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
-2
votes
1answer
44 views

Is each bag of plastic a polymer/macromolecule? If yes, why does it tear so easily? [duplicate]

For example, polyethene is a macromolecule. So each bag of polyethene should be one molecule. Doesn't tearing it therefore involve breaking strong covalent bonds? Shouldn't the energy needed to do ...
-3
votes
1answer
25 views

The meaning of USFDA (in cosmetics) [closed]

The full meaning of USFDA base on the definition of cosmetic meaning and production
0
votes
1answer
43 views

How is reversible expansion work a state function? [closed]

Work, as we know, is a path function. But between given initial and final states, there can be only be one reversible path. Is this true? If yes, then is reversible expansion work a state function? ...
1
vote
0answers
26 views

How to calculate lower and higher calorific values using standard enthalpies?

Calculate the lower and higher calorific value of benzene, expressed in $\pu{kJ L^-1},$ if the standard enthalpy of formation is known: $$ \begin{array}{lc} \hline \text{Compound} & \Delta_\mathrm{...
-1
votes
1answer
32 views

Why in calculating 25 mM of Tris HCl the answer in gram is automatically refer to the gram in 1000 ml [closed]

In the lab class,my teacher told me that the answer i get in grams is automatically the grams in 1000 ml. Why is it possible without we doing anything the grams i get automatically the grams in 1000 ...
-1
votes
1answer
35 views

Does pressure affect rate constant? [duplicate]

I would like to know if pressure affects rate constant. Suppose pressure affects the rate constant. Does it depend on partial pressure (like: if I add an inert gas to the system), or only increasing ...
-1
votes
1answer
51 views

How much heat is lost to the calorimeter when hot water is mixed with cold? [closed]

If a student adds $\pu{100.00 g}$ of hot water at $\pu{50.00 °C}$ to $\pu{100.00 g}$ of cold water at $\pu{25.00 °C}$ and measures a heat change of $\pu{10707.37 J}$ for the hot water and $\pu{4778.86 ...
1
vote
0answers
31 views

Recycling flow if the chemical process of acetylene and hydrocyanic acid

I'm having some issues trying to solve this problem, because the concentration of inert in the recycling flow that I calculated is bigger that the concentration of the inert that is enterying to the ...
0
votes
0answers
33 views

Why are HOMO and LUMO energies invariant under spin-flip?

Atomic theory says singlet and triplet energies for the same orbital differ because of exchange interaction. However, molecular orbital (MO) theory describes the energy between the HOMO (highest ...
2
votes
0answers
31 views

Changing Variables in Thermodynamics

I have a question about changing variables in the context of thermodynamics, but I suppose this would extend to any set of variables that have defined and nonzero partial derivatives on a given set of ...
0
votes
0answers
11 views

Anionic surfactants sensitivity to hard water

It is known that anionic surfactants can be sensitive to hard water, as well that the sensitivity decreases according to their headgroup, where carboxylates are the most sensitive, followed by ...
1
vote
1answer
44 views

Calculating the electrode potential from thermochemical data (part 2)

This question is in continuation of this question. I am taking an example of $\ce{Cu^2+}$ in aqueous medium. $$\begin{align} \ce{Cu (s) &-> Cu (g)} & \Delta_\text{a}H^\circ &...
1
vote
1answer
71 views

How does the rate equation account for solids and liquids?

The question is long because I wanted to include the whole thought process. Given the hypothetical reaction: $$\ce{ A(s) + B(aq) <=> C(aq) + D(aq)}$$ One would obtain the equilibrium constant: $$...
0
votes
0answers
26 views

How to calculate enthalpy of mixing for non-ideal solutions?

I have conducted a series of experiments where I basically mixed two solutions to form a non-ideal mixture and then I measured the temperature rise/fall (since both positive and negative deviation are ...
-1
votes
1answer
53 views

Polarity of 1,2-dichloroethane [closed]

I don't understand how 1,2-dichloroethane is non-polar. Both the carbons have tetrahedral arrangements of atoms and I think there should be an overall dipole. Kindly explain why isn't there a net ...
2
votes
1answer
71 views

How to identify an error in cut off filter (optical) usage when running spectrophotometry?

In spectrophotometry, often a cut off optical filter is used. With reference to a long-pass filter, which rejects any wavelengths outside a predetermined interval: low transmission in short ...
-1
votes
1answer
45 views

Can use lead(II) oxide instead of lead(IV) oxide in car battery?

Question: If the discharge input equation $\ce{PbO2}$ is replaced by $\ce{PbO}$, will the battery still work? I think the product will not be water anymore but hydrogen gas. I am asking this question ...
-4
votes
1answer
65 views

How does the boiling point of water inside a pressure cooker change with temperature? [closed]

My question is why a pressure cooker would affect the boiling point at all. To my understanding, the boiling point of a substance is defined by 'The temperature at which the vapor pressure of the ...
0
votes
0answers
113 views

Is a/b > 1 mol/L for a and b in the van der Waals equation?

