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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3answers
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How can Ellingham diagrams be linked to Gibbs energies of formation?

My textbook quotes the following as the limitation of Ellingham diagram: The interpretation of $\Delta G_\mathrm{f}^\circ$(standard Gibbs free energy of formation) is based on $K$ ($\Delta G_\...
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2answers
58 views

Pressure turning out to be zero?

I was studying for my freshman chemistry course, and ran into a mind-boggling contradiction. We know, at equilibrium, entropy is at a maximum: $$\left(\frac{\partial S}{\partial V}\right)_U=0$$ From ...
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Proving a thermodynamic relation between $(\partial H/\partial T)_p$ and $(\partial U/\partial T)_V$

(This question is taken from Problem 1.1(b) of the book Chemical Thermodynamics: Principles and Applications.)$\require{begingroup} \begingroup \newcommand{\pd}[3]{\left(\frac{\partial #1}{\partial #2}...
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Rate law: Iodine clock reaction [closed]

What is the rate of the reaction if $\frac{\Delta[\ce{HSO3-}]}{\Delta t} = \pu{-0.0077 mol L-1 s-1}$? The entire set up is: $$\text{Rate} = \frac{-\Delta[\ce{IO3-}]}{\Delta t} = -\frac{1}{3} \times ...
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About the Arrhenius equation [closed]

P I am talking about the arhennenius equation That what would happen if the constant Kis less than A in the equation According to me will the activation energy becomes less than zero or something ...
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5answers
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Why did life end up with the big 4 elements, and specifically nitrogen?

This question is mostly about the human body, but it's also about life in general. It's not difficult to notice a big different between the abundance of elements on Earth & that in the body. I've ...
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Maximum Value of Monolayer Capacity

What is the possible maximum value of the monolayer capacity? Is it possible for the monolayer capacity to exceed more than $(100)\frac{mol}{g}$ or even $(1000)\frac{mol}{g}$? Any help is highly ...
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Absorption Equilibrium Constant ($K$)

How to calculate the absorption equilibrium constant ($K$) using the numerical value for the equilibrium capacity ($Ce$) and the numerical value for the absorbed capacity ($Qe$)? I try to divide ($Qe$...
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45 views

Looking for color changing reaction to track snow layer depth

I'm trying to find a chemical to mark the position of a snow layer with for detection in future seasons. The substance has to be: 1. Colorless 2. Not water soluble/solid 3. Stable for multiple years ...
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1answer
29 views

Applied Potential and Electrochemical Cell Potential

Electrolysis of molten lithium hydroxide at $\pu{750 K}$ to form lithium metal $$\ce{4 LiOH -> 4 Li + 2 H2O + O2}.$$ Electrolysis will only proceed at an appreciable rate when the applied ...
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+50

What is the precise definition of standard molar entropy?

I understand what the standard molar entropy is, and how to use it in calculations, but I'm interested in understanding exactly how it's defined and measured. My recollection from a long time ago is ...
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Homework - Water evaporation in a sealed container with vacuum [closed]

Let's say I have a container where I extract the air and create a near perfect vacuum. The volume of the container is 100 m^3 In the container there is a large bottle (made of glass) which is filled ...
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How do I find the error in the rate of a pseudo first order reaction (Acid hydrolysis of ethyl acetate) [closed]

How do I find the error in the rate of reaction with the formula given below? Thanks!
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2answers
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Electric double layer formation

What Textbook states about the formation of electric double layer: When silver nitrate solution is added to potassium iodide solution the precipitated silver iodide adsorbs iodide ion from ...
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0answers
48 views

Is there any proven effect of spraying aerosol on evaporation of water? [closed]

Yesterday I was performing extraction of sodium chloride from its saturated solution in water by placing a bowl containing the solution under the hot sun. There wasn't much change in the volume of ...
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27 views

Reference for Hammett acidities of dilute H2SO4?

When $\ce{H2SO4}$ is dissolved in water in little amounts ($<\pu{1M}$), the $\mathrm{pH}$ scale can be used to measure the acidity of the solution. However, in larger concentrations, this breaks ...
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30 views

Symbols for electronic states [duplicate]

When expressing the electronic state of OH, symbols such as $A^2\Sigma^+_s$ and $X^2\Pi_{3/2}$ were used. What do these symbols represent? Thanks for any help! :)
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What is the logic behind the terminology lyophilic and lyophobic colloids?

