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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Is activation energy temperature-independent?
I know that activation energy for a reaction is the extra energy given to the reactants to reach the threshold energy so that they can collide and react. But then, why is it said that the activation ...
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How does association within vapor or dissociation within liquid affect the ideal nature of a binary solution?
As I understand, when there is positive deviation of a binary solution from Raoult's Law, the equilibrium partial pressure curve approach ideality (i.e a straight line dependence of equilibrium ...
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Knowing that CI is variational for any basis set, why is coupled-cluster variational in the full correlation limit?
This is the question asked in Martin's comment to my answer to: Why is Coupled Cluster not variational?
In the comment I was also asked to provide a publication as a reference:
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Pressure dependency in Haber Bosch ammonia synthesis
Haber-Bosch ammonia synthesis reaction:
$$\ce{3H2 +N2 -> 2NH3}$$
According to the ideal gas law: $pV=nRT$ where constant volume implies $\displaystyle \frac nV=\frac p{RT}$
Then $\displaystyle ...
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What is the correct discharge reaction in nickel-cadmium cell?
In school textbook
$$\ce{Cd +2Ni(OH)3->CdO + 2Ni(OH)2 + H2O}$$
Wikipedia
$$\ce{2NiO(OH) + Cd + 2H2O->2Ni(OH)2 + Cd(OH)2}$$
Chemwiki
$$\ce{Cd +NiO2 + 2H2O->Cd(OH)2 + 2Ni(OH)2}$$
Which ...
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Compare the work done during dissolution of carbides
1 mole of each $\ce{CaC2}$, $\ce{Mg2C3}$, $\ce{Al4C3}$ react with excess water in separate open flask. Work done during dissolution shows the order
$\ce{CaC2}=\ce{Mg2C3}<\ce{Al4C3}$
$\ce{CaC2}=\ce{...
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Why does the compound formed after a coordinate bond have a net charge? [closed]
Why does the molecule have net positive charge?
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Calculating excitation energies of a molecule
I am trying to calculate the excitation energies for the first three transitions of a molecule which is made up by a chain of k phenyl rings, where k shall be between 1 and 8. The angle between each ...
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Mismatch in the trends of atomic size and atomic radius
In the periodic table, the atomic radius decreases as we move from left to right in a period. However, the atomic volume should also decrease as a result of the decrease in atomic radius, as volume is ...
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Tunneling corrections in reaction rates
I've studied Transition State Theory since I asked this a while ago, but so far I have not been able to find a detailed explanation of how tunneling corrections are implemented into reaction rates ...
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Notation for excited states
I am reading some papers about quantum chemistry and in one I found a notation for excited states of a molecule that I don't understand at all.
In the picture below you can see the potential curves ...
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Calcium sulfate soluble in water
In the volumetric estimation of calcium in a given solution as calcium oxalate. We convert the calcium oxalate to oxalic acid by dissolving the former in hot (~70 °C) 2 N sulfuric acid solution. This ...
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Conductivity of Wüstite
"Wüstite is often represented as $\ce{Fe_{1-x}O}$, where $x$ is some small fraction less than unity. In this nonstoichiometric $\ce{Fe_{1-x}O}$ material
conduction is electronic and the material ...
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How to determine mobility when two mechanisms exist simultaneously
Two scattering mechanisms exist in a semiconductor. If only the first
mechanism is present, the mobility will be $\pu{250 cm2/V s}$. If only the
second mechanism is present, the mobility will be $\...
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How to find out which organic molecules would be good electron acceptors/donors on a GaAs semiconductor surface [closed]
I'm a physicist in way over my head.
I have a list of organic molecules to investigate, all common aldehydes and amines. My supervisor wishes to know which of these molecules would be good electron ...
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What is the relationship between emission and fluorescence?
A molecule exposed to a photon with some energy is put into an excited state, and emits a photon of some energy when it returns to ground state.
The photon that provided the energy for excitation ...
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When is phosphorus a polyatomic molecule?
Phosphorus is listed as a single element in the periodic table; however, I see that it is also a polyatomic molecule as $\ce{P4}$. I am trying to determine the number of atoms of phosphorus in an ...
