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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How compressibility factor is introduced in Clapeyron equation?

I'm reading section Experiment 13 Vapor Pressure of Pure Liquid in Experiments in Physical Chemistry [1, p. 200]: For the case of vapor–liquid equilibria in the range of vapor pressures less than $\...
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Rubber permeability of hydrogen to air

I am currently studying permeation of rubber film in a university practice group. The problem is to evaluate the permeation of hydrogen gas filled in a meteorological balloon placed in the air, but ...
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Can a reaction produce more products than reactants? [closed]

Q:What volume of propane is burnt for every $100 \mathrm{~cm}^{3}$ of oxygen in the reaction? $$ \mathrm{C}_{3} \mathrm{H}_{8}+5 \mathrm{O}_{2} \rightarrow 3 \mathrm{CO}_{2}+4 \mathrm{H}_{2} \mathrm{O}...
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Vapor pressure in closed systems (2 and multiple components)

Hi there I am currently struggling to understand how vapor/liquid systems work in general. Specifically, I have two qualitative questions. Suppose we had a closed system, half of it filled with just ...
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Usage of AC to measure the conductivity of ionic solutions

there was this statement in my chemistry textbook.... However, for measuring the resistance of an ionic solution we face two problems. Firstly, passing direct current (DC) changes the composition of ...
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3 answers
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Do exothermic reactions also absorb heat?

As I have read that every reaction(endothermic or exothermic)requires activation energy. So is it correct to say that even exothermic reactions absorb heat? I am asking this because it is always ...
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Can the expression be represented as a total differential?

I should determine whether the following expression represents a total differential: $$\mathrm{d}f(x,y) = (\ln y) \,\mathrm{d}x + \frac{x}{y}\,\mathrm{d}y$$ But with the following method (physical ...
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Questions on Third Law of Thermodynamics

Third Law of Thermodynamics reads: at absolute zero , the entropy of a perfectly crystalline substance is zero. (https://simple.wikipedia.org/wiki/Third_law_of_thermodynamics) And considering the ...
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Does a metal being "soft" equal being able to scrape onto paper?

When you scrape aluminum onto paper, it makes a faint mark. The question is, does softness of a metal correlate to how well a mark shows up when you scrape it onto a surface such as paper?
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Calculating internal energy of fragment from $D_0$, photon energy and interval energy + velocity of other fragment

I am trying to solve the following: We consider a photodissociation of a molecule into two fragments. The energy available to the products can be calculated from the bond dissociation energy and the ...
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Simultaneous electrolysis on applying a suitable amount of potential difference

This question was asked in the JEE in 2020: $\pu{250 mL}$ of a waste solution obtained from the workshop of a goldsmith contains $\pu{0.1 M}$ $\ce{AgNO3}$ and $\pu{0.1 M}$ $\ce{AuCl}.$ The solution ...
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How did we find relative atomic masses in 18th century or early 19th century? [duplicate]

The atomic masses of atoms or relative atomic masses were known in the 19th century. But how did they actually calculate that relative atomic mass? What I think is that if we have a sample of an ...
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3 votes
2 answers
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When doing free radical substitution, is the free radical a catalyst?

Consider a simple free radical substitution's propagation step for $\ce{CH4}$ to $\ce{CH3Cl}$: $$ \begin{align} \ce{CH4 + Cl^. &-> CH3^. + HCl}\tag{R1}\\ \ce{CH3^. + Cl2 &-> CH3Cl + Cl^.}...
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1 answer
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Writing rate of disappearance and rate of appearance using rate law [closed]

I have studied that rate of disappearance and rate of appearance is the change in concentration of reactants and products (respectively) with respect to time. Thus, $$\text{ROD} = -\frac{\Delta c_R}{\...
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Can the environment of a molecule affect its HOMO LUMO gap?

For example, if a particular molecule is inside a particular protein, can its absorption maxima change with respect to the isolated molecule? Also, within the same protein, can the molecule's HOMO-...
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Assuming 2O3 (g) → 3O2 (g), how much oxygen will be formed within 5.50 s for a reaction rate of 0.250 M/s?

Context: The rate of appearance of $\ce{O2}$ in the reaction: $\ce{2O3 (g) -> 3O2 (g)}$ is $\pu{0.250 M/s}$. So, over the first $\pu{5.50 s}$, will it form $\pu{1.38 M}$, or $\pu{4.13 M}$ of oxygen ...
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Chemical equilibrium graph [closed]

How can we determine which reaction belongs to which graph. I mean in the above pic . We can observe two graphs and 2 equations. But there is no link between the two . Both the reactions proceed till ...
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What is the structure of sodium chloride in the liquid state?

