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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Proof of Dynamic Nature of Equilibrium

Here is how my textbook proves that dissolution of solid in liquid is dynamic in nature. It considers the example of a saturated solution of sugar. It says that, Though the solution is in ...
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Determination of the integrated rate equation for a reaction

We were given this equation to determine its integrated rate equation: $$\ce {A + B <=>[$k_1$][$k_2$] C +D ->[$k_3$] E + F}$$ We were given these assumptions to simplify the derivation: $\...
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How is the Rate Law of a reaction measured?

What is Rate Law of the reaction below?$$\ce{4 HBr + O2 -> 2 H2O + 2 Br2}$$ How do we approach finding the rate law of reaction? Can this be found out only through experiments?
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Distinguish between two possible configurations for angular momentum in carbon atom

Consider the possible values of $S$ and $L$ for carbon configuration $1s^2 2s^2 2p^2$ and the corresponding rapresentations with arrows indicating the spins (consider only $S=0,L=0$ and $S=0,L=2$, as ...
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How to obtain spectroscopic constants Omega_e, Alpha_e, B_e, D_e and D_0 from centrifugal constants?

I need to compute a spectroscopic constants of $N_2^+$ states and I would like to do it using LEVEL16 software, due to its high interpolation flexibility. But it seems, that LEVEL16 can only compute ...
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Why does copper form bubbles in vinegar in this situation?

I watched this video in which the host tries to show the principles behind the voltaic pile. The host first immersed zinc in vinegar and bubbles are observed forming around zinc. I've learned that ...
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Gas phase chiral molecules

Are there any molecules that are chiral that are also gases at room temperature? Failing that, what chiral molecules have a high vapor pressure? Propylene oxide has a boiling point of only 34 C, so ...
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Observing bands which I shouldn't be!

I performed the iodine spectrum experiment to observe vibronic transitions. I heated the iodine crystals to produce vapors (at a little above room temperature) and observed absorption spectrum with a ...
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Why is so different the temperatures of a compressed gas compared to a liquid/gas mixture of the same fluid and they are both at the same pressure?

Why does $\ce{C3H6}$ gas when compressed (in a centrifugal compressor) comes out with a pressure of $\pu{16 bar}$ and $\pu{90 °C},$ and when it is a mixture of $\ce{C3H6}$ liquid/gas stored inside of ...
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Why are there distortions in electron cloud in molecules? How does increase surface area amplify these distortions?

In the physical properties of hydrocarbons,it is said that branched hydrocarbons have relatively less boiling point than it's linear form. From what I have learnt is that it is due to the increase in ...
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When fugacity and z-compressability equations instead of Gibbs free energy equations?

In very high pressure environments such as mud circulating systems, conditions for polymers contain fugacity/z-compressability criteria instead of Gibbs free energy, more in the answer. So When ...
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Using enthalpies of formation and combustion to find formation enthalpy of Acetylene (Hess' Law)

I understand this is a simple question (I’m in high school), but for some reason the numbers just are not working for me. Given: $$\Delta H^\circ_\text{c} = -1301\ \mathrm{kJ}\ \text{for}\ \ce{C2H2(...
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On the scale of stuff with a pH

I am a confused (and somewhat anal retentive) non-chemist who is trying to understand what pH is. I have come to understand it is a measure of acidity, but I have not yet figured out what that means ...
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173 views

Molpro - Connection between atomic term symbols and system symmetry

Let's say I have a carbon atom with the electron configuration $1s^22s^22p^2$. We know, that using atomic term symbols we can describe the following states: $${}^3P_0, {}^3P_1, {}^3P_2, {}^1D_2, {}^...
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Henry law and equilibrium

Is Henry's law a consequence of the equilibrium between a substance S in aqueous phase and the same substance S in gaseous phase? What I mean is, is it correct to treat Henry law as a manipulation of ...
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ph & pOH - Autoionization of Water

So I was learning about pH and pOH and it made sense. I looked at strong, weak acids & bases and learned that they dissociate completely in water. So then I moved on to water and learned about the ...
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Do only outer electron shells take part in forming chemical bonds?