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How to calculate n factor for O2 and H2 in this reaction? [closed]
How do I find n factor of $\ce{O2}$ and $\ce{H2}$ if I want to use equivalence principal on a reaction like $\ce{O_2 +2 H_2 -> 2 H2O}$?
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Ethane and ethene: which is easier to burn? Which one burns hotter? Why?
Anything that burns "easy", has a low activation energy ($E_\mathrm a$) for the burning process. Anything that burns hotter, will have a lesser enthalpy and thus, will have a more aggressive ...
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What happens to the methanol formed by the hydrolysis of methyl 2-hydroxybenzoate (oil of wintergreen) when synthesising salicylic acid?
Here are the reaction equations for reference (you may recognise this as a preliminary step for the synthesis of aspirin).
Steps for synthesis of salicylic acid:
1) methyl 2-hydroxybenzoate + sodium ...
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Is there a formula for density of any gaseous substance just based on its molar mass?
$\pu{112 ml}$ of hydrogen combines with $\pu{56 mL}$ of oxygen to form water. When $\pu{224 mL}$ of hydrogen is passed over heated cupric oxide, the cupric oxide loses $\pu{0.160 g}$ of its weight. ...
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What is the molecularity of the RDS of a zero order complex reaction?
If we have a zero order complex reaction (although uncommon in chemical practices), say the decomposition of ammonia:
$$\ce{2NH3 -> N2 + 3H2}$$
This is a zero order complex reaction. In my ...
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What is the relationship between the constant of equilibrium (Kc) and the position of equilibrium? [duplicate]
I understand that the constant of equilibrium is a ratio of the concentration of the products to the reactants and that this value allows one to estimate whether the position of equilibrium lies to ...
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Absence of anti-Stokes line in Raman spectrum
If we have a molecule 1H-25X which shows a band at $3000~\mathrm{cm}^{-1}$ in the IR spectrum and you want to record a Stokes and anti-Stokes Raman spectrum with a laser of 1000 nm, why is the anti-...
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When I heat up a balloon, does the air inside increase in pressure as well as volume?
When I heat up a balloon, does the air inside the balloon increase in pressure as well as volume? I thought pressure and volume were inversely proportional? Or does pressure and volume increase as ...
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How can we measure the rate of reaction of EDTA chelation with zinc carbonate?
I am performing an experiment in order to find the activation energy of EDTA chelation. Consequently, I need to measure the rate of reaction of the process. I am high school student, and so I do not ...
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How does the Lennard-Jones potential relate to energy?
Considering the Lennard-Jones potential,
$$V(r)=\frac{A}{r^{12}} − \frac{B}{r^{6}}$$
How does this relate to force or energy? I suspect that there is some physics equation I'm forgetting. I know ...
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What is the point of using molality when we have molarity?
Molality and molarity are both concentration terms. Given molarity's popularity molality seems rather antiquated. Why is molality still discused in modern chemistry classes?
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Finite probability from discrete distribution and zero probability from continuous distribution in Maxwell-Boltzmann statistics
I have difficulty understanding a certain concept with the derivation of the Maxwell-Boltzmann distribution $f(v)$ function from Boltzmann statistics. The derivation starts with the Boltzmann ...
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What is the pH of this H2SO4 solution? [duplicate]
I'm trying to solve a simple problem which is driving me crazy. It says:
Estimate the pH of a solution that contains 1 gram of $\ce{H_2SO_4}$ dissolved in 1 liter of water.
When I solve the ...
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Why do some chemical reactions require many steps? [duplicate]
I was a college student of physics ten years ago, and recently started to learn biochemistry. I enjoy finding out that some familiar concepts in physics play important roles in biochemistry such as ...
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Relative magnitudes of intermolecular forces from phase diagrams
Is it possible to say whether or not a system A or B has stronger intermolecular forces from a phase diagram according to which:
The $T_{\text{b}}$ of A is lower than the $T_{\text{b}}$ of B.
The $T_{...
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Ionization energy in Geiger counters
Geiger counters can detect radioactivity because nuclear radiation consists of particles or radiation of sufficiently high energy to eject electrons from atoms. Consequently, this type of radiation is ...
