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 views

how to find the NH3 and NH4 in the water?

I can not keep my fish and I am told my water has many NH3 and NH4 how to find them and seperate them?
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457 views

What can be done to increase the yield of a product in a chemical reaction that has reached equilibrium?

Let's take the following reaction that has reached equilibrium $$\ce{CaCO3 (s) <=> CaO (s) + CO2 (g)}$$ What can be done to increase the yield of calcium oxide ? My initial thought was to ...
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Calculation of equilibrium constant in a gaseous system A ⇌ B + C

I am supposed to determine whether the following two statements are true or false: For the reaction $\ce{A (g) <=> B (g) + C(g)}$, $K_p = \pu{1 atm}$. If we start with equal moles of all ...
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1answer
34 views

Why is molar mass of a substance and atomic mass number usually the same?

I recognize what atomic mass represent and what molar mass represents by why is it that a substances molar mass and it’s atomic mass are usually the same number Ex: chlorine has an atomic mass of 35....
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133 views

How can a neutral atom attract electrons when it's supposed to have zero charge?

A neutral atom is an atom with an equal number of protons and electrons We know the force of attraction between the proton and electron is equal and assuming that: one proton's positive charge ...
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Does the activation energy depend upon the stoichiometric coefficient?

For the decomposition of $\ce{N2O5(g)}$ it is given that $$ \begin{align} \ce{2 N2O5(g) &→ 4 NO2(g) + O2(g)} &\quad\text{activation energy} &= E_\mathrm{a}\\ \ce{N2O5(g) &→ 2 NO2(...
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Who came up with the box and arrow diagrams for electron configurations?

In general chemistry texts, the electron configurations are sometimes shown in boxes with up and down arrows to show the concept of paired spins. My impression for years was that Hund used such ...
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2answers
102 views

How does the equilibrium shift when concentration of reactant and product are increased simulatenously

Before answering my question, take a look at this example $$\ce{2NOCl <=> 2NO + Cl2}$$ Let's suppose I have 2 mol/l $\ce{NOCl}$, 2 mol/l $\ce{NO}$, and 1 mol/l $\ce{Cl2}$ in a closed system. ...
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What would be experienced In a Subatomic World? [on hold]

What if you're in a subatomic world, what would you experience and why?
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76 views

How to calculate the relationship between the pressures of zinc, carbon monoxide, and carbon dioxide based on mole balance?

Zinc oxide is reduced at a constant temperature in a closed reactor using $\ce{ZnO(s)}$ and $\ce{C(s)}$ as the only starting materials. The following reactions are assumed to be at thermodynamic ...
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The intuition behind usage of wt% in K_T? [on hold]

Why are they not taking the percentage of $a_{\ce{AlN}}$ while in the denominator wt% is being taken. My question is why not simply the weight instead of weight percentage and secondly if at all we ...
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Relation ship between differential rate and rate law

Say for a reaction, $$ \ce{aA + bB -> cC + dD}$$ we have rate $k = k[A]^a \times [B]^b$ and by differential rate law we have $$-\frac{d[A]}{a\, \mathrm{d}t} = -\frac{d[B]}{b\, \mathrm{d}t}$$ ...
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Do Electrons Really 'Spin'?

With regard to the 'Electron Spin Number', lots of websites mention that electrons don't really spin and that the electron spin number has nothing to do with any physical spinning. However, my ...
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Electrolytic cell - Potentials

I'm an electronic engineer student and I'm trying to understand the basics of electrolytic cells and practical values' meaning. Based on my figure and electrode potencial values (Vce, Vre and Vwe), ...
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Rate of reaction of copper poweder with nitric acid [on hold]

Why is the reaction of nitric acid with copper powder initially not fast but it becomes rapid after some time? I have no idea on this one. How does copper reduce dilute nitric acid to nitric oxide ...
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1answer
117 views

Finding the isotherm with given minima

Get the temperature of the isotherm for water for which the local minimum is at $\pu{100 Pa}.$ Use the values of $a$ and $b$ of water. My approach In the van der Waals equation, set $$\frac{\...
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18 views

Change in concentration of 1st order reaction [closed]

For the first order reaction $\ce{A → B},$ is the change of concentration of $\ce{A}$ equal to the change of concentration of $\ce{B}$? And would this be different if you have $\ce{A → B + C}\,?$
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How to calculate pH of final solution using volume and pH of initial solutions? [closed]

When two solutions of equal volume with pH 2 and 8 are mixed, what happens to resulting pH ? How to calculate the final pH? I am being too specific this time.
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1answer
112 views

