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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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0answers
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Why can we know a materials properties by knowing its ground state at 0K - DFT

I have had this doubt ever since I was introduced to DFT. For what I gathered whatever results you obtained with DFT (by using VASP, quantum expresso or any other software) you can say those ...
8
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2answers
205 views

Calculating the strength of an ionic bond that contains poly-atomic ions

So the bond association enthalpy for ionic compounds like $\ce{NaCl}$ and $\ce{NaBr}$ can be easily calculated from a Born-Haber cycle. But the way a Born-Haber cycle is constructed it uses info that ...
5
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1answer
69 views

What happens to the first ionization potential when a hydrogen-like atom captures a particle?

This is a textbook problem from Resonance DLPD Physical Chemistry, Page #83: The mass of a proton is $1836$ times the mass of an electron. If a subatomic particle of mass $207$ times the mass of an ...
1
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1answer
54 views

Find the minimum temperature at which the reaction will become spontaneous [closed]

This question came in my entrance exam and I think 273 K should be the answer because the reaction is already spontaneous. I just want to know if I've attempted it correctly. For a certain ...
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1answer
43 views

Compressibility factor of hydrogen at low pressure and constant temperature

As we all know, the compressibility factor $Z$ of hydrogen and helium is always greater than $1$ at a constant moderate temperature. But, if we look at the virial equation of compressibility factor $$...
3
votes
1answer
45 views

Why is the ROHF spin density of the propenyl radical not symmetric?

I was preparing some material for my students and in order to illustrate the concept of spin density and how the ROHF method gives a purer description of this property than the UHF method. I prepared ...
0
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0answers
30 views

Theoretical Calculations for Potential Generated in Salt Water Battery

I am using a $\pu{1.5 M}~\ce{KCl}$ solution as electrolyte and copper and aluminium electrodes but no salt bridge. So basically there is only one beaker with the two electrodes in it with the $\pu{1.5 ...
0
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1answer
51 views

Melting Point of Pure Gold [closed]

The melting point of gold was changed from 1063 deg C to 1064 deg C in an ASTM procedure that uses the melting point of gold as the end point for a test. Did the melting point change somehow or was ...
0
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1answer
62 views

what the solution of this problem, negative absorbance values in UV-vis spectrum

In my project, I take the UV-visible spectrum of reaction between pyridinium chlorochromate and N-acetylcysteine. In some wavelengths, the absorbance value is negative for example it is (-0.006, -0....
6
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2answers
303 views

Why doesn't the particle in a ring model have a potential energy term?

I was thinking of the "particle on a ring" problem as a subdivision of a bigger problem, i.e. the hydrogen atom. While in the hydrogen atom problem, the Hamiltonian contains a potential energy term, ...
2
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2answers
227 views

Entropy change of isothermal irreversible expansion of ideal gas [duplicate]

Two mole of an ideal gas is subjected to isothermal expansion from $\pu{2 atm}$ to $\pu{1 atm}$ at $\pu{300 K}$. Calculate entropy change of the system, surrounding and total, if the process is ...
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0answers
35 views

Adiabatic flame temperature of a blast furnace gas

Calculate the adiabatic flame temperature of combustion of a blast furnace gas analyzing $25\%$ $\ce{CO}$, $10\%$ $\ce{CO2}$, and rest nitrogen. Use theoretical amount of preheated air at $\pu{1000 °C}...
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1answer
111 views

Which solution has higher boiling point?

Between a 2%(w/v) aqueous solution of NaCl and RbCl, which will have a higher boiling point. Here there are two competing factors. First there's the fact that NaCl has a higher concentration. So it's ...
1
vote
1answer
85 views

Determine surface area of heat exchange tube

A heat exchanger is used to cool down a stream of $\pu{20 kg s-1}$ of water from $\pu{80 °C}$ to $\pu{60 °C}$. The cooling water enters at a rate of $\pu{12 kg s-1}$ and $\ce{20 °C}$. The overall heat ...
0
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1answer
51 views

Why can't an electrochemical cell be a single cell? [duplicate]

If I put two electrodes of two different metals in 1 solution containing ions for both of the metals and connect these electrodes with a wire, do I still have an electrochemical cell ? Or does it have ...
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4answers
3k views

How could the ideal gas law be discovered from experiments on real gases?

