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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44 views

Intuition for relation between electrode potential and reaction quotient

Consider the following reaction in a galvanic cell: $$\ce{X(s) + Y+(aq) -> Y(s) + X+(aq)}$$ According to the Nernst equation, $$E =E_\circ - \dfrac{RT}{F}\ln\left(\dfrac{\ce{[X+]}} {\ce{[Y+] }} \...
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1answer
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Why is "activity" of gaseous component equal to its partial pressure but that of aqueous component its concentration?

While solving an electrochemistry problem I had to calculate the reaction quotient of this reaction: $$\ce{2Fe(s) + 4H+(aq) + O2(g) -> 2Fe^{2+} (aq) + 2H2O (l)}$$ It turns out to be: $$\ce{Q=\dfrac{...
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1answer
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Is there any relation between reaction quotient and rate constant in the context of order of the reaction?

How many times will the rate of the reaction $$\ce{2 A + B -> A2B}$$ change if the concentration of substance $\ce{A}$ is doubled and that of substance $\ce{B}$ is halved? The given solution takes ...
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Ionic mobilities and conductivities of lithium and potassium cations in acetonitrile–propylene carbonate solution

Recently I calculated the ionic mobility and molar ionic conductivity values for $\ce{Li+}$ and $\ce{K+}$ cations in an acetonitrile–propylene carbonate binary mix solution (8:2 molar fraction ratio). ...
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What is the enthalpy of formation of benzene? [closed]

I was trying solve this question from my book: The combustion of one mole of benzene takes place at $298 \mathrm{~K}$ and 1 atm. After combustion, $\mathrm{CO}_{2}(\mathrm{~g})$ and $\mathrm{H}_{2} \...
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Can a battery be built where several electrodes share the same electrolyte?

If you have two metals i.e. iron / copper and an electrolyte solution you can make a battery. Typically all of the designs have several of these connected in series to boost the output. But I have ...
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Why aren't electrons included in the equilibrium constant expression?

This might be elementary, but why aren't electrons included in the equilibrium constant for a half-reaction? For example, for $$\ce{O2 (g) + 4H+ (aq) + 4e- -> 2H2O(l)}$$ we have $$Q = \frac{(a_\ce{...
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1answer
127 views

Can't fit an exponential curve to the decomposition of hydrogen peroxide

I have carried out an experiment on the $\ce{MnO2}$ catalyzed decomposition of hydrogen peroxide. I would have expected the reduction in concentration to be exponential but when I fit an exponential ...
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1answer
57 views

how to show the coordinate bond in avogadro?

I have this structure figure 1, I want to visualize by Avogadro, but the shape is not as I want like in figure 2 where I used Molden, so how can I make Avogadro draw the coordinate bonds.
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Linear algebra and Hess's law?

I am a high school student taking chemistry who was tasked to solve a large set of Hess's Law problems. Naturally I tried to find a way to get my computer to carry out this repetitive piece of work ...
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1answer
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If something is not hydrophilic, is it necessarily hydrophobic?

Is it possible to create hydrophobic water? Two species are phobic within some medium under some conditions when they don't here together (cohere if they're the same species; adhere otherwise). To be ...
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1answer
96 views

Can we have an equilibrium constant for a reaction at constant volume?

Suppose we have a sealed container (fixed volume) and we introduce two gases $\ce{A}$ and $\ce{B}$. The two reactants $$\ce{A + B <=> C}$$ form another gas $\ce{C}$ with equilibrium constant $K$....
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Is there a parameter for degree of ‘mixedness’

So I was making coffee this morning and when mixing some milk into the black coffee, I wondered if there was some parameter or value in chemistry which describes how well mixed two liquids (or gases) ...
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3answers
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Is it possible to create hydrophobic water?

I recently saw "hydrophobic water" in my school science fair. I have no idea on the procedure of how to make it, so, can I make it? I did google it and read some articles (zero helpful) and ...
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80 views

What does water saturated oxygen mean? [closed]

What does water saturated oxygen mean in this question: The vapour pressure of water at 80º C is 355 torr. A 100 ml vessel contained water saturated oxygen at 80º C, the total gas pressure being 760 ...
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1answer
96 views

Why does adding excess NaOH prove amphoteric nature?

