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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3
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2answers
59 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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0answers
6 views

pH of water when NaHCO3 is added [on hold]

I'm having 1000 L of water whose pH is 5.15 and I'm also having NaHCO3 (pH is 9). How much NaHCO3 in (grams or kilograms) should I add to water make the pH in the range of 8? Please provide me with ...
1
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1answer
58 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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0answers
19 views

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 ...
0
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0answers
13 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{...
0
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0answers
23 views

Writing the formation enthalpy of ammonium

Is it correct to write the equation for the formation enthalpy of $\ce{NH4+}$ as follows $$\ce{NH3(g) + H+(g) -> NH4+(g)}$$ or should it be $$\ce{1/2 N2(g) + 2 H2(g) -> NH4+(g)}$$
4
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0answers
29 views

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 ...
2
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1answer
34 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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1answer
34 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 ...
0
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1answer
23 views

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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2answers
58 views

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

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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0answers
7 views

Query in chemical kinetics in multiple reactions [closed]

A chemical substance A undergoes a chemical reaction and gets converted to another substance B. ​Then B undergoes another reaction and gets converted to a substance C. At the beginning of the reaction,...
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0answers
11 views

Heterogenous Mixture [closed]

1.Gas(Solvent)-Gas(Solute) 2.Gas(Solvent)-Liquid(Solute) 3.Gas(Solvent)-Solid(Solute) 4.Liquid(Solvent)-Gas(Solute) 5.Liquid(Solvent)-Liquid(Solute) 6.Liquid(Solvent)-Solid(Solute) 7.Solid(Solvent)-...
6
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1answer
88 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 ...
0
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1answer
39 views

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

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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2answers
56 views

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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0answers
22 views

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 ...
3
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2answers
174 views

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....
2
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1answer
29 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. ...
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0answers
32 views

Arrhenius equation using concentration

I've been conducting some experiments to determine the temperature dependence of a reaction. To do this, I've been conducting the experiments at different temperatures and generated a graph of $\ln{[\...
2
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1answer
32 views

Is there any book where specific heat capacities are given?

I want to find the value of the specific heat capacity of aluminium nitrate nonahydrate, in order to calculate mixing effects in a chemical reaction. I am looking for a source, such as a book or link ...
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0answers
48 views

Are there any gases that can not be turned into liquid, or liquids that can not be frozen solid?

My son points out that some solids can not be melted (because they combust, for example). He wonders if there are any liquids that can not be frozen, or gases that can not be liquified.
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46 views

Enthalpy of an ideal gas undergoing change in pressure and temperature

A 1.50 mol sample of an ideal gas at 245 K and 0.75 bar pressure is altered by some process that takes it to a state in which its temperature is increased to 295 K and its pressure is increased to 0....
2
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1answer
34 views

Conductance of the mixture of two solutions with given resistance values [duplicate]

If $R_1$ and $R_2$ are the resistances of two solutions of equal volume what is the conductance of the mixture in the same conductivity cell? In general, I grasped neither the approach, nor the ...
2
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0answers
47 views

How to calculate the value of heat absorption/ heat release during water electrolysis?

The overall reactions with the enthalpies of water electrolysis at room temperature can be represented by the equation below: $$\ce{2H2O + \pu{237.2 kJ mol-1} + \pu{48.6 kJ mol-1} → 2 H2 + O2}$$ ...
4
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2answers
77 views

Exothermic: enthalpy or heat?

I am used to thinking of exothermic reactions as being defined as having negative $ΔH.$ However, I also am used to hearing/thinking of exothermic reactions as "releasing heat". Since change in ...
6
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1answer
53 views

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 ...
5
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1answer
52 views

What drives vibrational cooling in an excited stated?

As we excite a molecule from its ground state, $S_{0,v=0}$, to some excited state in a higher vibrational state, i.e. $S_{1,v'=3}$, what drives vibrational cooling within that excited state manifold (...
5
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3answers
101 views

Why doesn't beryllium, an elemental solid, obey Dulong and Petit's law?

Beryllium has a molar heat capacity of $\pu{17.7 J mol-1 K-1},$ which is quite far from the $\pu{25 J mol-1 K-1}$ as predicted by Dulong and Petit's law. What is the reason for this discrepancy?
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29 views

Calculate change in entropy when both temperature and volume change

Calculate the change in entropy when $\pu{23.5 g}$ of oxygen gas is heated from $\pu{240 K}$ to $\pu{360 K}$ in such a way that its pressure increases from $\pu{2.00 kPa}$ to $\pu{8.00 kPa}.$ Assume ...
3
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2answers
108 views

Why is there a z² label for d orbitals, but no x² and y² labels with corresponding shapes?

