Questions tagged [physical-chemistry]
Study of macroscopic and microscopic phenomena in chemical systems in terms of physical laws and concepts [thermodynamics, statistical mechanics, kinetic theory, quantum mechanics...].
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General Doubt. My doubt about combustion
When we give flame to a newspaper it burns readily. What we need for a fire (fuel, heat, Oxygen) is also known as the fire triangle. But why does the paper not burn when we pour boiling water over it? ...
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Do we understand chemistry from particle physics?
My chemistry knowledge is of a high-school level. In high-school, the properties of atoms were mostly presented as empirical phenomena. We learned some physical principles such as the idea that ...
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Understanding the relationship between $\Delta G$ and $K_p$, $K_x$ and $K_c$
Upon reading the chapter about equilibrium from my physical chemistry book, I was convinced that
$$ΔG= -RT \text{ln}(K_p) \tag{1}$$
and that
$$K_p = K_x (P^{\sum v}) \tag{2}$$
where $K_p$ is the ...
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Why does Equilibrium shifts towards more dense phase while increasing pressure for phase change Equilibrium?
I recently read that when pressure of system in phase change equilibrium is increased, it shifts towards denser phase. So, in case of Melting of ice, increase in pressure results in shift towards ...
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Conflicts on spin directions in the molecular term symbol for O$_2$
We know that the ground-state electron configuration of O$_2$ is $K K (\sigma_g 2s)^2 (\sigma_u 2s)^2 (\sigma_g 2p_z)^2 (\pi_u 2p_x)^2 (\pi_u 2p_y)^2 (\pi_g 2p_x)^1 (\pi_g 2p_y)^1$. The spins of the ...
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A problem to find the the chemical potential from the free energy (Ginzburg-Landau/Cahn-Hillard)
I have a problem to derive exactly the spatial term of the chemical potential from the free energy of the Cahn-Hillard equation
So, let us start with the free energy of a binary mixture (A and B). The ...
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Help understanding osmotic pressure and van't Hoff equation
I am trying to understand how to interpret the van't Hoff equation for movement across a semi permeable membrane.
Let's say we have a concentration of 100 mM sucrose on the inside of a semi permeable ...
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Can a Transformer Last until the Heath Death of the Universe if Made with Inorganic Insulation? [closed]
Transformers have no moving parts in direct contact with other solids, do not rely on non-reversible chemical reactions, and do not rely on nuclear reactions. So, with inert materials, the atomic ...
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If I burn a log & contain all the matter, will the burned log weigh $E/c^2$ less than the unburned log, with $E$ being the energy from light & heat? [duplicate]
I understand that the change in weight would be tiny even to a physicist and nothing for any practical purpose. I am also not talking about smoke and water vapor. I am only referring to energy given ...
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Koopman's Theorem for Ionization energy and electron affinity
Why is Koopman's theorem a reliable approximation for ionization energy but unreliable for electron affinity? I understand that it has to do with cancellation of errors by orbital relaxation and ...
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Understanding $\mathrm dP_x$ in the derivation of Maxwell-Boltzmann distribution
In my physical chemistry book, it says:
In the study of molecular speeds, we must consider a range of speeds. If we don’t, the probability would be zero. This probability is proportional to the range ...
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Hydrogen under pressure and high temperatere released energy: what is this process? [closed]
I am given hydrogen that is put into some pressure and high temperature conditions. After this it was found out that mass has decreased. It was also found that energy was released.
Can someone, please,...
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Electrons and atoms
Electrons do not follow fixed orbits around an atom's nucleus but exist within "clouds of probability" (orbitals), where there is a high chance of finding them. As one extends the search for ...
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Why does the rotational level spacing increase when moment of inertia decrease?
In the rigid rotor approach we obtain the result that the spacing between different rotational energy levels in a particular vibrational state is $\nu = 2B(J+1)$ and $ B = \frac{ h }{ 8 \pi^2 Ic }$, ...
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Ground state bleach in transient absorption with at least 3 states
The ground state (GS) bleach (B) is usually described by "less absorption due to depletion of electrons in the ground state". See here.
But the bleaching should also occur when there are ...
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Can a homogeneous chemical solution really not be split by centrifuge?
