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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645 views

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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1answer
474 views

How many critical points? Why?

Critical points are defined (by wikipedia) as the "end-point of the phase equilibrium curve". I would say this diagram therefore has three critical points. But this is unnatural. I doubt its true. ...
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Estimating the protein concentration of an unpure protein solution

I'm confused on this problem for estimating protein concentration. Upon first glance, it looks like a simple Beer's law problem. but then there's the issue that the protein is not pure. How do I ...
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Given the Pair Correlation Functions for a Multi-component Fluid, is There a Simple way to Obtain the Helmholtz Free Energy?

I think it may not be possible. Given all the pair correlation functions, it seems possible to obtain the internal energy (assuming different species interact through pair-potentials (i.e. ...
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1answer
78 views

How to detect H₂SO₄ (aq) and NH₃

We have two bottle named $\ce{H2SO4~(aq)}$ and solution of $\ce{NH3}$ but we don't know their name actually. What I have to do to detect these solution by only using : $\ce{CuCl2}$ or $\...
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Why was anhydrous magnesium carbonate “upsalite” discovered so late?

What complicated the synthesis of upsalite (anhydrous $\ce{MgCO3}$), for it to be synthesized and published in 2013 as opposed to the 20th century, as one would expect for such a simple salt?
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What are the triple point pressure and temperature for pure cyclohexane?

Here is a video that demonstrates the interesting nature of the triple point of cyclohexane, so I tried researching on the internet for a phase diagram, but only found data from a manufacture where ...
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Why is snow white?

I know that this is a rather ambiguous question; but my question is, whenever we take water and freeze it in the freezer, it still tends to stay clear. Since snow is just frozen water, why is it white?...
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1answer
567 views

Understanding dissolution of CO₂ in Selexol and Rectisol

I'm trying to understand pre-combusiton carbon capture processes as described in this presentation. I'm told that solvents such as chilled methanol ($\ce{CH3OH}$) and dimethyl ethers of ...
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1answer
11k views

Finding molar mass of an unknown acid

"In the titration of a solid acid, an endpoint is reached after 22.0mL of 0.120 M $\ce{NaOH}$ has been added. Assuming that each acid particle contains two acidic hydrogens and both are ...
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Do liquid O₂ and N₂ form ideal solutions?

I suspect they do, but could not find data on this. (I mean at temperatures near those used in the distillation of liquid air.)
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Which is more: dissociated ions in water or undissociated? [closed]

While studying equilibrium we get to know that there are $1*10^{-7} \ce{~~OH-}$ and $\ce{H+}$ ions in pure water. However, I think there are more undissociated molecules.
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Dissociation of water into H+ and OH-: Does the law of mass action hold at nanoscale?

Suppose water under neutral conditions is confined in a virtual spherical nanocontainer with a radius of 25 nm. To calculate the number of hydronium ions, one uses water dissociation constant which is ...
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What stopper will stop HCl fumes?

The local hardware stores actually sell chemicals in recycled beer bottles with plastic stoppers as lids. The bottle of hydrochloric acid I bought is clearly losing gas to diffusion through the ...
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6k views

How to prove that entropy is a state function?

Consider the following steps: \begin{align} \mathrm{d}U &= \mathrm{d}q - p\,\mathrm{d}V\\ \mathrm{d}U &= C_V\,\mathrm{d}T\tag1\\ \end{align} Side question: Is equation $(1)$ only true for a ...
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How to calculate the Gibbs free energy from the equilibrium constant for the decomposition of sodium bicarbonate?

Solid $\ce{NaHCO3}$ is heated to $90~^\circ\mathrm{C}$. At equilibrium the total pressure of the gases produced is $0.545~\mathrm{atm}$. Calculate $\Delta G^\circ$ at $90~^\circ\mathrm{C}$ for the ...
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Is the atom the smallest particle, which takes part in chemical reactions?

According to modern atomic theory, the atom is the smallest particle which can take part in a chemical reaction. But during the formation of hydronium ion, $\ce{H+}$ ion reacts with $\ce{H2O}$ to form ...
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2answers
5k views

How do I determine if a process is reversible without numeric information?