Equation for the equilibrium constant for the hydration of carbonyls using UV spectroscopy

I was looking through the literature when I found this source: https://pubs.rsc.org/En/content/articlepdf/1967/tf/tf9676302131 Which states that the equilibrium constant Khyd is: Khyd = $\frac{[...
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28 views

Numerical simulation and calculations of pH

a. Reaction of $\ce{CO2}$ addition in water is as follows: $\ce{CO2}$ + $\ce{H2O}$ $\ce{->}$ $\ce{H2CO3}$ b. Then, pH of $\ce{H2CO3}$ solution is increased to 12 by addition of 1M $\ce{NaOH}$. ...
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Spectroscopy and Chromatography [closed]

25 cm^3 of an unknown solution has an absorbance of 0.3. Added is 5 cm^3 of a solution of the same compound (concentration = 10 ppm) and absorbance is now 0.34. Calculate the original unknown ...
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25 views

Measuring change in concentration of hydrogen peroxide

I am conducting an experiment to find the rate constant of the decomposition of hydrogen peroxide, $\ce{H2O2}.$ For this, I was planning on using the integrated rate law: $$\ln(\text{final ...
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1answer
195 views

Equation to find specific gravity (or density) from a solution of sugar and water

Is there an equation or simple way to calculate the final density of a solution made from x grams of sugar and y liters of water? And would it work in reverse? if we have y liters of water at z ...
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1answer
40 views

Is the rate of electrolysis the same throughout as long as voltage is same

In an electrolytic cell, where the electrolysis of dilute sulfuric acid is taking place, would the rate of electrolysis be constant always, even at the beginning? By rate of electrolysis, I mean the ...
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2answers
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Why does a NOx container get cold when NOx is released? and What is the relationship of the vapor pressure curve with the liquid-vapor dome?

The temperature at which $\ce{NO_x}$ is in equilibrium with its liquid and vapor phase at 1 atm is about –84 °C. Does that mean $\ce{NO_x}$ exists as a liquid at that temperature? What about it's ...
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19k views

How to calculate the probability of finding an electron in a box between 0.25L and 0.75L?

If the wavefunction of the electron in a box of length $L$ is $$\psi{(x)}=\sqrt{\frac{2}{L}}\cdot\sin{\frac{n\pi x}{L}}$$ What would be the probability of finding the electron between $0.25L$ and $0....
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44 views

Calculating ionic strength and pH of a buffer solution [closed]

Im trying to calculate ion strength and pH of solution. Components of the solution: 47 ul of 1000 pmol DNA in Elution Buffer (10 mM Tris-HCl pH 8.5) was bound to 3 ul of 10 µM YoYo1 (flourescent dye) ...
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27 views

Two methods for calculating ΔH yield different results [closed]

A problem in my book says: $\pu{140 g}$ of $\ce{N2}$ (perfect gas) changes from $\pu{200 K}$ to $\pu{400 K}$ at constant volume. Calculate the change in internal energy $\Delta E$ and the change in ...
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9 views

Lattice Energy of MX2 type

While finding the solution to the question that which among BaO and BaCl2 has hi that is energy I found that it was BaO whose lattice energy is high and there were explaining it just with charges. So ...
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237 views

Is the equation dG = Vdp − SdT valid only for a reversible process? Can it be applied for an irreversible one too?

In the derivation, we write: $$ \begin{align} G &= H - TS &\quad&\to&\quad \mathrm dG &= \mathrm dH - T\,\mathrm dS - S\,\mathrm dT \\ H &= U + pV &\quad&\to&\quad ...
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744 views

Is the E in Arrhenius equation the change of enthalpy?

I'd like to know whether the activation energy in Arrhenius equation is the enthalpy difference between the transition state and the reactant. If it's not enthalpy, is it Gibbs energy or something ...
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1answer
67 views

Which solvent is good for using SU-8 particle in Optical tweezers?

I'm studying Optical tweezers. I've used Polystyrene for samples. Nowadays, I've got SU-8 pillar. I wanna use that for sample, but its density is heavier than water. I can't use that. So I wanna know ...
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89 views

What is the origin of the Quadratic factor in calculation of XRD peaks?