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Why do ions form condensation centres in isopropanol vapour?
In cloud chambers the particles are detected when a particle passes through the chamber causing the vapour to condense into a "cloud". What Process causes this observed phenomenon? In other words, how ...
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Do two Miller planes need to have similar arrangement of atoms?
For two Miller planes, do I need to have the same arrangement of atoms in both of them?
Does it need to look like the same plane translated a little?
I have this question because if this is not the ...
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Are acids and bases always aqueous? [closed]
I am tying to determine if an acid is a liquid or aqueous solution? Please can some one enlighten me?
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Why do some chemical reactions require many steps?
I posted the following question in Physics SE and was advised to transfer it to Chemistry SE.
I studied physics in college ten years ago and I recently started to learn biochemistry. I enjoy finding ...
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Is there a better model than the Kinetic Theory of Gases [closed]
I'm looking for a better relationship between the Kinetic energy of a gas and it's Temperature, and also how they vary with gravity (not altitude, just gravity!). So is there a model better than the ...
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Why does physisorption (physical adsorption) increase with ease of liquefaction?
This is what my textbook says about physisorption
The amount of gas adsorbed by a solid depends on the nature of gas. In general easily liquefiable gases (i.e. with higher critical temperature) ...
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How to use the calculate velocity correlation from VanHove correlation?
I am trying to derive an expression for the velocity correlation function $C(t) = \langle \mathbf{V}(t) \mathbf{V}(0)\rangle$ from the VanHove correlation:
$$
G(\mathbf{r},t) = \frac{1}{N}\left( \...
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Dependence of mass transfer coefficient on solubility
Does solubility of the solute affect the value of the mass transfer coefficient?
The book I am following mentions that the mass transfer coefficient is a characteristic of the constituent and its ...
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How do I calculate the enthalpy change when a gas is being used to heat water?
The question I'm trying to answer is:
Calculate the mass of butane gas that would be needed to heat $724\ \mathrm{cm^3}$ of water from an initial temperature of $7.44\ \mathrm{^\circ C}$ to $50.7\ \...
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If dG is a state function, why do reversible and irreversible paths differ?
For a reversible process at constant T,P in a closed system with no non-expansion work dG = 0. For an irreversible process under the same conditions, dG < 0. Since dG is a state function I would ...
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Predicting melting points of substances based on their molecular/atomic structure
Wouldn't it be great to be able to predict the melting point of a metal based on the atomic number and not by looking in some table for the value that was measured experimentally by someone else? Or ...
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What do 1T and 2H mean in front of compounds?
I have seen 1T and 2H used as prefixes for metallic compounds in literature, but I am having trouble finding what they mean. For example, 1T-HfS2 or 2H-HfS2.
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Why does the mole-fraction equilibrium constant depend on pressure and volume?
The ratio of rate constants for the forward and backward reactions gives us the equilibrium constant, $K_c$. For a sample reaction:
$$
\ce{A \underset{k_{-1}}{\overset{k_1}{<=>}} P + Q}\quad \...
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Dipole-quadrupole polarizability term for induced dipole
For describing an induced dipole, I have usually seen the following equation,
$$
P_{i} = \alpha_{ij}E_{j} + \frac{1}{2}\beta_{ijk}E_{j}E_{k}
$$
where $P_{i}$ is the $i^{\text{th}}$ component of the ...
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Find amount of benzoic acid in dissolution
Solubility of benzoic acid in water at $\pu{0^\circ C}$ is $\pu{1.7 g/L}$ and given the fact that $\pu{37 mL}$ was used to dissolve $\pu{1 g}$ of benzoic acid. How much of the benzoic acid would be ...
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Raoult's law & Dalton's law of partial pressures
I am confused between Raoult's law and Dalton's law of partial pressure as they state completely different things about same thing...
Raoult's law claims $p = P \cdot x$
where $p$ is the partial ...
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Calculating charge on amino acid from pKa
I have been given $\mathrm pK_\mathrm a$ values of an amino group, a carboxyl group and a side chain of cysteine. How can I find the ionic charge on it at different $\mathrm{pH}$ values?
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