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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1answer
91 views

Can precipitation reactions attain equilibrium?

While studying about the characteristics of Chemical Equilibrium, I came across a point in my book which read A chemical equilibrium can be established only if none of the products is allowed to ...
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2answers
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Does the pre-exponential factor (Arrhenius constant) depend on temperature?

I was taught that the the pre-exponential factor $A$ in the Arrhenius equation \eqref{arrhenius} does not increase with temperature. $$k = A\cdot\mathrm \exp\left(-\frac{E_\mathrm a}{RT}\right)\tag1\...
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35 views

How to calculate the i-value of known NaCl solution, if it is isotonic with known solution of glucose?

How do I calculate the value of $i$ for 1.17% solution of $\ce{NaCl}$, if it is isotonic with 7.2% solution of glucose? I actually do not know where to start in this question. is it possible to ...
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1answer
8k views

Why does steel wool catch fire when rubbed with a battery?

I was watching an episode of Man vs Wild where steel wool was rubbed with phone battery. To my surprise, the wool caught fire. What is the reason for this?
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3answers
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Temperature dependence of reaction rates

Is it correct to say that "Increasing the temperature will always increase the rate of any chemical reaction"? Many articles on the internet and textbooks say yes but what about biochemical reactions ...
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1answer
53 views

Why is a TTT diagram called isothermal transformation diagram?

Why are TTT diagrams called isothermal temperature diagram?As far as I know the temperature variation is plotted with the variation of time in a TTT diagram. Then why do we call it "isothermal".What ...
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1answer
1k views

Why does the first lithium stationary state have n = 9/4?

The ionization energy of $\ce{He+}$ is $19.6 \times 10^{-18}~\mathrm{J~atom^{-1}}$. What is the energy of the first stationary state ($n=1$) of $\ce{Li^{2+}}$? Since the question specifically states ...
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1answer
51 views

Calculating bond energy given the enthalpy value of burning reaction

The burning enthalpy (exothermic) of $\ce{NO +O2 ->NO2}$ is $\pu{57 kJ mol^-1}$ and $\ce{O=O}$ bond energy is $\ce{494 kJ mol^{-1}}$, then what is the bond energy of $\ce{N-O}$ ? So I balanced the ...
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2answers
60 views

Finding the pH of the solution

In this video, at 3:30 min professor solves two equations $$\ce{H2O —> H+ + OH-}$$ and $$ \ce{HCl —> H+ + Cl-}$$ and deduces $[\ce{H+}] = [\ce{Cl-}] +[\ce{OH-}]$. How come this happen from ...
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1answer
35 views

How would I find the molarity/concentration of a gas using pV = nRT?

The problem I'm working on is: At $\pu{1100 K}$ and a total pressure of $\pu{1 atm}$, $\ce{SO3}$ is $75.0\%$ dissociated. $$\ce{2SO3(g) <=> 2SO2(g) + O2(g)}$$ Assume $\pu{1.00 mol}$...
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1answer
89 views

How to calculate molecular emission spectra?

Is there free software which can calculate the fluorescence emission spectra of organic molecules? Let's say for example: rubrene There is a bunch of quantum free quantum chemistry software: https://...
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0answers
43 views

Explain why can't zinc be plated out from a Zn(II) solution using standard reduction potentials

I am currently learning about electrochemistry using Zumdahl's Chemistry [1, pp. 709–710]. One of the critical thinking questions is Why can $\ce{Zn}$ not be plated out from an aqueous solution of $...
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1answer
2k views

Relationship between auto-ignition temperature with pressure and fuel

Experimentally it appears that increase in pressure, fuel concentration, and chain length causes AIT to decrease until a minimum where even further increase in these parameters increases the AIT. ...
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11 views

In which order should you prepare a microemulsion?

So I have isoooctane (oil phase) ,CTAB (surfactant) ,1-butanol (cosurfactant) , and an aqueous solution of metal nitrates as the water phase. In which order should i add these components? Or any ...
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2answers
6k views

How many valence electrons does the azide ion have?

We had a test and and we had a question asking the number of valence electrons in an azide ion, $\ce{N3^{-}}$. I find out that the answer is 16 but I could not understand how. I saw the structure. ...
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1answer
68 views

Reaction of sulphur with calcium carbonate

Can sulphur react with calcium carbonate to form sulphur trioxide and calcium carbide, as the energy of 3(S=O) is greater than ((C=O) +2(C-O))? EDIT: i forgot to say that this is in an oxygen-free ...
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16 views

How to calculate the internal energy change on a phase change?