Whenever we are to calculate the d-spacing(for cubic system) in XRD peaks with reference to Quadratic Factors we do that with the help of the formula $$\frac{1}{d_{hkl}^2}=\frac{h^2+k^2+l^2}{a^2}.$$ ...
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1answer
36 views

Is the density of solute same as the density of solution? [closed]

This problem came up while solving some problems on mass percentage and mole concept. Essentially, our teacher said that the $w/w\%$ and the $v/v\%$ for a given solution will be the same, because in ...
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1answer
2k views

Thermal decomposition of calcium carbonate

Thermal decomposition of calcium carbonate. In general, we heat $\ce{CaCO3}$ to temperature of approximately 825°C it decomposes into calcium oxide and liberates carbon dioxide gas:* $$\ce{CaCO3} \...
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However what is so acidic about CaO and basic(no pun intended) about SiO2 while calculating basicity of slag?

I have seen Basicity to be calculated as $\mathrm{B} = wt\%\:\ce{CaO}/wt\%\:\ce{SiO2}$ particularly in slag bascity/acidity calcuations. Now I do not think that $\ce{CaO}$ is the most basic oxide that ...
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1answer
47 views

Strength of bases and acids

Is it possible that strong acids like H2SO4 behave as weaker ones like CH3COOH when the concentration is really high and vice versa for weak acid? And same question for bases. By this I am generally ...
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337 views

How do I solve such questions on paramagnetism and ferromagnetism?

Match the type of magnetism given in Group I with the material given in Group II: $$ \begin{array}{ll|ll} \hline & \textbf{Group I} & & \textbf{Group II} \\ \hline \text{P} & \...
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Fick's second law atomic diffusion question [closed]

I have a question about diffusion and i'm not sure how to tackle it. A new processing method is being tried for a lithium battery cathode material -LiCoO2. the process leaves the ceramic oxygen ...
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1answer
786 views

In a mass spectrum, how can the sum of relative abundances be greater than 100?

I apologise if this seems a very simple question, and also if I am overlooking something that is very simple. For part of my A Level course, we have to be able to interpret mass spectrometer readings ...
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1answer
39 views

How to prove it mathematically that either rhombic or the monoclinic sulfur is denser?

For the transition, rhombic sulfur → monoclinic sulfur, the value of $ΔS$ is positive. The transition temperature increases with increase in pressure. Which is denser, the rhombic or the monoclinic ...
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Why is there minus sign on dP/dt when deriving the equation for effusion? [on hold]

I just want to the reason behind minus sign on dP/dt. I'm able to workout the rest of the derivation.
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Finding initial mole fraction of ammonia in ammonia-hydrazine mixture using thermodynamic parameters before and after thermal decomposition

A mixture of $\ce{NH3}$ and $\ce{N2H4}$ is placed in a sealed container at $\pu{300 K}$. The pressure within the the container is $\pu{0.6 atm}$. The container is heated to $\pu{1000 K}$ where the ...
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40 views

Rate law for breakdown of ozone to oxygen

For the following problem: Example 3: Write the rate law for $\ce{2 O3 -> 3 O2}$ given that the f‌irst step is fast and reversible, and the second step is slow. $$ \begin{align} &\text{...
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1answer
164 views

How do I make a 0.5 M citrate buffer at pH 4.5?

I need to make a citrate-sodium citrate buffer at 0.5 M concentration and pH 4.5. I calculated the molarities of the citrate and disodium citrate based on the Henderson Hasselbalch equation, using a p�...
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3answers
85 views

$K_c$ vs $K$ in equilibrium reactions

I don’t understand why the following question The decomposition of nitrosyl bromide $(\ce{NOBr})$ proceeds by the following reaction: $$\ce{2 NOBr(g) <=> 2 NO(g) + Br2(g)} \qquad K = 0....
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1answer
54 views

Relationship between Gibbs free energy and potential energy (related to reaction coordinate diagrams)

For a rate law, the rate constant $k$ is given by the equation $$\ln k = \ln A - \frac{E_\mathrm{a}}{RT}\tag{1}$$ If $k_\mathrm{fwd}$ is the forward rate constant and $k_\mathrm{rev}$ is the reverse ...
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1answer
55 views

Is the cathode and anode on the cell notation of an Electrolytic cell on the same side as if how you will write it for a Galvanic cell?

I was reading an online material then I came upon a cell notation for an electrolytic cell (I determined that it was an electrolytic cell because of the absence of a salt bridge). Usually, I will ...
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22 views

How can I calculate for the theoritical potential needed to precipitate a metal in an electrolytic cell?

We were given a problem where we are to calculate the theoretical potential needed to initiate the deposition of $\ce{Cu^2+}$ in a solution buffered to $\mathrm{pH} = 4.00$ and the IR drop associated ...
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How are standard enthalpy of formation values determined?

How are standard enthalpy values of formation determined? And how do you determine other enthalpies, such as the enthalpy of hydration? I'm really confused as to where they got their numbers from.