How do I determine if a process is reversible without numeric information? It would be nice to know how to determine whether a process is reversible in order to solve problems LIKE this one: A ...
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Weighted Drilling Fluid Comparison with CaCl₂

I asked a question previously, and the answer was quite illuminating. The answer ushered me forth in a direction that finally made sense. I ended up finding this website, chem.latech.edu/~ramu/cmen522/...
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What is the actual reason behind PCl₅ existing as an ionic solid?

Why does $\ce{PCl_5}$ exists in the solid state as $\ce{[PCl_6]^{-}[PCl_4]^{+}}$? What is the problem with it that it doesn't exist in its original form in solid state? Like why isn't it just $\ce{...
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2answers
125 views

Any popular experiment in chemistry that digital signal processing played a crucial role in?

Is there any famous experiment in chemistry where digital signal processing played an important part? I don't mean using a machine that relies on such techniques (they all do) but an experiment where ...
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1k views

Where did all the elements come from? [duplicate]

I heard somewhere (I think is was a show called "How The Universe Works") that the big bang was the result of a hydrogen atom and a helium atom. Is this true? If so, where did all the other elements ...
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How do things heat one another? [duplicate]

For example, how does a gas stove heat a metal pot? A combustion reaction between the gas and the air takes place, and this releases energy due to new chemical bonds being formed. Do the atoms in ...
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14k views

Which formula is correct for calculating the heat of dissolution?

I want to calculate the energy change when a solute is dissolved in water. I know that I can achieve this by using the equation $q=mc \Delta T$. My question is does the mass ($m$) change with the ...
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Why is the volume in this compress gas cylinder constant throughout?

I am stuck on this gas question and its really stressing me out. A compressed cylinder of gas contains $2.25 \cdot 10^3~\mathrm{g}$ of $\ce{N2}$ gas at a pressure of $4.25 \cdot 10^7~\mathrm{Pa}$...
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1answer
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How can I calculate molality from molarity?

How can we determine the boiling point of 1 molar aqueous solution (density 1.06 g per ml) of KBr? If I use the colligative property formula than I require molality instead of molarity. Here the ...
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164 views

Entropy - Negligible?

In electrochemistry, the Nernst equation tells us the cell potential for non-standard conditions. I read that the factor $\frac{-RT}{nF}\ln{Q}$ accounts for difference in cell potential due to ...
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Rate constant and Michaelis Menten

Please consider the following figure of a concentration over time (msec) diagram with variables for an enzyme, a substrate bound enzyme and a product. Recall that $\ce{E + S \leftrightharpoons ES \...
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1answer
72 views

What happens to energy changes in non-reversible processes?

Take internal energy for example: $$dU\leq TdS-PdV$$ Firstly, I would like to make clear that the following question/argument relies on the following statement being correct: the left hand side of the ...
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1answer
3k views

Is there a difference between Joule coefficient and Joule-Thomson coefficient?

Is there a difference between the Joule coefficient and the Joule-Thomson coefficient? Also, I am having a hard time understanding what they mean.
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1answer
53 views

Oxide surfaces develop a charge in H2O. Do we have any, even vague, handle on how long does an indivdual charge last on avg. before being neutralised?

We often know, from e.g. titration experiments, what the average surface charge density of a surface is. How do these charges vary over both time and space (i.e. dynamics)? I have been unable to find ...
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Can an emulsion be emulsified?

Can clusters of an emulsion be emulsified into another emulsion? If so is there any common product or natural substance that would have such a structure? Finally is there a name for this? I looked ...
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Why are potentials of cells with magnesium electrode always lower than expected?