Since, the system is in material equilibrium, dG for the system for the reaction is 0. However, our instructor told us that dA has a value. How is that?
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41 views

Diffusion between phases based on chemical potential

How is the concept of diagram(b) different from that of (e) and (d) from (f)?Someone told me in one of my earlier posts (Why will A atoms diffuse from β phase to α phase and B atoms from α phase to β ...
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Why will A atoms diffuse from β phase to α phase and B atoms from α phase to β phase?

At the initial compositions 1 and 2 of $α$ and $β$ respectively the chemical potentials of A and B atoms in each phase can be found by extrapolation of the tangents to the free energy curves at 1 and ...
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1answer
82 views

What is the reason for phase separation? [closed]

I have seen phase separation as a phenomenon taking place. However I do not understand why this phenomenon occurs as a counter example to the natural laws of diffusion along the concentration gradient....
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37 views

Conditional kinetic equations

From a biological system, I got the following reaction: $$A+B+D\rightarrow C+C_1D$$ ($C_1D$ is a certain complex) However, if at any given time there are no $D$s to react, and only then, instead the ...
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1answer
75 views

How is the 'rate law' and 'order' for the ozone decomposition reaction can be defined?

How is the 'rate law' and 'order' for the following reaction can be defined? $$\ce{2O3 -> 3O2}$$ "The expression that correlates the rate of reaction with concentration of reactants is known as ...
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Why is the y intercept of a G vs X curve treated as chemical potential?

Whenever I am to prove the fact that the $y$ intercept to the $G$ vs $X$ curve is basically my chemical potential, there are two equations that need to be assumed. One is $$G=\mu _{A}X_{A}+\mu _{B}X_{...
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What are the magnetic quantum numbers for the three real p orbitals?

The form of the p orbitals that we are familiar with are the $\mathrm{p}_x$, $\mathrm{p}_y$, and $\mathrm{p}_z$ orbitals: (source: ChemTube 3D) I also know that the p subshells have the quantum ...
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16 views

Catalyzing the breakdown of Si-O bonds

What catalysts can catalyze the breakdown of (Si-O) bond ? Can you mention some books(ebooks or hard cover) or websites that cover a lot of information about (Si-O) bond characteristics? I have ...
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2answers
81 views

Finding EMF of a galvanic cell without standard potentials

For the galvanic cell $$\ce{Ag | AgCl(s), KCl (\pu{0.2 M}) || KBr (\pu{0.001 M}), AgBr(s) | Ag}$$ find the EMF generated given $K_\mathrm{sp}(\ce{AgCl}) = \pu{2.8e-10},$ $K_\mathrm{sp}(\ce{...
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1answer
79 views

Why enthalpy changes in phase transition when there is no change of temperature?

Why there is a change in enthalpy in phase transition? I'm asking because enthalpy depends only on temperature: $$\mathrm dH = C_p\,\mathrm dT,$$ and the change in temperature is $\mathrm dT = 0.$
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Gibbs free energy calculation for redox reaction

I was wondering if it is correct to calculate the Gibbs free energy of reaction at $P = \pu{1 atm}$ and $T = \pu{1100 K}$ using the NIST-JANAF thermochemical tables. For example, for the reaction of ...
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32 views

For a gas having molar mass M, express specific heat at constant pressure in terms of heat capacity ratio

For a gas having molar mass $M$, express specific heat at constant pressure in terms of heat capacity ratio. My attempt: using $ C_p - C_V = R $ and $ \dfrac{C_p}{C_V} = \gamma $ $ C_p = \dfrac{...
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1answer
44 views

Why do we use Ḡ (“G bar”) as a notation for partial molar free energy?

For partial molar entropy there is a bar that is positioned above the $G$ with a subscript I that is sometimes added to the $G~(\bar{G}).$ The bar I read sometimes denote the "partial nature of the $G$...
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Determine the velocity of the O fragment after the dissociation

A $\ce{SO3}$ molecule is radiated with light with a wavelength of $\pu{193 nm}$, which results in photodissociation. $\ce{SO3} + \text{photon}(\lambda=\pu{193nm})\ce{-> SO2 + O}$ It is ...
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1answer
947 views

Does the speed of an ion affect the current that can flow through a solution?

Typically, when a cathode and anode are inserted into a solution that allows current to flow, the ions are moving with a certain kinetic energy. If the ions were to gain kinetic energy (through ...
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1answer
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Calculating bond dissociation enthalpy of F-F bond

$$\ce{N2 + 3 F2 -> 2 NF3} \quad ΔH = \pu{-263 kJ mol-1}$$ The bond dissociation enthalpies of the nitrogen triple bond and nitrogen–flourine bond are $\pu{946 kJ mol-1}$ and $\pu{272 kJ mol-1}....
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What is the equation that describes the variation in concentration of an inhibitor in an heterogeneous catalysis?

