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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Why does molar conductivity of a weak electrolyte exceed that of a strong electrolyte at low concentrations?
My textbook has this graph.
The only sort of explanation given is that conductivity increases on dilution because the salts ionise better. Which is incomplete because then the graph for KCl should be ...
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Could someone explain the ouzo/sambuca effect?
I know that ethanol is mixed with some ingredients as fennel which give to this its particular taste. Fennel and ethanol are mixed together. Ethanol is also mixed with water. The analogy is 60 percent ...
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Why is n=1 at a low pressure in the Freundlich Isotherm Equation?
On the topic of adsorption of a gas over a solid, the Freundlich isotherm explains this behaviour in an approximate manner via the following equation
$$ \frac{x}{m} = kP^{1/n} \tag{1} $$
where $x$ is ...
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Do complexes of a metal distribute in between the water and an organic compound layer?
My original question is one that is stated in the title, and I also have some side questions too.
I came across this question where you have a CuSO4 aqueous solution. Then you take an Ammonia aqueous ...
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Why would there be a non-zero Gibbs energy of mixing for ideal gases?
When two ideal gases $\ce{A}$ and $\ce{B}$ mix, they don't interact. The chemical potential of each gas is independent of the other, e.g. for $\ce{A}$:
$$\mu_\ce{A} = \mu_\ce{A}^\circ + R T \ln \frac{...
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How did Joseph Proust measure mass composition of NATURALLY occurring compounds?
note: I am not a chemist, I am just interested in this
Proust famously compared the mass composition by element of natural and artificially prepared copper carbonate and concluded they were the same, ...
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How to calculate pH of a 0.1 M solution of ammonium bicarbonate considering simultaneous equilibrium along with hydrolysis?
We need to calculate the $\ce{[H+]}$ of 0.1M $\ce{(NH4+)(HCO3^-)}$ given the $\ce{k_b(NH4OH), k_{a_1}(H2CO3), k_{a_2}(HCO3^-)}$
The hint tells me to directly use the result $\ce{[H+]=\sqrt{k_{a_1}(\...
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What is the basis for the relationship of Gibbs energy and extent of reaction shown in this graph?
How this graph of Gibbs free energy between reaction coordinate is made because because
∆G = ∆G° + RT ln Q
and since ∆G° and T is constant hence the graph should be like that of ln(x)?
Source: https:/...
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Calculating concentration quotient and determining direction of reaction for equilibrium involving gases
I'm currently working on a chemistry problem involving chemical equilibrium, and I'm having some trouble figuring out how to calculate the concentration quotient $Q$ and determine the direction in ...
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Validly of the equation, du= nCv dt, for an adiabatic process
In an adiabatic process, there is no heat exchange, hence, $Q=0$.
The equation $\mathrm dU=nC_V\,\mathrm dT$ is valid for every type of process given the gas is ideal, where $C_V$ is heat at constant ...
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Which way Le Chatelier's principle
I have been pondering about the effect of pressure change in regard to Le Chatelier's principle on reactions. For this, I considered the following reaction:
$$\ce{CO(g) + 3H2(g) <=> CH4(g) + H2O(...
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Is the activation energy for vaporization equal to the enthalpy of vaporization?
When ethanol, say, evaporates, the intermolecular forces between molecules need to be broken. As a vapour, there are no new forces being created, so it is a purely endothermic process, with no "...
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Does thorium(IV) oxide has a "fluorite" like structure? [closed]
The fluorite structure shows 8:4 coordination. Which of the following solutions has fluorite-like lattices?
$\ce{CaF2}$
$\ce{SrCl2}$
$\ce{BaF2}$
$\ce{ThO2}$?
My book tells me only $\ce{CaF2}$, $\ce{...
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Calculating the enthalpy of reaction at non-standard concentration for reactions in aqueous phase
Standard conditions for a chemical reaction in the aqueous phase, for instance, a chemical reaction in solution, consider that reagents should be at a 1 M concentration. I was wondering how to ...
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Ethylene Glycol in Wall Primer [closed]
No scientific background here!
Due to a chemical sensitivity, and general concern for healthier indoor air quality in a home I am renovating, I opted to choose "greener" alternatives in ...
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Can someone help me with the experimental tabulation or spread sheet data on enthalpy, temperature, and pressure for aluminum and oxygen combustion [closed]
I need an experimental tabulation or spread sheet data of enthalpy, temperature, and pressure tabulated in columns for aluminum and oxygen combustion under non standard conditions.