The gas laws, namely Boyle's Law, Charles' Law, Avogadro's Law and Gay-Lussac's Law, are all experimental laws. Combining these laws, we get the ideal gas law $pV=nRT$. Also, "real life" gases do not ...
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0answers
21 views

3D printing of alumina

I want to print a structure of alumina, and the 3D printer that I am using is an extrusion-based printer. So I need your help in knowing that what composition (binders and deflocculant) of alumina ...
0
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1answer
25 views

How to apply the Principal of Atom Conservation (POAC) [closed]

27.6 g $\ce{K2CO3}$ was treated by a series of reagents so as to convert all of its carbon to $\ce{K2Zn3(Fe(CN)6)2}$. Calculate the weight of the product. I am asking here is that, why we are ...
3
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1answer
171 views

What does x mean in (1-x)A – xB composite materials, molar ratio, weight ratio or volume fraction?

I've been collecting data about ceramic materials and often I get to see composite materials are described as $(1-x)\ce{A} - x\ce{B}$. I am confused what this $x$ means. And I haven't seen any of the ...
2
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0answers
40 views

Existence of single ion activities

I have used Davies equation to find what I believed was single ion activities and multiplied them on concentrations to define the thermodynamic dissociation constants for any kind of buffer to find ...
2
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1answer
64 views

How to calculate the volume or mass of carbon dioxide gas absorbed by a calcium hydroxide solution?

Carbon dioxide reacts with calcium hydroxide as shown by the equation: $$\ce{Ca(OH)2 (aq) + CO2 (g) -> CaCO3 (s) + H2O (l)}$$ A solution containing $\pu{0.1 mol}$ of calcium hydroxide reacts ...
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2answers
74 views

Concept of enthalpy at a given temperature

In thermodynamics, we always quote a fixed temperature, whenever we mention enthalpy of a reaction. For instance, one can determine the enthalpy of combustion of methane at 25 °C. Now almost all ...
4
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1answer
683 views

I left a bottle of water in the fridge for the past three months. I took it out today. There was a block of ice in it. How?

How is this even possible? I know my fridge is not freezing items. The bottle was sitting at the back and I totally forgot about it. I went to empty it and heard a clank and noticed there was ice in ...
0
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1answer
62 views

How to determine if a mixing process is spontaneous at constant temperature but variable pressure

This is a conceptual question. Many times we work with the gibbs energy of mixing under conditions of constant temperature but not pressure. In a problem like this: Suppose that 2.0 mol H2 at 2.0 ...
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2answers
48 views

What happens when chemical equilibrium is restored after being disturbed?

I'm aware that, according to Le Chatelier's principle, a reaction will shift its equilibrium position in order to counteract the disturbance at equilibrium. However, I don't know what that means after ...
2
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1answer
63 views

Formulas for the number of spectral lines

While reading through Narendra Avasthi's Problems in Physical Chemistry, I came across two formulas on p. 64 (Scanned page): When electrons de-excite from higher energy level ($n_2$) to lower ...
0
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0answers
30 views

Using Maxwell–Boltzmann distribution in reacting systems

In the book Physical Chemistry, a Molecular Approach by Simon and McQuarrie, the have used the Maxwell–Boltzmann distribution for velocity of molecules to estimate the the rate constant of a reaction. ...
2
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1answer
32 views

Identifying orbital given electron probability density plot

Being a high-school student, I only have a qualitative understanding of the wave mechanical model of atom. Below are my inferences regarding the plot shown in the above picture: The concerned ...
2
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2answers
94 views

Hydrogen vs neon in terms of entropy

I know that both molecular size and complexity increase overall entropy, but between the two I'm not sure which increases it more. Would 1 mole of hydrogen have the greater entropy because it is two ...
2
votes
1answer
40 views

Volume of air required to oxidize glucose

In the body, the oxidation of glucose is according to the reaction: $$\ce{C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O}$$ Knowing that glucose consumption is $\pu{2.47 mol/d}$, What is the volume of ...
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2answers
41 views

Molarity and equilibrium reactions Kc [closed]

Samples of $\ce{A}$ ($\pu{1.40 mol}$) and $\ce{B}$ ($\pu{0.80 mol}$) are placed in a $\pu{2.0 L}$ container and the following reaction takes place: $$\ce{2 A (g) + B (g) <=> C (g) + D (g)}$...
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1answer
20 views

Combination of several unit symbols when finding new pressure from ideal gas law

As a car is driven, the tires heat up and the volume and the pressure change. Calculate the new pressure of a 35.0 L tire initially at 235 kPa that expands to 36.5 L when it heats up from 15.0 °C to ...
9
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1answer
155 views

Dominant contribution of v = 0 → v = 1 transition in vibrational spectroscopy

Recently I had studied vibrational spectroscopy using the quantum harmonic oscillator model. After stating the gross selection rule [that vibrational oscillation demands a change in dipole moment for ...
0
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1answer
50 views

Why doesn't chemical equilibrium lead to uncertainties?

