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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Approximating entropy change in a reaction using Arrhenius equation

I am a high school student.Recently my teacher finished teaching the chapter Chemical kinetics in which I have gone through Arrhenius equation.Can we estimate the change in entropy using it? I have ...
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17 views

The minima of minimum boiling azeotropes

This is a very basic doubt, so I'll be really brief about it. The discussion I raise is particularly about minimum boiling azeotropes but it's understood that whatever I ask is about the general ...
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Applying Bohr's model for Helium atom

Consider the following atomic model for Helium. Helium contains 2 electrons revolving in circular orbit around the nucleus,in such a way that there is minimum possible repulsion between them.Calculate ...
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How does ammonium nitrate explode on its own?

I thought ammonium nitrate was an oxidizer that needed to be mixed with fuel to form a high explosive (e.g., ANFO). But apparently there have been accidental explosions involving just the "...
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1answer
41 views

Thermodynamics of chemical reactions “at constant pressure”

Chemical reactions occur at constant temperature and pressure. Consider a gaseous, equilibrium reaction: $\ce{2NO2(g) <=> N2O4(g)}$. Most questions/textbooks formulate such questions by stating:...
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Rate law expressions [closed]

Question For the reaction, $$\ce{2NO(g) + 2H2(g) -> N2(g) + 2H2O(g)}$$ The rate expression can be written in the following ways: $\frac{\mathrm{d}[\ce{N2]}}{\mathrm{dt}} = \mathrm{k_1}[\ce{NO}][\...
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2answers
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Analysing reversible processes

A reversible process is a process in which the system is in mechanical and Thermal equilibrium with its surroundings. Consider a simple thermodynamic system: a gas in a vessel, with a piston (free to ...
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2answers
34 views

Thermal equilibrium in reversible processes

In whatever resources I have consulted to study reversible thermodynamic processes, a common statement seems to be : The system and surroundings (if the boundary allows) are in mechanical ($P_{sys}=...
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1answer
38 views

Conductivity of molten or aqueous salts

If there is a 1M aqueous solution of 1 liter NaCl (aq), and the molar conductivities of the solution and the chloride ions were found to be $x$ and $y$ respectively, is it accurate to say that the ...
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2answers
59 views

rate of reaction and RDS

An article on Khan-Academy, states the following: The overall reaction rate is determined by the rates of the steps up to (and including) the rate-determining step Here, it says that rate is ...
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Illustrating moles with sand grains, Are there more moles of SiO2 in a grain than moles of sand on the earth

I have been trying to understand the scale of atoms, thinking about sand grains as an example. With approximately $7.5\times10^{18}$ grains of sand on the earth that is $1.25\times10^{-5}$ moles of ...
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1answer
58 views

A theoretical chemistry question about elements and their presence over time [closed]

I'm not a chemist myself, but I can't think of a better place to get some insight about elements and chemistry than from people who live and breathe it here on stackexchange. This is not any kind of ...
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Relation between Gibbs free energy and the order of a reaction

I was reading a biophysics book and at the chapter for membranes it was talking about the melting of the lipid bilayer. Now I don't know much about this topic but this phrase strikes me as kind of odd:...
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1answer
47 views

Equilibrium constants and concentrations [closed]

I know that concentrations of pure solids and liquids must be ignored in equilibrium constant expression, as they are constant. However in this reaction, they have taken the concentration of compound ...
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129 views

Number of moles of acidified potassium dichromate required to liberate 6 moles of iodine from an aqueous solution of iodate ions

I came across this question in a recent exam I had taken: How many moles of acidified $\ce{K2Cr2O7}$ is required to liberate 6 moles of $\ce{I2}$ from an aqueous solution of $\ce{I-}$ ? So this is ...
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42 views

Using Beer-Lambert law to calculate light intensities

Supposing the mean absorption coefficient of seawater in the visible region is 0.8 m$^{-1}$, calculate the depth at which a diver will experience half the surface light intensity. I know that you have ...
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1answer
30 views

Formation of Goethite

Probably a simple question: When you're mixing potassium hydroxide ($\ce{KOH}$) with iron nitrate ($\ce{(FeNO3)3}$) to form ferrihydrate, does the temperature have to be below $\pu{60 ^\circ C}$?
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How is the temperature in which vapor pressure is equal to atmospheric pressure the boiling point of the liquid? [duplicate]

I was just learning about vapor pressure and got very confused. Vapor pressure was defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given ...
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How can ReF7 hybridization be explained? [closed]