I know that the $\mathrm{d}_{z^2}$ orbitals are named as a result from the conversion of the angular component of the hydrogen-like wave function in terms of Cartesian coordinates, but how come we ...
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0answers
15 views

Is Sodium Lauryl Sulfate considered a Sodium salt of sulfated oleic acid

Sodium Lauryl sulfate (SLS) is synthesized from palm oil which is high in oleic acid. Is SLS considered a sodium salt of sulfated oleic acid? I am asking this in order to make sense of some Federal ...
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0answers
16 views

Changing conditions of gaseous mixture

A gaseous mixture of $\ce{NO2}$ and $\ce{N2O4}$ is sealed in 4 identical vessels with movable pistons. When the conditions are modified as described in 1) to 4), in which condition does the molar ...
0
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4answers
96 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 ...
0
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1answer
51 views

Entropy change in non-ideal solutions

We know that some solutions show positive deviations and some show negative deviation from Raoult's law.The former is endothermic and the latter is exothermic. And again, the volume change show ...
0
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0answers
70 views

Which of the following statements is true if HI is formed in the following reaction?

Which of the following statements is true if HI is formed in the following reaction? $$\ce{H2(g) + I2(g) -> 2HI(g)}$$ a. There are no collisions between the reactants in the reaction. ...
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1answer
35 views

Why electrons move to Cu in galvanic cells?

I'm student who learning about chemistry, and I got problem about understanding why electorns move to Cu in galvanic cells. Let's think the reason for electrons going to Cu is that the standard ...
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0answers
29 views

Reaction between copper and silver(I) nitrate in aqueous medium

What is the reaction between $\ce{Cu}$ and $\ce{AgNO3}$ taking place in aqueous medium? The answer given was: "Only" oxidation of $\ce{Cu}.$ My concern is: how is only oxidation of $\ce{Cu}$ ...
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1answer
48 views

What does it mean for chemical reaction network to be in equilibrium?

What does being in "equilibrium" mean for a set of chemical reactions? If we have some number $n$ of $\ce{A}$ molecules and $m$ of $\ce{B},$ and the following reaction where $\ce{A}$ and $\ce{B}$ can ...
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1answer
30 views

Decrease in molar conductivity with increase in concentration

Why does molar conductivity $Λ$ for strong electrolytes decrease with increase in concentration? I mean, more concentration would mean higher number of solute particles present in the solution, and as ...
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0answers
24 views

How do you remove lumps in reagents without contaminating them?

I think desiccating the powdered reagent would help remove lumps (at least in preventing lump neoformation) but would desiccation alone collapse all lumps in a powder (say KCl as it lumps easily), or ...
10
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2answers
348 views

Kolmogorov backward equations in active biological systems

I am trying to understand the following equations from a paper by Wang et al. [1, p. 5 at the SI]: Michaelis–Menten Representation of the Kinesin Cycle We assumed that there is a strong ...
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0answers
24 views

Is there any formula for finding out probable distance of orbitals or do I just remember the values? [closed]

Like, do I need to just remember that it is less in 3d than 3s and so on?
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1answer
20 views

Dosing leaves with Zinc Nitrate for pollution experiment - Need specific concentration

I am trying to assess the pollution tolerance of an insect using Zn as a proxy. I have a supply of Zinc Nitrate Hexahydrate that I want to use to contaminate dried leaves (the insect's food). The LD50 ...
1
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1answer
29 views

What molecules are produced in carbon arc lamp and how do they produce light?

I am curious about the chemistry of the arc lamp (an indirectly for the incandescent bulbs) thus I would like to ask the following. It is a common understanding that the electrons pushed inside an ...
1
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0answers
60 views

A tricky question in Eudiometry/Gas analysis

In a eudiometer $\pu{14 ml}$ of $\ce{CH4}$ and $\pu{38.5 ml}$ of $\ce{O2}$ was introduced. After explosion and cooling to initial temperature ($\pu{23°C}$) the volume of eudiometer was found to be $\...
0
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2answers
37 views

What is the physical meaning of fractional oxidation numbers of elements in compound

Many times I encounter oxidation numbers like -1 in the peroxide for oxygen, -1/2 in superoxide, and in some other compounds some elements have 8/3 or such like that...what is the physical meaning of ...
8
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1answer
1k views

What does “lit.” mean in boiling point or melting point specification?

For example, this Xanthene 99% specification from Sigma Aldrich states: \begin{array} \\\hline \text{bp} & 310-312 ~^\circ\mathrm{C~ (lit.)} \\\hline \text{mp} & 101-102 ~^\circ\mathrm{C~ (...
6
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1answer
82 views

Equilibrium constant for a solid-solid equilibrium

Suppose there are two equations: $$ \begin{align} \ce{A(s) &<=> B(g) + C(s)} &\quad &K_1 \tag{R1}\\ \ce{B(g) &<=> D(s) + E(s)} &\quad &K_2 \tag{R2} \end{align}$$ ...
1
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1answer
51 views

Steady State Approximation final integral proof $\frac{d[P]}{d t}=k_{a}[A]$ yielding $[P]=\left(1-e^{-k_{a} t}\right)[A]_{0}$

I want to ask a question about the Steady State Approximation integral. I understand the steady state integral works in Leyman's terms as the intermediate is formed as fast as it is consumed so the ...