When 3+ hexaaqua ions react with hydroxide ions, the following set of reactions occurs: When we get to stage 3, a neutral ion has formed, and a white precipitate is created. Now, we know that for ...
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2answers
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What is the cathode in NiMH batteries

What is the cathode in $\ce{NiMH}$ batteries? I’m not sure if it is $\ce{Ni(OH)2}$ or $\ce{NiOOH}$. I’m confused because I thought that these batteries are like $\ce{NiCd}$ batteries except better (...
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Units conversion of Henry coefficient in adsorption on solids [closed]

In a database of solid microporous materials I have the Henry coefficient in units of $\pu{mol kg^{-1} Pa^{-1}}.$ How to convert to $\pu{Pa^{-1}}?$ I tried to multiply by the molar mass of the sorbate ...
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1answer
114 views

Are sudden adiabatic expansions reversible or irreversible? (Tyre burst problems)

Encountered Question: The tube of the tyre of a car is filled with air at $\pu{27^\circ C}$ and $\pu{2 atm}$ pressure. If the tube suddenly bursts, the final temperature of the air will be ($γ_\...
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1answer
86 views

How is the molar weight of C-12 equal to 12 gram ? Why is "g" not considered while calculating molar weight? [closed]

So, I was just pretty confused about how we simply multiply the "mass" of total nucleons in Carbon by the Avogadro Constant, to get the molar "weight" as 12 grams, shouldn't it be ...
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Understanding equivalence point [closed]

I read this passage: “It is important to emphasize that, while a strong acid/strong base titration will have its equivalence point had a pH of seven, the equivalence point does not always occur at pH ...
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Can alkali-doped exohedral fullerene molecules show superconducivity?

Alkali doped fullerenes are one of the few organic materials that show superconductivity. However, when attaching a new molecular system to a fullerene doped with an alkali metal, will it still show ...
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1answer
111 views

Calculating pH of aqueous ammonium hydrogen sulfide solution

I was doing the following question yesterday: Calculate the pH of a $\pu{0.1 M}$ solution of $\ce{NH4HS}$, given $\mathrm{p}K_\mathrm{b}$ of $\ce{NH3}$ is $4.74$, and $\mathrm{p}K_\mathrm{a1}$ and $\...
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Understanding the Osmotic Pressure formula

$$\Pi = iMRT$$ Can this be rewritten as $\Pi = ORT$ where $O =$ osmolarity? The only reason I ask is because my book doesn’t talk about the relationship between osmolarity and molarity, but I came ...
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Are spontaneous exothermic reactions spontaneous due to more stable products or to an increase in the entropy of the surroundings? [closed]

The lattice formation of an ionic compound from its infinitely separated gaseous ions is spontaneous under standard conditions, but I cannot figure out the 'driving force' behind this. One way to look ...
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Dominant factors rendering very low solubility of large aromatic molecules

In terms of structural basis, alkanes are insoluble or immiscible in water because of such presence of C–H...O interactions that are in regime of van der Waals interaction, which tends to be regarded ...
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Is hydrogen peroxide a better oxidizing agent than chlorine gas? [closed]

If we compare the standard reduction potentials of $\ce{H_2O_2}$ with that of $\ce{Cl_2}$: $\ce{H_2O_2 + 2H^+ + 2e^- <=> 2H_2O : E^o = 1.78V}$ $\ce{Cl_2 + 2e^- <=> 2Cl^- : E^o = 1.36V}$ (...
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88 views

Why does CO2 diffuse out of a cylinder in the absence of a pressure difference?

Suppose I have a thermally insulated cylinder containing carbon dioxide (assuming it is ideal) at 1 atm pressure(atmospheric pressure is 1 atm). Now let's consider two cases: CASE-1: I cut open the ...
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1answer
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Definition of dissolve and the state label (aq) in chemical equations

I am confused with the meaning of "(aq)" in chemical equations, and the meaning of "dissolved". What is the actual meaning it is supposed to convey? For instance, in the document &...
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1answer
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What is 'absorbance power' in electrochemistry?

I have been asked $\ce{250 mL}$ solution of unknown molarity of $\ce{CuSO4}$ in water was electrolysed using platinum electrodes. After the passage of a current $2 \times 10^{-3}$ ampere for $19.3$ ...
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1answer
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Does pH gets affected by pressure? [closed]

My attempt- I thought that pH is h+ ion concentration and change in volume will change its equilibrium according to le chatelier's principle . But I want to know is it correct or it needs some ...
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Constraints on pyrotechnic explosives that won't detonate spontaneously at 500 °C when landing on Venus?

The Space Exploration SE question Premature detonation of explosive bolts when landing on hot Venus? explains the need for and widespread use of pyrotechnic fasteners and cable cutters for Mars ...
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1answer
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Finding the rate of a reaction given experimental data for reaction kinetics [closed]

Here is the question: For the reaction: $$\ce{2 A + 2 B → C + D}$$ The following data was obtained from three experiments: \begin{array}{c|ccc}\hline \bf{Experiment} &\textbf{[A] (mol/L)} &\...
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How can the difference between surface energy and electrostatic repulsion be calculated in electroplating?