As per the diagram, The compound ReF7 has a pentagonal pyramidal or distorted octahedral geometry and has sp3d3 hybridization. But, hybridization can theoretically occur in degenerate orbitals of ...
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47 views

The graph of log(x/m) versus log(p) in surface chemistry [closed]

In surface chemistry, the graph of $\log(x/m)$ and $\log(p)$ is a straight line with slope $1/n$ but $n$ is constantly changing. Then, why is the graph of $\log(x/m)$ versus $\log(p)$ a straight line ...
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Which will be more effective electrolyte for Fe(OH)3 solution? Is it K2SO4 or K2Cr2O7? [closed]

$\ce{Cr2O7}$ and $\ce{SO4}$ both have same charge which is $-2$. Then which will be more effective?
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1answer
40 views

Van der Waals force in o-nitrophenol [closed]

We know that in p-nitrophenol, there is intermolecular h-bonding but how do we come to know that there is Van Der Waals force of attraction in two molecules of o-nitrophenol?
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306 views

Why is the molar entropy of hexane lower than that of butane?

Entropy is dependent on the complexity of the molecule. Due to this, I expected entropy to increase as the complexity of the molecule increased. According to p 918 of Atkins' Physical Chemistry (9th ...
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Software for modelling decomposition reactions

What are some good softwares that can model a decomposition reactions? I have a reaction of H2O2 decomposing on metal exchange hexaaluminate catalyst. The catalyst is present in a packed bed thruster. ...
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Fate of compounds after radioactive decay [duplicate]

Let us say there is a $\ce{CO2}$ molecule containing $\ce{^{14}C}$ isotope. $\ce{^{14}C}$ undergoes decay to form $\ce{^{14}N}$. What happens to the molecule?Does it form $\ce{NO2}$? How are the ...
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Why does oxygen convert to ozone in stratosphere vis a vis spontaneity and gibbs free energy? [closed]

I am a high school student trying to wrap my head around the second law of thermodynamics for the past few days to no avail. Having only a cursory knowledge of calculus, and chemistry and physics in ...
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1answer
34 views

Molality of solution to be used when finding water separated from solution as ice

Question $\pu{1 kg}$ of a solution of cane sugar is cooled and maintained at $\pu{-4 ^\circ C}$. How much ice will separate out if molality of solution is $0.75$? $K_\mathrm{f} \ \text{(water)} = 1....
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Gas chemistry preasure [closed]

5.00 g of CO2 gas occupy a volume of 5.4 L at a pressure of 350 mm Hg. What will the volume of the gas sample be if the pressure is changed to 70.0 kPa?
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1answer
47 views

Feasibility of a Reaction [closed]

I understand for a reaction to be feasible, $\Delta$H needs to be negative and $\Delta$S positive. But in terms of Gibbs free Energy Change, without considering kinectic factors, If $\Delta$H is ...
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3answers
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How to simulate a Lorentzian broadened spectrum in MATLAB?

I'm trying to simulate the 2nu2 band of HCN in MATLAB. I generate a stick spectrum from the data I have (taken from the HITRAN database) and then use conv() to ...
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1answer
60 views

Calculation of rupture force in a covalent bond

Is there any way to theoretically or mathematically calculate the rupture force of a covalent bond? One of the articles I saw said that it is the maximum derivative of the potential energy curve. Is ...
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2answers
64 views

Effect on mass when decreasing pressure in equilibrium reaction

For example, if we have the reaction: $$\ce{A + B <=> C}$$ And the volume is decreased, the pressure would increase. Hence, according to Le chatelier's principle, the system will partially ...
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1answer
73 views

Calculating the viscosity of water using particles

There are two particles with radius 0.212 μm. The particles are in a thin liquid film and the microscope can only detect movement in the $x$- and $y$-axis. The temperature is 25 °C. $$ \begin{array}{c|...
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37 views

Stoichiometric calculation of composition of a compound

I have a question from a high school review package. I don't need the answer, but one thing that is bugging me is that, I feel as if I do not understand the question at all. I don't know what it wants ...
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2answers
186 views

Comparing equilibrium constants between acetone and benzaldehyde in nucleophilic addition reaction

My teacher told me that the $K_\mathrm{eq}$ of acetone is greater than that of benzaldehyde in nucleophilic addition reaction. But I am not able to understand how is this possible. Acetone has a +I ...
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1answer
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How is the formula of mean activity coefficient derived?

