using oxidation number method

Balance the following equation using oxidation number method: $\ce{PbS + H2O2 -> PbSO4 + H2O}$ Attempt: I have written down the oxidation states of all atoms and we can observe reduction of ...
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2answers
320 views

Does the rate constant depend on pressure?

I have read in some books that when pressure increases, the number of effective collisions increases. Hence, $k$ depends on pressure. Is it true? If so, then why doesn't $k$ depends on concentration? ...
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Rotational barrier of biphenyl in ground and excited electronic states

I'm studying how the energy of biphenyl varies with its dihedral angle. I know how to describe the dependence quantitatively, but still, I don't know how to explain why the rotational barrier of ...
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Order of a complex reaction [duplicate]

Is the order of a complex reaction determined by the slowest step always? Is it so that order of a reaction is determined by rate determining step and since in a complex mechanism, we write elementary ...
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54 views

Oscillator strength of a transition

I am trying to compute the oscillator strength in a molecule. Therefore I've got its Energy level values plus both wave functions $\Psi_i$ and $\Psi_j$ for the transition I want to calculate the ...
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Where does hydrogen evolution occur when aluminium amalgam is placed in water - aluminium or mercury?

Let's say a drop mercury is placed on clean aluminium sheet; mercury amalgam is formed. The solubility of aluminium in mercury and vise versa at room temperature is fairly low. If the entire sheet is ...