When metals are electroplated unto surfaces, there are a myriad of forces at play. To set a clear example, if one were to electroplate a magnet with a diamagnetic metal such as bismuth, there will be ...
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Heat released at constant pressure and temperature and heat released at constant density and temperature

Is there a relation between heat released at constant pressure and temperature and heat released at constant density and temperature? I was reading some books on propulsion and combustion, and the ...
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2answers
64 views

Finding freezing temperature and osmotic pressure of an ethylene glycol and glycerol solution in water

A water solution is prepared by mixing $\pu{200 g}$ of a ethylene glycol (ethan-1,2-diol; $\ce{C2H6O2}$) solution (20% by weight) with $\pu{500 g}$ of glycerol (propan-1,2,3-triol; $\ce{C3H8O3}$) ...
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Limitations of Quantum Chemistry [closed]

I have a physics background and I am interested in the applications of quantum mechanics in predicting chemical reactions, and I’m wondering where should I start? I am particularly interested in the ...
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Do the differential expressions of second law of thermodynamics imply a smooth increase in entropy? [closed]

Another statement of second law of thermodynamics can be formulated in terms of system properties and not properties + surroundings (isolated system). For a closed system at constant temperature and ...
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1answer
193 views

What is the n-factor of ferric sulfide when it reacts with oxygen to give ferrous sulfate and sulfur dioxide?

What is the n-factor of $\ce{Fe2S3}$ in this reaction? $$\ce{Fe2S3 + O2 -> FeSO4 + SO2}$$ I broke this reaction down into two parts $$\ce{Fe2S3 -> FeSO4}$$ $$\ce{Fe2S3 -> 3 SO2}$$ And in the ...
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Why is potassium less dense than sodium?

Potassium has a density of $\pu{0.86g/cm3}$ and sodium has a density of $\pu{0.97g/cm3}$,even though potassium is below sodium and one might expect the alkali metals to exhibit monotonously increasing ...
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225 views

Will addition of inert gas change the vapour pressure of a liquid?

From this question on Physics SE Thermodynamics of evaporation: Now imagine the experiment is repeated but instead of vacuum conditions, the water is pressurized with nitrogen at 1 atm. According to ...
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Spin Multiplicities of Ions

The multiplicity is fundamentally defined as $2S + 1$ where $S$ is the total spin. From what I understand, the multiplicity corresponds with the number of unpaired/paired electrons. For example, in ...
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Why does one drain strainer rust while the other does not?

About a month back, I acquired drain strainers for my shower and kitchen sink. The package I got included one of each, which I installed immediately. Within two weeks, the shower strainer was showing ...
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Will a Crooke's Tube stop working after sometime? [closed]

A Crooke's Tube is a cold-cathode tube, wherein electrons are released from the cathode when ionised gas particles strike it with speed. Following a chain reaction, other gas particles also get ...
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3answers
268 views

Rate of a reaction when volume of the system varies with time

Background I was solving this question from this book and I was not able to get any of the options. The gaseous reaction $\ce{n_1 A_{(g)} -> n_2 B_{(g)}}$ is first order with respect to ‘A’. The ...
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2answers
443 views

Is the origin of non-integral atomic masses the difference in masses of the proton and neutron?

Yes, atomic masses are non-integral due to isotopes and binding energy. These are the two reasons I found on google and other answers on stackexchange. But there is something else - isn't the most ...
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In a perfect electrolytic cell, would the anode and cathode change by the same amount

If I had a theoretically perfect electrolytic cell, such as one with Copper anodes and cathodes, and a copper nitrate solution, over a given time period with a voltage applied, would the change in ...
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1answer
730 views

Can the equilbrium constant ever be exactly 1?

According to my book, In the real world [...] it is unlikely that any reaction would have exactly equal concentrations of products and reactants at equilibrium. This was mentioned in context to the ...
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How to graph a second order reaction with two different reactants

In a laser flash photolysis experiment, $\ce{C6H5NH2}$ $(C_0 = \pu{60 \mu M})$ is oxidized to the corresponding radical cation. The disappearance of radical cation is monitored spectrophotometrically ...
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1answer
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Burning of Natural Gas [closed]

I would like to compare the burning of Natural gas to heat the external object 1) when Natural Gas gets fired with Pure Oxygen 2) when Natural gas gets fired with Atmospheric Air. What are the ...

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