Let's consider a reaction $$\ce{a A + b B <=> c C + d D}$$ We will also assume that the concentrations are low and the activity coefficient is one. Now let's say initially one has $p_0$, $q_0$,...
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109 views
+50

Boltzmann factor vs. graph of Maxwell–Boltzmann distribution

In discussions of the Arrhenius equation describing how rates change with temperature, there is often a reference to collision theory. In the Arrhenius equation, $$ k = A \exp\left(-\frac{E_\mathrm ...
2
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1answer
73 views

How are octet-rule models supported by thermodynamics and quantum theory? [closed]

I understand that the four quantum numbers dictate how many electrons can "fit in a shell," but I don't understand how gaining a full octet is particularly energetically favorable. The example of ...
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0answers
21 views

why does our milk split? [duplicate]

We have a bottle of milk that is half gone. It is not sour. If I pour hot water onto instant coffee, and then top up with this milk, the milk splits into a grainy solid. If I repeat the process but ...
2
votes
1answer
64 views

How to calculate the standard Gibbs energy at equilibrium?

Given that $K_c = 1.7 \times 10^{-13}$, calculate $\Delta G^{\circ}$ for this equilibrium mixture at $\pu{298 K}$. $$\ce{N2O (g) + \frac{1}{2}O2 (g) <=> 2 NO (g)}$$ I've calculated: $$ \...
0
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1answer
42 views

What is the difference between ΔfH and H-H° in NIST–JANAF tables?

Can someone explain the difference between $Δ_\mathrm{f}H$ and $H-H^\circ$ in NIST–JANAF tables?
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0answers
34 views

What's causing this dip in the FCS curve?

This is a fluorescence correlation spectroscopy measurement of light harvesting complexes. What could be causing the dip at 100 microseconds? Edit: The same thing was observed using fluorescence ...
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0answers
36 views

Can a substance be extracted from solution by adding another substance with a higher solubility?

Suppose that I have a substance X dissolved in water. I then add a substance Y to the solution. Substance Y has a higher solubility in water than substance X, and more than enough of substance Y is ...
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1answer
37 views

What would be a stable way to hold lithium hydride powder?

I currently have 100 grams of lithium hydride powder that needs to be held in a solid form. Initially, I was considering using cement, however, the moisture require converts the lithium hydride to ...
0
votes
3answers
42 views

What are the possible magnetic quantum numbers of silver? [closed]

What are all the possible quantum numbers ml and ms of the electrons in the outermost s orbital of silver? I'm new to this concept. Can anyone walk me through this?
0
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1answer
45 views

Work done by gas in isothermal process [closed]

A $20\ \mathrm l$ steel cylinder containing $\ce{N2(g)}$ at $20\ \mathrm{atm}$ and $300\ \mathrm K$ is kept in a big jar containing air at $1\ \mathrm{atm}$ and $300\ \mathrm K$ and sealed. $\ce{N2(g)}...
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1answer
34 views

Quantum Chemistry [closed]

How to find the degeneracy of a given state in quantum mechanics? What is the formula?
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2answers
101 views

What is the real pKa of water?

What is the $\text{p}K_\text{a}$ of water? A simple google search yields the value $15.74$, but this site and this paper say it's $14.0$. According to my understanding, the correct answer should be $...
2
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1answer
51 views

Impact of Pressure on equilibrium of Tin allotropes

The pressure at the bottom of the Mariana Trench in the Pacific Ocean is $1090$ bar. What temperature will the two allotropes of tin be at equilibrium? Assume that the molar volume, energy, and ...
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2answers
48 views

Finding percentage of the gas in a binary gaseous mixture of the given density

At STP, the density of a gas in a vessel is $0.9002$. If the gas is a mixture of argon and helium, what percentage of the gas is argon? I am stuck on this. From what I can gather, the only ...
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1answer
29 views

which one is the correct statement of “Law of definite proportion”? [closed]

according to my genius Teacher ' this law state that "the composition of a compound in terms of atoms (Not Mass) remains constant". His Proof: H2O and D2O are similar compounds (because H and D have ...
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1answer
20 views

Is the Gibbs energy of bulk metals in a Daniell cell affected by temperature? [closed]

From literature values, it is implied that the change in Gibbs energy of a Cu-Zn voltaic cell is largely due to the difference in Gibbs energy of the bulk metals (solid Cu and solid Zn). Does ...