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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9
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1answer
411 views

How to obtain product ratio from energy differences via Boltzmann statistics

I am currently calculating some reactions and I would like to express the ratio of the products in per cents. I am using the Boltzmann statistic in the following way: The probability $p_j$ of a ...
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1answer
327 views

How to find the potential of a mixed Iron/ Cer solution?

Given the following half-reactions: \begin{align} \ce{Ce^{4+} + e^{−} &-> Ce^{3+}} & E° &= 1.72~\mathrm{V}\\ \ce{Fe^{3+} + e^{−} &-> Fe^{2+}} & E° &= 0.771~\...
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2answers
1k views

Find the color of the solution

The acid-base indicator methyl red has a $K_{a}$ = $1 \times 10^{-5}$. Its acidic form is red while its alkaline form is yellow. If methyl red is added in a colorless solution with a $pH = 7$, the ...
31
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1answer
7k views

When is it true that more nodes equals higher energy?

Consider all the MOs of some isolated molecule. (It could be a single atom too; I'll use MO to refer to AOs as well.) Number them in increasing order of the number of nodes (node = surface where the ...
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0answers
403 views

How do I measure the density of a cellulose acetate membrane?

I've been playing around with filtration methods, and got my hands on a casting machine for this purpose. My first mission was to find out how porosity can affect filtration. To see this for myself, ...
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3answers
511 views

What does the hydrolysis of a salt tell us about its basic/acidic character?

I'm curious to know how basicity and acidity arises when a salt or covalent compound is dissolved in water.
5
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1answer
195 views

What stable arrangements of hydrogen-bonded water exist in the range of 4-20 water molecules?

Water clusters made up of various numbers of water molecules have been described. Are all of these structures theoretical? What experimental evidence supports any of these structures? How does the ...
2
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2answers
855 views

Bombarding atoms with electron gun?

Just to explain this question in a better way just think about the Rutherford's experiment(the alpha particle bombarded on Gold foil) be conducted using a electron gun in place of the Alpha one.. So ...
3
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0answers
54 views

Other than heating, is there any evidence that normal RF radiation (say, microwave range) can affect chemical reactions?

There's been a lot written (and debunked) about alleged biological effects from RF radiation, even when it's too low powered to cause heating effects or ionization. Is there any chemical reason to ...
8
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1answer
894 views

how are the frequencies at a local maximum of PES like?

On the potential energy surface, if you find a local maximum and calculate its frequencies in Gaussian or something like that, will you get all negative frequencies or all positive frequencies? I know ...
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2answers
81k views

Is there an easy way to remember charges on ions?

I have a chemistry test coming up and I might need to know the charge that goes with the different ions like $\ce{SO4}$ has $-2$, $\ce{NO2}$ is $-1$ and $\ce{PO4}$ is $-3$. Is there an easy way to ...
2
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1answer
836 views

Wavelength of X-rays

What will be the wavelength of X-ray if we apply a potential difference of , say 20 KV across the ends of the x-ray tube ? Alright, i started with the modified de-broglie equation $$\Lambda=\frac{h}{\...
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1answer
5k views

How to dissolve grass/leaves without affecting enclosure?

I've got two questions: What sort of compound can dissolve grass/leaves fastest without leaving "much" trace? What sort of enclosure is required for this to be doen safely and without damaging the ...
4
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1answer
159 views

Sign of the work done during a reversible compression

The work done during a reversible compression - if $V_\mathrm{i} = V_1$ (initial) and $V_\mathrm{f} = \frac{1}{6}V_1$ (final) - of an ideal gas is? I chose $1.8 p_1 V_1$. Is it right or should it be $...
5
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4answers
13k views

Why is the enthalpy of vaporization greater than the enthalpy of fusion?

Why is the molar enthalpy of vaporization of a substance larger than its molar enthalpy of fusion (at constant pressure); for example, in the case of ice and water.
8
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1answer
10k views

How does intramolecular hydrogen bonding cause the molecules to be separated from each other?

I learnt about intramolecular hydrogen bonding today, which occurs between molecules such as ortho-nitrophenol. What I was told is that in case of intramolecular bonding, the molecules separate from ...
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1answer
381 views

What is the mass of 1 Liter of ethylene at 2000 bar pressure?