I understand that sodium chloride when solid, is a lattice, so NaCl there is an empirical formula,(so, expresses that the ratio of Na to Cl is 1-1), and not a molecular formula expressing exact ...
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Any Open-Source, Free Software That Can Be Used to Computationally Calculate Binding Affinity Between Two Molecules? [closed]

There are programs out there which calculate the binding affinity between a ligand and a target protein (Autodock 4, Autodock Vina, Chimera... etc). Is there any analogous program that can be used to ...
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5 votes
2 answers
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Dissolution of sugar in water and its temperature dependence

As far as I can remember, I was taught in 6th grade that warm water would dissolve sugar with greater ease than cool water. In 11th grade, I was taught that Hydrogen Bonding is the reason behind ...
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1 answer
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How to find the empirical formula from mass percentages of oxides [closed]

Say you've given an element X and it makes two oxides. The first oxide is $X_\mathrm{4}O_\mathrm{6}$ and the mass percentage of oxygen is 43.7%. In the second oxide, the mass percentage of X is 43.7%. ...
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DLVO Theory of Colloid Stability

DLVO theory gives the curve of potential energy vs distance of two colloid particles. Potential energy curve is derived for colloids being only electrostatically stabilized and not sterically. Looking ...
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1 answer
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Question on Graham's law of diffusion

Identical balloons are connected through identical valves with two identical cylinders. One cylinder contains gaseous helium and the other gaseous nitrogen. Both the gases may be assumed ideal, and ...
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5 votes
1 answer
133 views

How can we find the normalised wave function for this particle?

A particle moving on the x-axis has a probability of $1/5$ for being in the interval $(-d-a,-d+a)$ and $4/5$ for being in the interval $(d-a,d+a)$, where $d \gg a$. The normalised wave function for ...
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At what pressure will ambient atmospheric air liquify? [closed]

At what pressure will ambient atmospheric air liquify? (Ambient Earth atmosphere at say five foot above sea level. From any specific point on Earth, since it would vary from point to point due to ...
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Stability of Microemulsions

Unlike emulsions, microemulsions are thermodynamically stable. Its stability is often explained by entropy changes brought about by dispersing liquid in another liquid, however this can't be the whole ...
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1 answer
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Confusion regarding continuity of state

I was reading about Andrew's isotherms and about the continuity of state. What confused me was the continuous conversion of gaseous state to liquid state. Now my textbook says that by keeping volume ...
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2 votes
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How to visualize an endothermic/exothermic reaction? [closed]

Let’s say X and Y bond together to create XY, where this reaction is exothermic. What I’m visualizing in my head is X and Y floating about with certain speeds, which contributes to their kinetic ...
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2 votes
2 answers
432 views

What does n(Na2CO3) mean?

In my book, $n(\ce{Na2CO3})$ was used to indicate the number of moles of $\ce{Na2CO3}$ without any clarification. Is it common knowledge among chemists that $n(\ce{Na2CO3})$ indicates the number of ...
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How does the Standard Cell potential of the Nernst equation work? [closed]

$$ E = E^\circ - \dfrac{RT}{nF} \ln Q $$ For calculations, the standard cell potential is typically given with a reference page, using elements at standard conditions. While doing an experiment with ...
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Can uv light cause heterolytic cleavage?

All sources I've read stated that UV-light can only cause homolytic cleavage (homolytic fission), producing radicals while not mentioning whether it was possible for it to cause heterolytic cleavage ...
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1 answer
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Matrix elements evaluation in Hartree-Fock method

In Roothaan's matrix formulation of the Hartree-Fock method, we eventually must evaluate the elements in the Fock matrix in the form: $$F_{\mu\nu} = \langle \mu | {-\frac{1}{2}}\nabla^2 | \nu \rangle ...
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1 answer
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Normalized absorbance/transmittance definition [closed]

In the absorption spectroscopy we can calculate transmittance $T$ of a given sample by comparing how the intensity of the incident beam $I_{0}$ is decreased with the distance (Lambert-Beer Law). $A = -...
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2 votes
1 answer
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Lennard-Jones Potential repulsion by nucleus nucleus or Pauli repulsion?

