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.

Filter by
Sorted by
Tagged with
3
votes
0answers
18 views

Why would T1 relaxation time change ~20 fold between solvents for the same substance?

I have a simple, completely conjugated pyridinium salt with MW of ~300 g/mol. The molecule consists of regular non-labeled atoms (only C, H, N). If the 1H T1 relaxation time for this molecule is ...
0
votes
0answers
28 views

Calculating change in Gibbs Free Energy for a specific type of problem

Can anyone describe what is going on here? $$Si(liq.)=Si_{(1 weight percentFe)}$$ I have come across this statement quite a few times in Metallurgical Thermodynamics.All that they ask for is change in ...
-1
votes
0answers
11 views

How to find K given the pH absorbance [closed]

He runs a strongly basic solution containing the dye (pH ≈ 14.0) and a strongly acidic solution containing the dye (pH ≈ 0.0). He finds that the greatest differences between the two spectra was found ...
-1
votes
0answers
14 views

Chemistry hw Properties of Gases! [closed]

Solve the chart that says (Final description) must include the: factors that are changing, effects on pressure, constants)ty <3
6
votes
5answers
635 views

Why do the units of rate constants change, and what does that physically mean?

Just to be clear, I do understand that the units of the rate constant k is selected to make the equation dimensionally consistent. That is not what I am asking. It should be the case that k 'means' ...
1
vote
0answers
19 views

Effect of transition energy gap and frequency of microwave on appearance of CW EPR spectrum

Consider continuous-wave EPR for species with only one unpaired electron in the following argument. The interaction energy in the presence of external magnetic field of strength B is given by $$E = Bg\...
0
votes
0answers
38 views

How reliable is spectrometry in the determination of the oldest material Startdust?

After reading one of the latest findings by scientists, Stardust was considered the oldest material on earth. However having not much of an experience with chemistry, I was intrigued upon how ...
1
vote
1answer
53 views

Activation energy and degrees of freedom

According to the Arrhenius equation the rate of a reaction increases as at higher temperature a greater percentage of molecules have translational kinetic energy greater than or equal to activation ...
1
vote
1answer
37 views

Why does the pH of a weak acid not increase by 1 when diluted by a factor of 10? [closed]

Strong acid pH increases by one unit when diluted by a factor of 10, but why do weak acids not?
-3
votes
1answer
68 views

Why does the infrared spectrum of HCl only have one peak? [closed]

Suggest one reason why HCl has only one peak? Does this have something to do with fact that peaks (in IR spectroscopy) represent areas of the spectrum where specific bond vibrations occur and ...
-1
votes
0answers
12 views

Caluclating temperature of how much room temperature water is needed [closed]

How to calculate how much room temperature water (23.3°C) will be needed to drop the temperature of warm water from 50°C to 42°C.
1
vote
0answers
38 views

Solubility of gases in water in comparison to their liquefiability

My textbook of physical chemistry says ...The following factors affect the solubilities of gases in liquids: (i) Nature of the gas and solvent: Generally, the gases which can be easily liquefied are ...
1
vote
1answer
81 views

How does one prove Avogadro's law from Gay-Lussac's?

To understand Gay-Lussac's law, Amedeo Avogadro said In equal volumes of air under constant temperature and pressure, there are equal number of atoms (or molecules). Let's take a hydrogen and an ...
-2
votes
0answers
10 views

Which Component is responsible for stability of Ink? [closed]

A sample of red ink (a colloidal suspension) is prepared by mixing eosin dye, egg white,formaldehyde and water. The component which ensures stability of the ink sample is :- Please Provide a ...
-2
votes
0answers
24 views

Effect of temperature in equilibrium constant [closed]

Why the equilibrium constant decreases with increasing temperature in exothermic reaction and increases with increasing temperature in endothermic reaction?
2
votes
1answer
27 views

Photodissociated iodine laser and population inversion

Iodine molecules ($\ce{I2}$) can absorb in the visible region and dissociate into $\ce{2 I^.}$ radicals. One of the I atoms is in ground electronic state $\mathrm{^2P_{3/2}}$ and the other I atom is ...
-3
votes
0answers
14 views

maxwell boltzmann curve change [closed]

i know that when removing the molecules the curve goes down but peaks at the same place. However I dont understand why it is does this. Even though the number of paricles with energy greater than or ...
6
votes
0answers
88 views
+50

Modelling CRISPR/Cas9 binding and cleavage using a generalized Kittel's zipper model