I was wondering the weight of 1 liter of ethylene at 2000 bar and 310 Kelvin? I have tried to just multiply the weight at 1 bar with 2000 but I don't think i got the correct answer because the answer ...
9
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1answer
6k views

What is Sodium Chloride like in gas state?

Since sodium chloride is sodium and chlorine atoms bonded as a lattice and there are no discrete molecules, doesn't that mean in gas state, sodium chloride is simply sodium and chlorine atoms separate ...
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1answer
8k views

What is the simplest structural unit of an element or compound?

From "Smarter than a 5th Grader": What is the simplest structural unit of an element or compound? molecule, atom, neutron, proton For covalent compounds, the answer would ...
6
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3answers
358 views

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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3answers
2k views

Why isn't neptunium used in nuclear reactors in nuclear power plants?

Why isn't neptunium used in nuclear reactors in nuclear power plants? Uranium is, and plutonium is. But neptunium isn't and it is in the middle of them. Is it like it is too hard to make it do ...
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1answer
428 views

How can we say that one mole of a substance contains avogadro number of particles?

I just want to know, what was the procedure through which the value of one mole of a substance was considered as a an aggregate of $6.023\cdot10^{23}$ particles. Secondly, how do we calculate the ...
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2answers
132 views

Chemical reactions in SFE?

What are the chemical reactions and/or chemical processes that take place during SFE(supercritical fluid extraction)? Namely supercritical $\ce{CO2}$.
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2answers
102 views

Reconciling the units of pH calculation

As part of a simulation I am developing I have an acid in aqueous solution represented as a concentration field of mass density (units g/L) at various points in ...
3
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2answers
661 views

Plot of Arrhenius Equation with temperature

I saw the following plot of the Arrhenius Equation on Wikipedia (cc-by Zivilverteidigung and Matthias M.). It is a concave upwards graph, but according to the equation $$k= A \mathrm e^\frac{-E_\...
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1answer
284 views

Kinetics of interstellar chemistry: Applying steady state to formation of H₂

I am trying to solve problem 2 from the 2009 International Chemistry Olympiad (IChO), which is as follows: If two atoms collide in interstellar space the energy of the resulting molecule is so ...
21
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3answers
25k views

Why are solids and liquids not included in the equilibrium constant? What about in a reaction rate calculation?

Take for instance the reaction $$\ce{H2(g) + I2(s) <=> 2HI(g)}$$ The equilibrium constant would not include the solid $\ce{I2}$, but why is this? I have read that its concentration is a ...
2
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1answer
227 views

Solar still and how it works

I use a solar still that holds 182 cubic feet of water. Here is how it works: There is an insulator on both sides of the metal bowl. On the outside it covers the whole thing. on the inside it covers ...
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1answer
2k views

Units for dissociation constant and relationship to Gibbs Free Energy

How does one "convert" between an equilibrium constant calculated from the Gibbs free energy for a dissociation reaction and experimentally determined dissociation constants? $$ \Delta G^\circ=-RT\...
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1answer
1k views

Why does the lone pair of phosphine not contribute to its dipole moment?

Unlike ammonia, the lone pair of phosphorous does not add to the dipole moment of phosphine. My textbook says this is due to the presence of lone pair of phosphorous in $\ce{PH3}$ in an s-orbital. I ...
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2answers
38k views

How does a lone pair of a central atom affect the dipole moment?

Dipole moment is the degree of polarity, i.e. the seperation of positive and negative charges. But I am not getting the intuition why and how lone pairs affect the polarity and dipole moment. I cannot ...
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1answer
248 views

How can we calculate enthalpy change in a closed tank containing methanol adsorbed by activated carbon?

Here's the problem in the simplest way: I have a closed box containing methanol adsorbed by activated carbon. The box is made from copper. A pipe is connected to that box, which has condenser on the ...
3
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1answer
920 views

How to determine the molecular formula of a compound given its molecular mass and mass percentage contribution of the involved elements?