Any references to ...
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What causes HPLC peaks to look like gauss curves?
I was wondering how the form and curvature of HPLC peaks come to be. As I understand it, the mobile phase which contains the analyte, runs through the column. Many times, the distribution equilibrium ...
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Boiling of liquids and their vapour pressure [closed]
Hello I was wondering about the boiling of liquids, I will use water as an example.
Liquids boil when their vapor pressure function p(T) exceeds the ambient pressure, for example water boils at 100 °C ...
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∆G or ∆G° to predict spontaneity
I have a doubt about using Gibbs free energy to predict the spontaneity of a reaction.
It is shown that ∆G = ∆G° + RT ln (Q).
That said, in order to predict which direction the reaction spontaneously ...
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Enthalpy in an irreversible isobaric process
I know that in a reversible isobaric process, the enthalpy change of the system is the change in heat for that system. What happens if the process is not reversible? I.e only the outside pressure is ...
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Cp=Cv for isochoric processes?
According to the first law of thermodynamics, ∆U = ∆H + work done, where magnitude of work done is given by W = PdV.
In an isochoric process work done would be zero (provided the external pressure ...
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How is Clausius statement violated for reversible heat engines that are assumed to have different efficiencies?
I'm trying to verify that all reversible heat engines have equal efficiencies by using this diagram. Here, the second heat engine (HE2) is assumed to has higher efficiency than the first heat pump (...
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Effect of changing of the concentration of reactants when concentration of the initiator and the concentration of the initial reactant are very small
A + I---> p
What happens to the rate of the reaction when the concentration of the reactant is changed in a system that its concentration of its initiator and the concentration of the initial ...
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How can I find vapour properties of a compound molten salt?
I'm carrying out thermal-hydraulic simulations of the Aircraft Reactor Experiment (a nuclear molten salt reactor) based on circulating molten fuel salt: NaF 53 mol%, ZrF4 41 mol%, UF4 6 mol%.
While ...
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393
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Vacuum distillation of azeotropic mixtures
I was wondering if vacuum distillation can seperate azeotropic mixtures.
Consider the ethanol/water system. At 95.6% ethanol content, the system forms an azeotrope because the vapor composition ...
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Deriving reduction potential from redox reactions
From a past USNCO test:
40. What is the standard reduction potential of $\ce{Hg^2+(aq)}$ to $\ce{Hg(l)}$?
\begin{align}
\ce{2 Hg^2+(aq) + 2 e- &-> Hg2^2+(aq)} &\quad E^\circ &= \pu{+0....
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How can Joule-Thomson inversion coefficient of ideal gas be zero? Does temperature of ideal gas not change on adiabatic expansion?
Does Joule-Thomson coefficient being zero means there will be no change in temperature? If that is the case then according to first law of thermodynamics, E = Q+W (don't know how to add delta sign). ...
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Is it Rigorous to Derive the Arrhenius Exponential Term from the Boltzmann Distribution?
The Boltzmann distribution is a probability density function which expresses the probability of finding a particle in an energy state $\epsilon$ while in thermal equilibrium given a specific ...
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Explaining the low-lying electronic state of NO
The question asks the following:
'The molecule NO has a low-lying electronic state 0.015 eV above the ground electronic state. Explain why this is the case and state the electronic degeneracies of ...
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Chemical potential and condition for equilibrium in case of binary liquid reaction mixture
Suppose there is a liquid mixture with components A and B in equilibrium along with their vapours. Then with the Gibbs-Duhem equation we know that $$μ_A(\mathrm{liquid}) = μ_A(\mathrm{vapor})$$ and
$$...
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Why is the isenthalpic condition required in the Joule–Thomson effect?
I have been struggling to understand how the molecules behave during the Joule–Thomson effect. I would love to get some help on this concept. Here is what I got so far.
Under adiabatic and isenthalpic ...
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Work Done by the gas in Isothermal Condition against constant external pressure
Question :
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Under isothermal condition, a gas at 300 K expands from 0.1 L to 0.25L
against a constant external pressure of 2 bar . The work done by the
gas is( given that 1L.bar=100J)
Answer (from ...
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Does "brine rejection" happen for dissolved gases as well?
"Brine rejection" is the effect of sea ice pushing out dissolved salts, forming sweetwater ice and brine. I understand "freeze distillation", a method to concentrate alcohol in ...