Assuming I have a homogeneous solution such as salt in water. My intuition tells me that gravity or centrifugal forces would affect sodium ions more than water molecules. Theoretically, if I could ...
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Conservation of water?
I know that water can exist in various states (liquid, solid, ...) and can be in various places (clouds, oceans, ground, ...). What I want to know is whether or not the total number of water ...
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Phenomenon causing Voltage in Batteries
I have a simple question: you can think of a charged particle as a particle with mass, and hence there will be an electric field surrounding the charge, which causes electric potential energy (if ...
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Angular momentum uncertainty principle and the particle on a ring
By considering a particle on a ring, the eigenfunctions of $H$ are also eigenfunctions of $L_\text{z}$:
$$\psi(\phi) = \frac{1}{\sqrt{2\pi}}e^{im\phi}$$
with $m = 0,\pm 1,\pm 2,\cdots$. In polar ...
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Why cookies don't soak linearly in function of temperature?
I like to soak cookies in large coffee mug for breakfast. As a direct result of this, sometimes I try to soak the cookie in too quickly. The whole story is this:
When I try to soak the cookie in and ...
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Why is the mole an SI unit?
In the SI unit system you have stuff like mass and length which are pretty fundamental. But the mole seems to not be as fundamental as the others. I think we can express it in terms of the other ...
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Mass balance for gas in a fixed volume
I am trying to generate an equation that describes the mass balance of a gas in a fixed volume. The application is simulating the sweep out time of the cell in a laser-based instrument which measures ...
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Effect of impurities on boiling and freezing points
When impurities like salt is added to water, the boiling point of water increases because of what I think is vapour pressure, though I know very little about that too. However, with the same analogy, ...
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Nature of absorption spectra peaks similar profile in Dimethyl sulfide (C$_2$H$_6$S)
I was reading interesting article about possible life signs detection in exoplanets, where JWS telescope have captured that exoplanet K2-18 b atmosphere has Dimethyl sulfide traces. This chemical ...
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Circle-circle collision, linear and angular momenta transfer
I am trying to simulate particle collisions in two dimensions (hydrated ions). I have found the formulas I need for the transfer of linear momentum. However, I kind of suspect that angular momentum of ...
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Any method for measuring hydroxyl and hydroperoxyl radicals in water?
I am looking to irradiate water containing some amounts of iron and would like to measure the amount of hydroperoxyl and hydroxyl radicals produced in real time as a result of the irradiation. Is ...
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Why does cigarette smoke stay so stubbornly on our bodies? [closed]
How does anything stick to anything, for that matter?
Another example: why does perfume also stay so stubbornly on our bodies? And why do some perfumes stay longer than others on a fundamental level?
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Nonlinear correction term to Debye-Huckel equation for asymmetrical electrolytes
The Debye-Huckel equation for electrolytes in a solution is a differential equation for the potential function in the following form:
$$ \nabla^2\phi_j + \sum^{s}_{i=1}\frac{q z_i n^{(0)}_i}{\epsilon} ...
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The relation between state function and molecular orbitals
In some chemistry classes I was taught the (seemingly usual) 'tale of exactly two atoms' that form bonding and anti-bonding states in the LCAO-theory (similar to this question). I've not seen the ...
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Why does a mixture of bulk $\rm Hg$ + $\rm Cd$ +$\rm Te$ melt at a much lower melting point than any of its constituents?
In a real life setup, a mixture of $\rm Hg$, $\rm Cd$, and $\rm Te$ melts at approximately 330 degrees Celsius. The element with the lowest melting point is Te which melts at 449.5 degrees Celsius. ...
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Why does surface tension increase on addition of soluble impurities?
I read that addition of soluble impurities increase the surface tension of water. I initially thought it was because when soluble impurities dissolve in water it leads to the dissociation of that ...
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Refrigerated vacuum Soxhlet extraction
Say one wanted to efficiently extract a temperature sensitive and easily oxidized compound from a substance.
I envision a Soxhlet apparatus filled with a very low BP solvent like diethyl ether. Rather ...
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Why do hot water droplets persist in cooler water?