Do only outer electron shells take part in forming chemical bonds? Or could an inner shell create a bond under some conditions?
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Aurora borealis - less favored energy transitions higher in atmosphere?

This question describes how some energy transitions become more prominent as you higher in the atmosphere. Short summary: Some electron transitions are "forbidden" by quantum mechanical selection ...
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Is it possible to boil a liquid by just mixing many immiscible liquids together?

In open air, when vapour pressure reaches 1 atm, boiling takes place. I read that if we add two immiscible liquids together, the total vapour pressure of the 'mixture' is close to $p = p^*_A + p^*_b$,...
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Estimating stability and mean life of anomalous tautomers

A pair of bases in the DNA, say, A-T, have a tautomerized form A*-T* (resulting from switching the sides of both protons along the hydrogen bridges). I have studied how, by means of DFT computations, ...
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How does absorption spectroscopy work?

So a beam of white-light photons passes through a gas and various photons, having exactly the same energy as the gas's molecular energy transition state deltas, get absorbed. We then get a ...
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Why is the melting point of tert-butyl alcohol 140 °C higher than that of sec-butyl alcohol?

This is one of the most drastic differences in a physical property I've ever seen for two such similar molecules, and in a simplistic sense anyway the difference lies in the opposite direction from ...
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In a molecular dynamics context, is the methyl rotation in propene a symmetric or asymmetric internal rotor?

In a prior question, I asked about the (a)symmetry of the potential energy surface of the methyl rotation of propene. In that context, the kinetic energy of the nuclear motions is of course assumed ...
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What is the underlying chemistry behind the triboelectric effect?

I remember briefly studying the triboelectric effect in Physics but as I now approach the domain of Chemistry, I'd like to know what processes are involved (at the molecular level) when the the ...
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A quick method for separating liquids?

I'm looking for a way to take 3 separate liquids (liquids which function as paint -- they will all be different colors), put them together into a container, and then rapidly separate them back to ...
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Vapor Pressure Paradox

This is quite an interesting situation I had thought of. Consider two beakers, each containing $\pu{180 g}$ of water. Also, suppose one of the two has $\pu{1.8 g}$ of glucose dissolved in it. Let's ...
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Why is the relative atomic mass of carbon not exactly 12?

Relative atomic masses of atoms of all chemical elements are numbers without units, being the value of proportion compared to $\frac{1}{12}^\text{th}$ the mass of the carbon atom. But the relative ...
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Does the methyl rotation in propene have a symmetric or asymmetric potential energy surface?

Depending on how one imagines the methyl rotation of propene to occur, it seems like it could exhibit either a symmetric or an asymmetric potential energy surface. If the $\ce{H2C=CH\! -}$ portion ...
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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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Why so few fluid phases?

Taking a look at the phase diagram of water By Cmglee - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=14939155 I see ice phases as much as up to 'Ice XI', but only one '...
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If the pH is zero, what would be the normality of a sulphuric acid solution?

If pH of the solution is zero, what would be the normality of $250 \, \mathrm{ml}$ $\ce{H2SO4}$ solution? My work: $\mathrm{pH} = 0$, hence the concentration of $\ce{H+}$ ions is $\pu{1 mol L^-1}$, ...
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Why do chlorinated silanes have lower boiling points than their methane analogs?

The boiling points of the chlorinated silanes and methanes are given below: $$\begin{array}{ccc} \hline \text{Species} & \text{Boiling point (X = Si) / }\mathrm{^\circ C} & \text{Boiling ...
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How to do Lowdin symmetric orthonormalisation?