Its given in my text book that- Colloidal dispersions of starch,rubber,proteins etc are lyophilic colloids whereas colloidal dispersions of metals,sulphides etc are lyophobic in nature. But even ...
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Molecular Kinetic Theory of Gases [closed]

Q (1) / at the same temperature and pressure which of the following gases will have the highest kinetic energy per gram..? a) h2 b) o2 c) ch4 d) n2 Q(2)/at the same temperature and pressure which ...
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2answers
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What are Degenerate Rotational Energy Levels Physically?

I'm in introductory chem, so I don't have much of the physical background to really understand what's going on yet, but we're learning about rotational energy levels, and how some rotational energy ...
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1answer
60 views

Hardy Schulze Rule

There was a question which was asked in JEE Main 2020 held on 8th January. The question was: As per Hardy–Schulze formulation, the flocculation values of the following for ferric hydroxide sol ...
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How to account for the common ion effect on osmolarity quantitatively?

In adjusting the osmolarity of a solution of Benzalknonium Cl, Disodium Editate, and Disodium borate/boric acid buffer to be isotonic (about 290 mOsm), the addition of NaCl showed unexpected behavior, ...
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1answer
49 views

Why Freundlich adsorption isotherms fails at high pressure conditions?

Experimentally it was determined that extent of gas adsorption varies directly with pressure, and then it directly varies with pressure raised to the power 1/n until saturation pressure Ps is reached. ...
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1answer
65 views

How energy is released when chemical bond is formed?

In books it is commonly written that whenever a chemical bond is formed the energy of the molecules/atoms gets lowered and hence energy is released. This is generally explained by diagrams like this ...
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1answer
53 views

On the origin of Gibbs Free Energy

It is intuitive to me that for a spontaneous process involving any system i.e. one occurring without constant human interaction $$ \text{d}S \geq 0 $$ as I can observe increasing energy dispersal in ...
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Why is concentration used as a proxy for activity instead of mole fraction?

I am trying to understand how the Gibbs energy change of a chemical reaction is computed and I do not understand why concentrations (mol/L) are used as a proxy for activity rather than mole fractions (...
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1answer
66 views

What in salt makes ice unable to refreeze? [closed]

I know that salt makes ice melt, but why does salt make the ice not refreeze? I have tried all different kinds of experiments, but I still cannot figure it out. The chloride acid in the salt makes ...
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1answer
67 views

Gibbs energy: the term −TdS. Where does the reversible heat go?

When we have an exothermic reaction as well as a decrease of the entropy in the system after the reaction, why does the decrease in the entropy of the system diminishes the amount of useful work we ...
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1answer
28 views

Is there a name, or any specific jargon for a precipitation equilibrium involving a solid reactant?

Let's say you have some ions in solution, for example Na+(aq) and OH-(aq), and some partially dissolved solid, MgCO3(s), Mg+2(aq) and CO3-2(aq), which precipitates Mg(OH)2(s) until equilibrium. So ...
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2answers
73 views

What repulsion keeps non-hydrogen atoms at a distance: between inner shells or between nuclei?

Bonded or not, when two atoms or ions come closer than the bond distance or the van der Waals distance, the energy increases drastically. What is the underlying cause of that repulsion? The repulsion ...
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2answers
82 views

On the angle subtended between the angular momentum vector and the applied field for a single spin

According to Dr James Keeler of Cambridge University in one of his lectures at Queensland University, the angle theta can be any angle, but I struggle to see how this is true. There are only a certain ...
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Atomic mass, and relative atomic mass, confusion [duplicate]

What I have understood: Atomic mass: average of mass number of isotopes of an element and is measured in amu. eg. 1 atom of Sodium has atomic mass of 23 amu, similarly 1 atom of of Carbon has 12 amu(...
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how is mass of nucleus in carbon-12 more than 12u [duplicate]

The mass of proton on atomic unit scale is 1.00727 amu. The mass of neutron on atomic unit scale is 1.00866 amu. Carbon-12 has 6 protons and 6 neutrons, right? So its atomic mass should be 12....
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On the origin of spin-lattice relaxation