I notice this phenomenon typically when mixing hot or warm water with cold water. Basically, tiny droplets of hot water travel inside the body of cooler water and persist. I have included a photo of ...
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Regarding Degrees of Freedom and dynamics of polyatomic molecules [closed]
Justify how a molecule with N atoms have $3N-5$ vibrational degrees of freedom(Linear) and $3N-6$ vibrational degrees of freedom (Non-linear). Will this be valid for large number of N?
Taking $H_2O$ ...
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How many degrees of freedom does the water molecule have? [duplicate]
This is mainly a question about molar heat capacity. I've read many different values for the degrees of freedom of water, for example f = 12 on (https://en.wikipedia.org/wiki/Molar_heat_capacity).
But ...
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Patterns on melted, then solidified chocolate
Observation
I have melted some chocolate (in a bain-marie, or water-bath) in a bowl, and then turned off the stove. I let the hot and liquid chocolate stand there, letting it cool for a few hours at ...
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Thermodynamics and Gibbs energy
The equation for the Gibbs free energy is: $\Delta G = \Delta H - T\Delta S.$
$\Delta H$ is the amount of energy difference between the initial state (characterized by $U_{i}$, $S_{i}$, and $V_{i}$) ...
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Thermodynamics and entropy
In a thermodynamics process, when heat is exchanged ($\Delta H$), it causes a change of system from state 1 to state 2. As a result, the entropy of a system is changed irreversibly.
Can the change in ...
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Interpretation of non-spontaneous Gibbs free energy
Good day guys,
I was reading some books on physical thermodynamics, they explain that for system undergoing a chemical reaction whose $\Delta G < 0$ indicating that the reaction can then provide us ...
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Total energy of a rocket launch
I'm wondering how the total energy of a combined Earth-rocket system is conserved in a rocket launch?
Before launch, kinetic and gravitational potential energy of the rocket are 0. It then launches, ...
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How is energy conserved in formation of chemical bonds?
I understand that when an H$_2$O molecule is formed, it has lesser total energy than the constituent (2H and O) atoms. I also understand that the potential energy (PE) will be reduced when the atoms ...
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The equipartion theorem and degree of freedom in case of vibration
I have been taught in chemistry that,
the energy of a vibrational freedom is $RT$ (ie, twice that of rotational/translational)
The degree of freedom which I found in chemistry, for the vibrational ...
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Is it possible to use a water molecule's expansion/contraction effect with heat as a motor?
When water molecule is cooled, it is well known that it expands:
That's the reason the rocks in the desert explode in the cold of the night: the rocks have water inside that expands with cold and ...
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How do relativistic effects lead to gold not usually occuring in a 2+ oxidation state?
In the literature I found compounds where gold occurs in a 1+ and 3+ oxidation state, like the perovskite CsAuCl_3, and also came across the fact that gold usually doesn't occur in a Au2+ state. ...
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An egg gets soft before it gets hard [closed]
I found in a book from 1500's that says that when you cook an egg (I assume a raw egg), it will get softer before it gets harder. Is that accepted by the science community today? Can someone explain ...
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What melts faster at room temperature, frozen salt water or frozen fresh water? [duplicate]
Suppose you freeze 2 ice cubes in the same freezer at -6F. One cube is pure water, the other is a saltwater cube. Take both cubes out of the freezer at the same time and put them into a room at say ...
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Convolution or addition? Proper way to model overlapping absorption line profiles
Suppose you obtain a measured spectral line shape (let's call it 'envelope') which appears as a skewed/asymmetric voigt profile. You know physically that the envelope line profile has this skew ...
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Does fire cause friction in the fuel?
It is possible to create fire by friction. For example - by striking a stone with another stone or by striking a matchstick on a rough surface.
My question is: Can we say that, where there is fire ...
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Measurement of dipole electric field generated by a polar molecule
I'm trying to understand the nature of polar molecules. Have there been experiments where we can say to have actually measured the dipole electric field generated by a polar molecule such as hydrogen ...
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Enthalpy but why "add work back in"? Why internal energy $U$ was not enough? [closed]
The concept of Enthalpy has bugged me for quite some time. I just can't understand its meaning or reason for being.
Open|flow system enthalpy:
I think I fully understand why H is used in flow ...
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