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Concept of Absolute Thermodynamic Activity
In the textbook Electrochemical Systems by Newman and Alyea, Chapter 14: The definition of some thermodynamic functions, chemical potential of component (ionic or neutral) is written as a function of ...
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How do I find entropy change for surroundings?
I know how to calculate entropy change of the system but am not able to calculate entropy change for surroundings. The question is as follows:
Q: At $100°C$, water vapour at $1$ bar is in equilibrium ...
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Virial theorem confusion
Virial theorem says that $E_{t} = -\frac{E_{P}}{2}$ however this says that lets say for 2 gas molecules(Ne) the kinetic energy due to temperature a molecule of $Ne$ at 0K will have the same energy ...
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Why change of gibbs energy per mole is zero at equilibrium?
I was reviewing this concept and thought of this: $\frac{dG}{dt} = \frac{\partial G}{\partial \xi}\frac{d \xi}{d t}$, for a reaction to be at equilibrium $\frac{d G}{d t}$ must be zero but I have ...
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How to explain the acidity difference between these β-diketones?
In DMSO, pentane‐2,4‐dione (1) and 1,3‐diphenylpropane‐1,3‐dione (2) possess nearly identical $\mathrm{p}K_\mathrm{a},$ whereas 1‐phenylbutane‐1,3‐dione (3) is almost 1 $\mathrm{p}K_\mathrm{a}$ unit ...
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Acid dissociation of two polar liquids
I was thinking in a case where the solute and solvent are two different polar liquids and according to Does the acidity constant depend on the solvent? the constant of dissociation change with the ...
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Why are fluorine-19 NMR spectra less affected by paramagnetic centers than other common nuclei?
I know that 19F NMR spectra are less sensitive to paramagnetic centers as an empirical fact: it’s my experience and that’s what people in my lab have always been saying.
For instance, some of my ...
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Can anyone help me with the derivation for the formula of entropy?
I have this formula in the chapter of thermodynamics:
$$\Delta S = n C_v \ln\left(\frac{T_2}{T_1}\right) + n R \ln\left(\frac{V_2}{V_1}\right),$$
where $\Delta S$ is entropy, $n$ moles, $C_v$ molar ...
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Derivation of Flory's Model for Linear Condensation of Polymers
I'm having some trouble understanding a part of Flory's model for linear polycondensation reactions. In his 1936 paper, he derives an expression for the probability of the existence of a particular $x$...
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Does high pressure reverse reaction between zinc and sulfuric acid?
When zinc is added to sulfuric acid, it undergoes a chemical reaction that generates hydrogen gas and zinc sulfate. Can this reaction be reversed by applying pressure to the products converting them ...
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Experiment to crush soda can by air pressure
You put a can with water at its base on a hot plate and allow the water to heat. Once steam is visible from the opening on top of the can, you quickly flip the can upside down into a bowl of water ...
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Why is the boiling point of a iodoalkane greater than that of the corresponding fluoroalkane?
Why is the boiling point of ethyl iodide (b.p. 72 °C) higher than the boiling point of ethyl fluoride (b.p. −37 °C) even though the dipole–dipole interaction should be better in $\ce{C2H5F}?$ Is it ...
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Does a free radical localized at one atom in a compound make sense or could it be?
In most of our cases, a dot that represents a radical is always considered affiliated to an atom in a molecule, especially when we talk about a reaction mechanism.
However, Levine's Quantum Chemistry [...
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Potentiometric conundrum
I'm trying to develop a simple method of analysis based on the half-reaction:
$$\ce{Zn^2+(aq) + 2e- -> Zn(s)}$$
Making up the cell is a $\ce{Ag/AgCl}$ reference electrode. The cell is only $\pu{5 ...
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How does the electron get back to the ground state at the energy level? [closed]
I have a doubt about how this emission process is carried out in the atom where we have the orbiting electron and we want the electron to return to the fundamental value.
I know that in absorption we ...
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Contribution of vibrational degrees of freedom with different temperatures to internal energy
The vibrational degrees of freedom have a small contribution to the internal energy at normal and low temperatures, but this contribution will be important at high temperatures. Why is this ...
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Why can i not use glue (which contains cyklohexane, petrol and ethyl acetate) for gluing PVC materials? [closed]
The manufacturer do not recommend using glue to gluing PVC. But Why? Thank you for your help.
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