According to P.J. Hore in the Oxford Chemistry Primer "Nuclear Magnetic Resonance" p57, 'the dipolar coupling, modulated by molecular motions, causes nuclear spins to experience time-dependent local ...
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1answer
42 views

Does the prefix Ortho have some significance? [duplicate]

Are orthoboric acid and boric acid one and the same thing or we can not write H3BO3 as B(OH)3?
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How to find the molar concentration of two compounds mixed together in a buffer solution having the Kb and its Ph [duplicate]

Calculate how many milliliters of a $\pu{8.00 \times 10^{−1} M}$ solution of $\ce{NH3}$ and how many milliliters of a $\pu{7.80 \times 10^{−1} M}$ solution of $\ce{NH4Cl}$ are needed to get to a liter ...
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3answers
81 views

Need help understanding Enthalpy

My chemistry textbook says that: Enthalpy (Internal Energy) = chemical potential energy + thermal energy Now, I know that Enthalpy and Internal Energy are different so I really don't understand ...
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0answers
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Effect of drinking on internal energy and entropy of the universe

I have just been doing some questions on thermodynamics and have come across a strange question that I can't seem to grasp. The question asks me to estimate the change in body temperature as well as ...
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0answers
10 views

Is Raoults Law valid if the solute is non volatile but have less vapour pressure than pure solvent?

We know that on adding a non-volatile solute to a pure solvent its vapour pressure increases because of the reluctance of solute to evaporate(i.e. strong intermolecular forces of attraction) Instead ...
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How to calculate the energy to dissociate a bond into neutral atoms?

I am self studying chemistry through MiT ocw 5.111 . On practice exam 2 problem 2 there is a question which states the following ...
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1answer
21 views

How are cells rechargable?

I have learnt that you can test if a reaction is thermodynamically feasible by testing if the cell voltage $E_\mathrm{cell}$ is greater than $0$. Surely, if a reaction is feasible, then the $E_\mathrm{...
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0answers
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LIF spectrum with laser-coupled levels lines as the strongest

Why, if I excited the OH molecule Q-branch transition, my LIF spectrum (recorded during and after the laser pulse) does not result in only Q line being the most prominent, but also P and R lines with $...
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1answer
29 views

Is an amorphous solid a single phase?

Amorphous solid possess short-range order but no long-range order (e.g. amorphous silica, the short-range order is originated from the tetrahedral bonding between Si and O). Is it possible to have ...
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1answer
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Surely distilled water is the answer to a polluted planet [closed]

I have been researching a long time on best water to drink and find that there are so many sources of pollution from industry, farming, agriculture and so forth creating run off into our fresh water ...
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0answers
19 views

Comparing rates of effusion between species

I'm struggling with (i) and (ii). I understand how to do (iii) and (iv) as it is just an application of Graham's Law of Effusion twice and n times (solve for n) respectively. I am starting with rate ...
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1answer
31 views

Electrolysis of Baking Soda separated by semi permeable membrane

I have dissolved baking soda in battery water (de-ionized), in a glass beaker and used a food handling glove (vinyl) as a semi-permeable membrane to separate a graphite electrode from a copper ...
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1answer
74 views

Entropy as a state function independent of the path

When entropy is a state function and the entropy change for a reversible process is $$\mathrm dS_\mathrm{rev} = \frac{\delta Q_\mathrm{rev}}{T} = 0,$$ how can an irreversible process be ...
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39 views

Enthalpy of reaction between ammonia and oxygen

I have to ask this here because I asked literally everybody I know and I still disagree with them. Using the information in the table below, calculate the heat of released from the following ...
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1answer
39 views

Finding molecular formula with limited information given

I have recently stumbled upon a question I can't seem to solve : Chlorine can also be used to synthesise a bromine-containing oxoanion that is mainly used in continuous or batch dyeing processes. ...
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1answer
127 views

Elevation in boiling point of water [closed]

$\pu{1060 g}$ of urea aqueous solution is subjected to heating. It starts boiling at $\pu{100.53 °C}.$ It is heated up to $\pu{102.12 °C}.$ Find amount of water vapourised in grams. (Pure water ...