I read different things, some textbooks say that the repulsive part of the lennard jones potential is due to the repulsion of the nuclei when they are too close, others say it is due to the pauli ...
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6 votes
3 answers
595 views

What material properties are unpredictable (not reproducible) but can be measured consistently and at a low cost?

I'm looking for a process to create a material which has some easy to measure properties. These properties should be consistent over a long period. It should be very hard (expensive) to predict/...
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4 votes
1 answer
166 views

Can two noble gases attract each other?

If two hydrogen atoms are far apart, they have no effect on one another. But as they are bought closer together, they begin to excerpt an effect. The two nuclei, having the same positive charge, repel ...
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4 votes
0 answers
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Why is supersaturated sodium acetate so (meta)stable?

Sodium acetate is a common example used in general chemistry lectures to illustrate the idea of supersaturation, and that precipitation of a supersaturated solution can be initiated by a seed crystal. ...
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5 votes
1 answer
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Can I use the Winkler method as a way to measure the rate of photosynthesis?

I want to make an investigation where I measure how the color of light affects the rate of photosynthesis. The idea is to put an Elodea plant in a test tube and shine with different color of light ...
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How can a system that has phases of different compositions be in equilibrium?

I understand determining conditions of equilibrium for a unary system; each of the separate phases can be treated as a one-phase system with its own set of extensive and intensive properties. However, ...
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1 vote
1 answer
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Suppressing flammable foam formation in electrolysis

I often use electrolysis to remove rust and other junk off of steel parts. My general setup is: Electrolyte: Sodium bicarbonate + distilled water. Anode: Plain carbon steel Cathode: Carbon steel, ...
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2 votes
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Formula for collision frequency and mean free path

We were studying collision frequency and mean free path today, and in it, we got the equations of collision frequency as: $$Z=\sqrt 2 \pi \sigma^2v_{rms}N$$ where $N$ is the number density, equal to $...
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1 vote
1 answer
60 views

what are the differences between reversible cells and rechargeable cells?

My chemistry textbook says daniel cells are reversible, but not rechargeable. Why is it that all reversible cells are not rechargeable? Are all rechargeable cells reversible? why/why not?
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3 votes
0 answers
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Problem with partition function when calculating equlibrium constant?

For example a reaction is given as ($\pu{T = 1000 K}$), $$\ce{2Na(g) <--> Na2 (g)}$$ The equilibrium constant, $$\ce{K_{c} = \frac{\frac{q_{Na_{2}}}{V}}{(\frac{q_{Na}}{V})^2}}$$ But when ...
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What is reversible change for ideal gas?

What are the reversible and irreversible changes for an ideal gas? Is it the change that keeps the ideal gas law during the change? Is any reversible change a sum of changes satisfying the ideal gas ...
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How Does Peroxide + UV = Oxidation?

I restore shoes, & we have this method for oxidizing the translucent soles to get them to look new again. The process is: clean surface Apply 40 Volume peroxide cream Place under UV Growlight. I ...
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Gibbs energy of electron transfer

the reaction Gibbs energy of a cell: $\Delta_rG^o=-nFE^o$ and the Gibbs energy of photoinduced electron transfer: $\Delta_{ET}G^o=N_A\{e[E^o(D^{+.}/D)-E^o(A/A^{-.})]+\omega(D^{+.}A^{-.})-\omega(DA)\}-\...
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1 vote
2 answers
127 views

How to prevent hydrogen embrittlement in SmCo magnet?

We have a measuring apparatus that incorporates a samarium-cobalt (SmCo) magnet. Normally this is exposed to various gases under test. However, a problem has arisen with hydrogen, namely the magnet ...
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1 answer
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Question regarding Entropy [closed]

I had some doubts regarding the concept of entropy. My first doubt was Entropy is defined as $ dS = dQ _{rev}/ T $ yet my textbook says that entropy is a state function. Isn't it the definition of a ...
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3 votes
1 answer
187 views

How can surface excess be negative?

If we have interphase of two phases $\alpha$ (water) and $\beta$ (air), surface excess is defined as $$\Gamma_i = \frac{n_{i,\mathrm{tot}} - n_{i,\alpha} - n_{i,\beta}} A = \frac{n_{i,\mathrm{int}}} A,...
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Problem understanding the rate of reaction of reversible reactions

Case 1: $$\ce{CH_3COOH + NaOH<=>CH_3COONa + H_2O}$$ At equilibrium, there remain extremely small concentrations of the reactants (acetic acid and sodium hydroxide), and comparatively large ...
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