I am thinking about how to model the process of the binding and cleavage of a CRISPR/Cas9+guide-RNA complex to double-stranded DNA. This post describes the four steps at which a CRISPR/Cas9 system ...
-1
votes
0answers
32 views

How does the Maxwell-Boltzmann distribution curve change when the amount of molecules is halved? [closed]

I wonder how the Maxwell-Boltzmann distribution curve change when half the molecules are removed. I have known that energy becomes less compared to the activation energy, but I'm not sure why this ...
-1
votes
0answers
14 views

Measuring vapor pressure with an isoteniscope

I have a question regarding the vapour pressure. We first have the temperature set at 50 degrees celsius and we set the liquid in the tube to be at the same level. Then we decrease the temperature to ...
0
votes
0answers
38 views

What is dispersed fluorescence spectroscopy?

There's quite a few papers mentioning the use of dispersed fluorescence spectroscopy (such as this, or this), but I cannot find any explanation to what dispersed fluorescence spectroscopy is. What ...
1
vote
2answers
72 views

What is difference between density of the equilibrium and vapour density of the mixture

While solving question on calculating degree of dissociation, I came across this question: At 627 degrees Celsius and 1 atm $\ce{SO_3}$ is partially dissociated into $\ce{SO2}$ and $\ce{O2}$ by the ...
-1
votes
2answers
98 views

why do we see characteristic colors of alkali metals in oxidizing flame?

I am a high school student and I am a little confused in a topic, My confusion is that: We know alkali metals and their salts imparts characteristic color in oxidizing flame, for example: Lithium ...
-3
votes
0answers
28 views

Energy is required to heat ice

How much energy is required to heat 9 ice cubes each with a mass of $\pu{44.7 g}$ from $\pu{-26.3 °C}$ to $\pu{-17.0 °C}?$ I used the formula $Q = mc\Delta T.$ $$\pu{-17.0 °C} - (\pu{-26.3 °C}) = \pu{...
4
votes
3answers
107 views

Work done in expanding a gas reversibly and irreversibly

So, my chemistry teacher gave the class following $P_{external}$ versus $Volume$ diagrams for reversible and irreversible expansion of a gas which are as follows. (Reversible expansion) (...
1
vote
0answers
69 views

Nernst equations for the reduction of sulfate(IV) and nitrate(V) anions

Write a Nernst equation $(\pu{25 °C})$ for system: $$\ce{SO3^2- + 3 H2O + 6 e- -> S^2- + 6 OH-}\tag{R1}$$ and system: $$\ce{NO3- + 3 H+ + 2 e- -> HNO2 + H2O}\tag{R2}$$ I am not really sure if ...
0
votes
1answer
54 views

Calculating phosphorescence quantum yield using the given datas'

A molecular excited state has a fluorescence lifetime of 10 nanoseconds and a phosphorescence life time of 10 microseconds. There are no other processes, what's the phosphorescence quantum yield? I ...
2
votes
0answers
24 views

Calculating the solubility for chromium(III) hydroxide using the complex ion constant

Problem $$ \begin{align} \ce{Cr(OH)3(s) &<=> Cr^3+(aq) + 3 OH-(aq)} &\quad K_\mathrm{sp} &= \pu{6.7E-31} \\ \ce{Cr^3+(aq) + 4 OH-(aq) &<=> Cr(OH)4-(aq)} &\quad K_\...
2
votes
1answer
58 views

Entropy change during irreversible process

Entropy change is defined as $\Delta S = \int \frac{\delta Q_{rev}}{T} $, where $Q_{rev}$ is heat transferred through a reversible process. I’m a little confused how this works, so I have a couple of ...
0
votes
0answers
15 views

real meaning of osmotic and turgor pressures

I am a high school student and I am very confused in how we define osmotic pressure? Osmotic pressure is defined as the pressure required to stop the diffusion of solvent into a solution by applying ...
1
vote
1answer
24 views

Definition of enthalpy of vaporization

The amount of heat required to vapourize one mole of a liquid at constant temperature and under standard pressure (1 bar) is called its standard enthalpy of vapourization. The enthalpy of vaporization ...
1
vote
1answer
30 views

Comparison of evaporation rate of liquids

Evaporation: Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. When a molecule near the surface absorbs enough energy to overcome the ...
5
votes
1answer
65 views

Heat of reaction for the decomposition of AgCl means?

Certain sunglasses have small crystals of $\ce{AgCl}$ incorporated into the lenses, on exposure to light of appropriate wavelength produces a grey colour to reduce the glare following the reaction: $$\...
2
votes
2answers
77 views

Why isoelectronic species give similar spectral lines?