The mean activity coefficient is defiend as follows: $$\gamma_\pm = (\gamma_+\gamma_-)^{1/2}.\tag{1}$$ If Debye-Hückel equation $$-\log\gamma_i = 0.5z_i^2\mu^{1/2}\tag{2}$$ is used, then the mean ...
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1answer
39 views

Equilibrium constant for heterogeneous equilibria having aqueous as well as gaseous reactants

Suppose we have a heterogenous equilibrium : $$\ce{A(aq) +B(aq) <=> C(g) +D(aq)}$$ Which equilibrium constant is used here? Both pressure and concentration terms are there. So, according to me, ...
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1answer
81 views

Sign of change in enthalpy and change in entropy

Why is it wrong to assert that the change in entropy and the change in enthalpy must always have the same sign? What makes me think that they must have the same sign is the fact that every reaction ...
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Reducing pressure and calculation of concentrations at equilibrium

For the equilibrium $$\ce{PCl5(g) <=> PCl3(g) + Cl2(g)}$$ $$ K_c = \pu{4.16E-2 mol dm^{-3}}~\text{at}~\pu{250 °C}$$ $$[\ce{PCl3}] = [\ce{Cl2}] = \pu{0.204 mol dm^{-3}}$$ If the pressure of ...
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The relation between q and T when the volume is constant [closed]

$$ \begin{align} q_V &= ΔU \tag{1}\\ q_p &= ΔH \tag{2}\\ C_V &= \frac{\mathrm dq_V}{\mathrm dT} = \left(\frac{\partial U}{\partial T}\right)_V \tag{3}\\ C_p &= \frac{\mathrm dq_p}{\...
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1answer
121 views

Converting fractional coordinates into cartesian coordinates for crystallography

So let's say for a given molecule I have the volume of a unit cell, the shape of the unit cell (monoclinic, cubic, etc), the cell angles alpha, beta, and gamma, the cell lengths a,b, and c, and a list ...
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2answers
72 views

Calculation of pH in acid base reaction

This problem(from ionic equiibrium) states: We are given $\pu{40 mL}$ of $\pu{0.1 M}$ $\ce{HCl}$ and $\pu{10 mL}$ of $\pu{0.45 M}$ $\ce{NaOH}$ in two separate beakers. These two solutions are mixed. ...
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2answers
175 views

Disproportionation of silver(I) in aqueous solution

Use the following equations to predict whether or not $\ce{Ag+}$ ions will disproportionate in solution: $$ \begin{align} \ce{Ag+(aq) + e- &-> Ag} &\qquad E^\circ = \pu{+0.80 V}\\ \ce{Ag^2+(...
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1answer
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Finding the ratio of rate constants [closed]

A group of mountain climbers set up a camp at a $\pu{3 km}$ altitude and experience a barometric pressure of $\pu{0.69 atm}$. They discover that pure water boils at $\pu{90 ^\circ C}$ and that it ...
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33 views

Why does Le Chatelier's principle work for temperature changes? [duplicate]

I do science tutoring. One of my students asked me why Le Chatelier's principle works, and I was able to explain it for concentration and pressure by referencing the law of mass action, but I could ...
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1answer
78 views

Is it easier to oxidise iron(II) to iron(III) in acidic or alkaline solution? [closed]

Is it easier to oxidise $\ce{Fe^2+}$ to $\ce{Fe^3+}$ in acidic or alkaline solution? $$ \begin{align} \ce{Fe &-> Fe^2+(aq) -> Fe^3+(aq)}\\ \ce{Fe &-> Fe(OH)2 -> Fe(OH)3} \end{align}...
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42 views

Significance of pV work in enthalpy

If we already have $pV$ work included in the internal energy $U = q + w,$ then what is the $pV$ work in the equation for enthalpy $H = E + pV?$
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88 views

Cis and trans electrodes

I have come across use of the terms cis and trans electrodes in the context of nanopores and driving charged biomolecules through a pore using an electric field [1]: FIG. 1. Drawing of the cis ...
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1answer
91 views

An expression for equilibrium constant of isotope reaction

Consider the isotope exchange reaction: $$\ce{C ^{16}O + 1/2 ^{18}O {}^{18}O <=> C^{18}O + 1/2 ^{16}O^{16}O}$$ The equilibrium constant for the reaction is: $$K=\frac{\prod (a_i)^{n_i}_{products}...
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1answer
89 views

Expression for Gibb's free energy change for a cell reaction

According to Chemistry Libretexts, the Gibbs free energy change of a cell reaction is related to the cell voltage as $$ \Delta G = -nFE,$$ where $n$ is the number of moles of electrons passed and $F$ ...

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