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.
5,166 questions
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How does DMSO facilitate transdermal toxicity of sodium azide, and what are the key solubility, compatibility, and permeation kinetics involved? [closed]
Background
DMSO is a skin penetration enhancer. Sodium azide (NaN₃) is toxic. When mixed, DMSO can carry azide through skin without chemical change. I want to understand the hazards.
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What is the evaluation order of sign and unit in chemistry quantities?
I am curious about the evaluation order when a chemistry quantity has both sign and unit, such as $+3.4\,\text{kJ}/\text{mol}$.
Because there is space between number and unit, I think $e = (+3.4) \, (...
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What causes chemical shift difference in diasterotopic nuclei?
Specifically, I mean what physical phenomena contribute to the different shifts of diastereotopic nuclei and to what extent?
For example, in liquid-phase NMR, chemical shift is primarily determined by ...
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What does it mean to be more electron dense and also slightly positively charged?
I don't understand the following sentence from Wikipedia — Carbon monoxide:
The molecule is therefore asymmetric: oxygen is more electron dense than carbon and is also slightly positively charged ...
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What is the wavelength for first transition of conjugated molecules? (simplified particle in a box model)
The question is from Principles of Modern Chemistry 8e (Oxtoby), it is not that I couldn't find the answer, but rather that my answer doesn't match the textbook answers.
The question is of the form &...
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How to derive a particular expression for dU in a CSTR
Yesterday I created a thread asking about the underlying assumptions in energy balances of chemical reactors (example using a Continuous Stirred Tank Reactor operating at steady-state) and also what ...
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What assumptions underlie "thermodynamic" energy balances (example using CSTR) and what form does the balance take?
I am studying basic chemical reactors and it is often important to figure out, for example, how much heat we must supply or remove per unit time in order to keep our reaction going. In particular, ...
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Deriving mass flow rate from area and mass flux
I am trying to characterize mass flow rate for the two-phase flow through an injector. Given mass flux in a non-equilibrium two-phase flow and total cross sectional area of orifices, would it be ...
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Relationship between the Gibbs free energy and the equilibrium constant for heterogeneous reactions
According to my professor, the equilibrium constant can be determined as follows:
$$K_\mathrm{eq} = \exp\left(-\frac{\Delta G^\circ}{RT}\right)\tag{1}$$
My problem is that if liquids are present, then ...
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Liquids which can self-ionise
We know that water can self-ionise,
$$\ce{H2O <<=> H+ + OH-}$$
With the equilibrium constant at $298K$ given by
$$K_\mathrm{w} = [\ce{H+}] [\ce{OH-}] = 10^{-14}$$
I also came across the fact ...
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Why is thermodynamic equilibrium a reasonable assumption in tray-distillation columns?
I am studying the basics of binary tray-based distillation columns, and I have a general question. As I understand it, as the vapor flows up and the liquid flows down, at each tray, we assume that the ...
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Why does water oxidize preferentially over platinum at the anode in aqueous electrolysis?
In the electrolysis with $\pu{1 M}$ aqueous $\ce{CuSO4}$ and platinum electrodes, $\ce{Cu^2+}$ is reduced at the cathode and water is oxidized at the anode. But the standard oxidation potential of ...
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How is assuming standard hydrogen potential zero at all temperatures correct?
According to IUPAC — standard hydrogen electrode (SHE), the SHE potential by convention is taken to be 0 volts at all temperatures.
But once we assume that SHE potential is $\pu{0 V}$ at $\pu{298 K},$ ...
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Why do we not consider change in pressure in Gibbs free energy derivation?
My teacher taught me the $G = H - TS$ derivation in this method. But, in the fifth step (where we write $\mathrm{d}E+\mathrm{d}V = \mathrm{d}H$), isn't $H=E+PV$ and so $\mathrm{d}H=\mathrm{d}E+P\...
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Does equilibrium constant always stay independent of pressure?
It is often stated in books that the equilibrium constant $K$ does not depend on the pressure $p.$
But is that really true? Under high pressures (in GPa range) activities of species — even pure solids/...
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