In my perspective those species should give similar spectra those which have same energy of different energy levels as the transition would yeild same energy photon But still the answer to this ...
22
votes
4answers
1k views

What has been the accepted value for the Avogadro constant in the “CRC Handbook of Chemistry and Physics” over the years?

Some questions about the constant made me curious as to exactly how much the accepted value has changed over the years. I am pretty sure that I learned a rounded value of $6.023\times10^{23}$ about ...
1
vote
0answers
54 views

Is it true that one atom does not form a molecule? [closed]

Here it states that one atom can form a molecule. Notice here that , one N and one O atoms are related
1
vote
2answers
70 views

How is this possible in mole concept? [closed]

L = $6.022*10^{23}$ If I have one atom of oxygen , it has exactly L value. Now 2 atoms of a oxygen have 2L value.(Note that I mean 2O and not $O_2$here) Well , if we take a molecule made up of 2atoms ...
0
votes
2answers
64 views

What affects the vapor pressure of a pure liquid? [closed]

So pretend we have two samples of pure benezene in equilibrium with its vapor. One sample containing 0.5 mol and one containing 1 mol. They're also both at the same temperature. Let's pretend they're ...
3
votes
0answers
44 views

Does correct bond lengths and angles imply that water is in a potential minimum?

So I come from the math community (so please disregard my ignorance on the topic). If I have a water molecule and write the potential energy surface associated with it, my understanding is that I will ...
8
votes
1answer
193 views

What does this example mean? Slow cooling of 40% Sn alloy from 800°C to 600°C: L → L and γ → L, γ, and ε → L and ε

It's in a phase diagram topic. It's about Cu-Sn phase diagram. And it has a question of: Write the schematic diagram describing the following scenarios and identifies the regions and the phases when ...
3
votes
0answers
70 views

A thermodynamics problem with an interesting equilibrium condition

Usually, when we analyze reactions, we assume that the reaction takes place at constant pressure or at constant volume. But there is no reason to assume this is generally the case, and so my friend ...
5
votes
0answers
19 views

Does π values vary in Hansch-Fujita equations for a given substituent?

I was reading about Hansch-Fujita equations from Hansch-Fujita paramaters and observed that the $π$ values of substituents (analogous to Hammet $σ$ values) change according to the specific environment ...
0
votes
0answers
21 views

Do the ions of the two electrolytes mix in the salt bridge of a galvanic cell? [duplicate]

I read several times in books and on the internet that they do not, but this illustration on the Wikipedia confused me because of the zink and the sulfate ions are written above the arrow (image ...
0
votes
0answers
42 views

A doubt in a problem on electrometallurgy

I do not understand why the number of cathodes has been considered as 30.They give an explanation that each half surface in the two extremes are to be neglected.I do not understand why should one end ...
0
votes
2answers
149 views

What is the essence of chemistry? [closed]

I am an engineering student who loves physics but didn't quite enjoy chemistry. a. When I was in high school chemistry to me was something not as inspiring as physics but in which I couldn't solve ...
2
votes
0answers
36 views

Concentration of sulfur in turbid solution

I recently participated in an experiment where I need to calculated the reaction orders and the reaction constant of the reaction: $$\ce{8 Na2S2O3(aq) + 16 HCl(aq) -> S8(s) + 8 SO2(g) + 16 NaCl(aq) ...
1
vote
1answer
28 views

Phase rule for a pure substance in vapor-liquid region

I'm confused with how the Gibbs Phase Rule works for pure substances in liquid-vapor mixtures. According to the phase rule, there should only be one degree of freedom for a two-phase mixture with a ...
6
votes
1answer
490 views

What is the bond energy of H-O? Wikipedia disagrees with itself

What is the bond energy of H-O? Wikipedia disagrees with itself: On English Wikipedia: 467 kJ/mol On French Wikipedia: 366 kJ/mol What is the right value?
4
votes
1answer
34 views

When to include the mass of the dissolved substance in calorimetry problems?

In some calorimetry problems, in which a substance is dissolved in water and we want the heat of the reaction, the mass of the dissolved substance is included in the mass plugged into mcat but other ...
-1
votes
1answer
26 views

As electron energy increases, does ionisation energy decrease?

"Electrons are negatively charged, therefore, two electrons repel each other. When electrons are paired in a 3p orbital there is electron pair repulsion which causes the energy of the electrons ...

1
2 3 4 5
76