I find myself in quite a pinch: I have to sustain a Chemical Physics exam, and I know for a fact that the professor often asks this particular question: Suppose that we have both a reacting species ...
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2answers
71 views

Will mixing hydrogen and oxygen without a spark result in combustion? [duplicate]

I plan to do the electrolysis of dilute sulphuric acid. This will produce hydrogen gas and oxygen gas at the anodes. I do not plan to collect these gases, but to simply let it form and release into ...
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1answer
201 views

Estimation of pressure and kinetic energy density of stellar interior using kinetic theory of gases

In Physical Chemistry we are working a problem that is confusing. We started by calculating the pressure half way to the centre of the sun assuming that the interior consisted of ionized hydrogen ...
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1answer
101 views

Zero-filling Fourier Transform in NMR [duplicate]

I understand zero-filling increases the resolution of an NMR signal in the frequency domain, but I fail to comprehend how. Why do the artifical points appear between the real points in the frequency ...
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1answer
43 views

What is the cause of decrease in volume of gaseous mixture in the following problem? [closed]

I am studying Gaseous State. The problem says: A mixture of gas contains $\ce{N2}$ and $\ce{C2H2}$. $\pu{20 \\mL}$ of this mixture is added to $\pu{70\\mL}$ of $\ce{O2}$ and combustion is allowed to ...
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1answer
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Work done in reversible isothermal expansion

A cylinder fitted with a frictionless piston is filled with $10~\mathrm{mol}$ of gaseous carbon tetrachloride and immersed in a large bath of water maintained at $300~\mathrm{K}$. The volume of the ...
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1answer
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Average or individual molar heat capacity?

In finding enthalpy change $\Delta H$ during adiabatic, reversible expansion of mixture of two ideal gases $n_1$ mol of $\ce{A}$ ($C_{\mathrm{m},v}=\frac{3}{2}R$) and $n_2$ mol of $\ce{B}$ ($C_{\...
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Why boiling can't take place in closed containers

I am being told that boiling can't take place in closed containers. Can someone please explain why this is so.
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Why is the equilibrium constant unitless?

I read that the equilibrium constant is unitless because the molar activities of each of the species are used in the equilibrium expression, not the actual concentrations themselves. I understand that....
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What happens when two galvanic cells are placed in series

I understand how a single galvanic cell works, and the relation of equilibrium and the Nernst equation. But this appears to contradict the higher voltage in a series configuration because it ...
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1answer
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Why does Freundlich adsorption isotherm not have a term for surface area?

Why does Freundlich adsorption isotherm not have a term for surface area? The formula given by Freundlich adsorption isotherm: $$ \frac{x}{m}= k P ^{1/n}$$ Where $x$ is the mass of gas adsorbed ...
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4answers
108 views

Relation between activation energy and rate constant

Consider two types of reaction. One has more activation than other. If we increasing temperature by same amount in both, rate constant of which reaction will increase more? My attempt: as we know ...
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1answer
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Confusion regarding calculating the pH of a salt of weak acid and weak base

I need to calculate the $\mathrm{pH}$ of a salt of weak acid and weak base in an aqueous solution. Method I used for calculation For a salt of weak acid and weak base (assuming complete dissociation ...
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1answer
5k views

In electrolysis, does it make any difference if the electrolyte is an molten, aqueous or dilute aqueous solution?

I'm an IGCSE Chemistry-extended student, and my question is: in electrolysis, does it make any difference if the electrolyte is in a molten, aqueous or dilute aqueous solution form? An example ...
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1answer
263 views

Understanding chemical kinetics

For a chemical reaction $$\ce{2 A + 2 B -> C + D}$$ the order of reaction is one with respect to $\ce{A}$ and one with respect to $\ce{B}$. The initial rate of the reaction is $\pu{4e-2 ...
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How can the equilibrium shift, while Kc remains constant?

Consider the following reversible reaction. $$\ce{Cr2O7^2-(aq) + H2O(l) <=> 2 CrO4^2-(aq) + 2 H+(aq)}$$ What will happen to the position of equilibrium and the value of $K_c$ when more ...
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1answer
33 views

How to explain Gibbs free energy is a pressure-dependent state function?

I'm aware that through deriving Gibbs free energy to infinitesimal changes, we could get the formula: $\mathrm dG = V\,\mathrm dp - S\,\mathrm dT$, giving that Gibbs free energy is pressure-dependent. ...