I have prepared the 1M water solution of magnesium acetate. Then I placed $\ce{Mg}$ and $\ce{Cu}$ electrodes in it. I predict there such reactions take place: $$\ce{Mg-2e^- \rightarrow Mg^{2+}}$$ $$\...
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554 views

Reaction Kinetics and Stoichiometry — Mass conservation

This question has been bothering me for some time, and I can't seem to find a good answer online. Say I have four chemical species $\ce{A}$, $\ce{B}$, $\ce{C}$, $\ce{D}$, and these four react in the ...
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153 views

Predicting rate equations from data

I am having trouble wit the following question on my problem sheet: "The reaction $\ce{Br- + ClO^- \to BrO^- + Cl^-}$ occurs with a rate constant of $\text{0.35 dm}^3 \text{mol}^{-1} \text{s}^{-1}$ ...
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Second order reaction half life equation?

For the reaction: $$2A\to p$$ The rate, $v$ may be given as: $$v=-\frac12\frac{d[A]}{dt}=k[A]^2$$ Correct? Integrating this gives: $$-\frac12\int_{[A]_0}^{[A]}\frac{d[A]}{[A]^2}=k\int_0^tdt$$ $$\...
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59 views

Would solar panels produce energy if uniform temperature in the universe? [closed]

If the temperature on the surface of the sun and on the surface on the earth were the same, and the temperature of the universe were uniform, would the solar panels produce energy?
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903 views

What is relationship between molecular weight distribution of PE and its strength?

I'm trying to figure out the relationship between the molecular weight distribution of a polyethylene plastic and its strength and heat sealability. (The molecular weight distribution is described ...
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140 views

Elastic scattering of x rays in 3D: the principle for XRD analysis

I have some trouble visualising scattering of x-rays in 3D, since all textbooks and examples present it in 2D. Under I will share some reflections (no pun intended) about the elastic scattering of x ...
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140 views

Quotable Literature for the Enthalpy of a Proton

A proton obviously has no electronic energy, no vibrational and no rotational degrees of freedom. Therefore I think it is fair to assume, that $$H(\ce{H+})=\frac32\cdot \mathcal{R}\cdot T$$ holds for ...
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How are nuclei stable?

We all know that the density of the nucleus is very high. Nuclei are made up of protons and neutrons, and while protons have the same charge, they are closely packed in a nucleus. How does the ...
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Can we do combustion caused by limited supply of air in a lab? How?

For example Ethyne in combustion by limited supply of air $$ \ce{ 2C2H2 + 3O2 ->[\Delta] 2CO2 + 2H2O + 2C } $$ vs. $$ \ce{ 2C2H2 + 5O2 -> 4CO2 + 2H2O + Energy } $$ What are the limits ...
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Electrical conductivity of graphite

On this Wikipedia page, the electrical conductivity of various materials are given in the third column ($\sigma \text{ (S/m) at 20}^\circ \text{C}$). I am interested in the entry for Carbon (graphite)...
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307 views

Is there a pressure dependent function for freezing points of water and carbon dioxide?

I'm trying to determine whether or not certain compounds form solid ice at certain atmospheric pressures. These pressures vary significantly, from 0.001 atm to 800 atm. I understand that there is no ...
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229 views

Is there any relationship between ultrasonication and temperature

In chemistry we use ultrasonication for cleaning vessels ,synthesis of chemical compounds (sonochemistry) etc.I know that during ultrasonication high temperature and pressure is formed "locally".But I ...
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1answer
173 views

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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Is it still possible for an amateur, a hobbyist, or a science buff to make relevant discoveries in chemistry today? [closed]

Consider astronomy. Hobbyists and amateurs are today still able to make small to moderate scientific contributions to their field. Is the same true in chemistry? I think there might be at least two ...
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Heat given off from an electrochemical cell compared to mixing reactants

My confusion regarding the difference between the heat given off in a reaction that takes place in an electrochemical cell compared to in a beaker/appropriate container when the reactants are simple ...
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Why does reduced mass help when talking about two body problems?

Firstly I would like to say that despite the fact that you may be thinking that this is a physics question and should probably be asked on that part of the website, I came across reduced mass for the ...
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Is atmospheric pressure acting only on the contents or also on the container?

$22~\mathrm{g}$ of dry ice is placed in an an empty $600~\mathrm{ml}$ closed vessel at $298~\mathrm{K}$. Find the final pressure inside the vessel, if all $\ce{CO2}$ gets evaporated? Now by applying $...

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