Hydralazine is a drug used to treat heart disease. It is $59.99\%$ carbon, $5.03\%$ hydrogen, and $34.98\%$ nitrogen and has a molecular mass of $160.178$. What is the molecular formula for ...
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0answers
29 views

Simulating enzymatic change rates of Carbonic anhydrase

I'm trying to simulate effects of carbonic anhydrase on cellular pH as caused by changes in bicarbonate. I assume a bicarbonate homeostatic mechanisms which replenishes intracellular concentrations ...
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2answers
14k views

Does the distance increase as the polarity increases?

According to the dipole moment's definition, as polarity increases the distance between the centres of positive charge & negative charge increases.In the ionic bond ,as the polarity is maximum, ...
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1answer
72 views

Is there a possible effect of mechanical vibration on the stability of organic molecules?

Is there a possible theoretical effect of mechanical vibration on the stability of organic molecules. E.g. some medicines degrade if they are not stored in a fridge, is there a theoretical ...
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3answers
2k views

Finding the initial concentration

The solubility product of $\ce{AgBr}$ is $7.7 \cdot 10^{-13}\:\mathrm{mol^2/L^2}$. What was the initial concentration of $\ce{AgNO3}$ solution, if the precipitation of $\ce{AgBr}$ appears after the ...
2
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1answer
891 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 ...
2
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1answer
11k views

What is defined by part by weight in the definition of equivalent weight?

According to my book, equivalent weight is defined as the ‘number of parts by weight’ of an element that interacts with 1.008 parts by weight of hydrogen. It is dimensionless while gram equivalent ...
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2answers
1k views

Finding overall order of reaction

Recently I've been going through an exercise of Chemical Kinetics and Nuclear Chemistry and right now I am stuck on one question that was previously asked in JEE(Advanced)-2013. The question says, ...
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2answers
8k views

Why do cotton clothes take a longer time to dry as compared to synthetic clothes?

This may be in relation to the $\ce{-O-H}$ group present in cellulose, but I would like to have a more specific answer.
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2answers
14k views

Explanation for the reactions in a saltwater battery with zinc and copper electrodes

I am a physicist, not a chemist. I'm trying to get a basic understanding of the reactions taking place in a battery using a saltwater electrolyte with copper and zinc terminals. I'm writing a general ...
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1answer
40 views

Atmospheric Humidity Effects on Non-water Evaporation

Does evaporation of non-water liquids into the atmosphere vary with atmospheric humidity?
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1answer
124 views

Empirical and Molecular Formulae

I'm not a chemist, and nor do I study chemistry so please try to be gentle. Glucose has the molecular formula $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$ and the empirical formula $\mathrm{C}\mathrm{H}...
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3answers
1k views

Reduce sizing of molecule - Oxygen

Can the size of molecule oxygen reduce smaller? If yes, how is that possible? Is it related to proton and electron surrounding the nucleus?
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2answers
3k views

Calculating the pH of a dilluted aqueous KOH solution

Calculate $\mathrm{p}\ce{H}$ of an aqueous solution of $0.01\:\mathrm{nM}~\ce{KOH}$ in water. I think that water also has $\ce{OH-}$ ions in concentration of $10^{-7}\:\mathrm{M}$ (since $\mathrm{p}\...
3
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1answer
376 views

Specific Heat of Water Solution

If we add an ionic solute to water, will the specific heat of the water be increased or decreased? I understand that the specific heat is a measure of how much energy we must add to water for the ...
2
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1answer
109 views

How does polarimetry account for the orientation of the molecules?

If you have some sample in solution (of a pure R substance), wouldn't the individual molecules all have a random orientation in space? Or do the photons emitted into the solution cause all of the ...
2
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3answers
390 views

Hess Cycle, determining enthalpy change of formation

I am asked to find the enthalpy change of formation of the following: $$\ce{N2 + 1/2O2 -> N2O}$$ I am given the following enthalpies of reaction: \begin{align} \ce{C + N2O &-> CO + N2} &...
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1answer
3k views

Finding out the number of atoms in the sun.

This is the question from the text book: This is what I did, since it worked with all the previous questions (similar to this). $$ \frac{\frac{4}{3}\pi(7*10^8)^3*1.4}{1.008} * 6.022*10^{23} $$ ...