Löwdin symmetric orthonormalisation seems to be a common practice in quantum chemistry. I come from a different background though and have to understand it and possibly implement in a computer code. ...
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Chemical bonding and dipole moment

We know that ammonia undergoes amine inversion. Why doesn't the dipole moment decrease in ammonia, since the direction of the dipole changes to the opposite direction every time there's inversion? ...
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Properties of steel and aluminum alloys

I have been trying to compare 304 stainless steel with 7075 aluminum for some personal research. This steel alloy has a specific heat capacity of 500 J/kg-C, while for aluminum the value is 960 J/kg-C....
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Free energy and kinetic energy for reacting gases

I am confused about the energies we are talking about when speaking in regards to the Maxwell Boltzmann Distribution and activation energies. Is there an relationship between kinetic energy and free ...
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Relation between the virial coefficients and van der Waals constants

I don't know where to begin with this question. A function $f(x)$ can be expressed as a special power series called the Taylor expansion. The common expansion is $(1-x)^{-1}=1+x+x^2$ Note that the ...
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What is reactivity really, and can it be quantified?

I understand the concept of a reactive species on a sort of vague and intuitive level: a reactive species is one that has lots of reactions that it can participate in. These tend to have large kinetic ...
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How is charge density a useful measure of polarising power and polarisability?

How do you use charge density ($Z/r$) as a measurement of polarising power and polarisability, and hence hard/soft acid character? So far I've been looking at different polarising power and ...
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Which is the strongest base?

When I was in lower grades, I was taught $\ce{NaOH and KOH}$ are the strongest bases. But I realised later that there can be more stronger ones. After a bit of research on the internet, I found these ...
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Master equation for catalyst and substrate binding?

I recently asked this on Biology.SE, and need to start with the master equation for the reaction: $$\ce{E + S -> ES}$$ Where $\ce{E}$ is our enzyme and $\ce{S}$ the substrate to get a probability ...
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Why is the standard enthalpy of formation of elements in their native forms zero?

Why is the standard enthalpy of formation of $\ce{O2}$ and other reference forms of elements equal to zero? Well, from what I know, bonding releases energy. Also, does anybody know a source for ...
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How can I measure the pH of high-viscosity fluids like dough?

I would like to measure the pH value of dough with a pH-Meter, to ensure a pH value of 4.1 (max). Because of the high viscosity I would thin down the dough with demineralized water for two reasons: I ...
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Law of Mass action VS Rate law [duplicate]

The Law of mass action has 2 parts - the equilibrium rate part & the reaction rate part. The "reaction rate part" states that rate of a reaction is directly proportional to the product of active ...
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Stability of ferrous ions and iron(II) hydroxide in acidic conditions

I was reading a chemisty textbook when I came across the following statement. $\ce{Fe(OH)2}$ is not stable, even more so in basic conditions. [---] $\ce{Fe^2+}$ ions are also less likely to oxidise ...
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How does the equipartition theorem apply to vibrational modes?

Specifically, how, based on the idea that energy will be shared equally among all degrees of freedom, does one come to the conclusion that each vibrational mode of a molecule will occupy $kT$ units of ...
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Effect of impurities on enthalpy of fusion of ice

When I freeze water with some impurities (1% NaCl by mass), the mixture seems to have a much lower enthalpy of fusion that pure water. The impurities cause the freezing point to depress to 0.6°C. I ...
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$K_{eq} $ vs $K_c$

I was wondering if there was a difference between $K_{eq}$ and $K_c$. I think they both refer to the Equilibrium Constant. If I'm wrong, could you please tell me the difference between the two? Thanks!...
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What chemicals help define “taste”?

As we all know that there are 5 tastes : sweet, sour, bitter, umami, salty. So what chemicals are there that help form these tastes, in other words how do our tastebuds experience these tastes? Also ...
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Why does the degree of dissociation change when we dilute a weak acid even though the equilibrium constant $K$ is constant?

$K$ represents the ratio of concentrations of molecules in a solution at equilibrium, which means that $Q_\mathrm{r}$ (that ratio at any given point) looks to be identical to $K$. In other words, the ...

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