We know that the van der Waals equation for real gases is $$\left(p + \frac{an^2}{V^2}\right)(V-nb) = nRT.$$ Is $a > b$ always in this equation? In my textbook $a > b$ for gases like $\ce{He},$ $...
2
votes
0answers
97 views

Is there any magnetic resonance spectroscopy that based on orbital angular momentum?

The different momenta of electron and nucleus are described by different quantum numbers. (a) l and m$_l$ describe the orbital angular momentum and quantization on its component along an arbitrary ...
0
votes
2answers
77 views

Why does magnesium hydroxide solution solidify after passage of time?

I have been trying to make a suspension of magnesium hydroxide in water. Around 40% magnesium hydroxide w/w. Initially it is fluid, but as time passes, it solidifies. What is causing this?
0
votes
0answers
50 views

Is the heat (or work) of the system always equal and opposite to that of the surroundings?

I know energy must always be conserved by the first law of thermodynamics, but is there ever a scenario in which a system say releases some amount of energy as work, and the surroundings gains equal ...
0
votes
0answers
51 views

Does the 1s orbital have two different phases? [duplicate]

How can the 1s orbital (in H atom for example) interfere both constructively and destructively (to give rise to bonding and antibonding molecular orbitals) with another 1s orbital, if the 1s orbital ...
0
votes
1answer
57 views

Hydrated electrons produced by radiation vs electrons from electrostatic charge: are they equally reactive?

One of the species generated in water or aqueous solutions by the ionizing radiations are free electrons that quickly become "hydrated" or "aqueous electrons" (see for example this ...
0
votes
1answer
103 views

Why is the Gibbs free energy of a reversible reaction not always 0? [duplicate]

From my understanding, reversible proceses are those where the expression: $$\Delta S_\mathrm{total} = \Delta S_\mathrm{system} + \Delta S_\mathrm{surroundings} = 0$$ is true for all for the entire ...
2
votes
0answers
96 views

What is the name of the physical quantity that is given in kJ/g?

The chemical potential $\mu$ of a pure phase corresponds to the Gibbs free energy $G$ divided by the amount of substance $n$: $${G\over n} = \mu,$$ so the units of $\mu$ are $\pu{kJ mol^-1}.$ What do ...
-1
votes
1answer
45 views

Chemical equilibria - Lab practical [closed]

In an experiment to determine the partition coefficient, how would we assure that the system has reached partition equilibrium?
0
votes
1answer
101 views

Can an elementary reaction have zero order?

I am very confused right now about my approach to this question could somebody help me out with this. I reasoned my answer as given below Let's assume if a complex reaction is of zero order. It ...
1
vote
0answers
42 views

Enthalpy/Temperature change in a chemical reaction

I was wondering how exactly absolute temperature change in a chemical reaction could be calculated. For example, consider this reaction: 3H₂+N₂→2NH₃, ΔH=-46kJ/mol (298.15K) Assuming the given reaction ...
3
votes
0answers
48 views

Is dehydration of cobalt(II) chloride hexahydrate dynamic equilibrium?

I know that the dehydration of cobalt(II) chloride hexahydrate is a reversible reaction, is it a dynamic equilibrium? $$ \begin{align} \ce{CoCl2·6H2O &<=> CoCl2·2H2O + 4 H2O}\tag{R1}\\ \ce{...
-1
votes
1answer
26 views

How rate of absorption remains same throughout the process?

While reading surface chemistry, I got Rate of adsorption is high at begining and then decreases till equilibrium is attained . On the other hand , rate of absorption remains same throughout the ...
0
votes
0answers
74 views

The necessary energy required to ionize 1g of potasium in its fundamental state if the ionization energy is given

The energy of ionization of the potassium is $\pu{6.94\cdot 10^{-19} J/atom}.$ Find the necessary energy to ionize $\pu{1 g}$ of potasium that is found on its fundamental state. Attempt. I really ...
1
vote
0answers
46 views

Comparing average radius of subshells for multielectron atoms

I recently came across a question comparing the average radius of subshells. A search on the internet gave the following result for single electron atoms: $$\langle r\rangle_{n,\,l}=\frac{a_0 n^2 \...
0
votes
0answers
36 views

Dry ice sublimation rate in water

As I got some a finger sized of dry ice in water, it started to bubble vigorously as expected and gave off a lot of smoke. But after 3 minutes or so, the rate of sublimation seems to slow down a lot, ...
2
votes
1answer
107 views

How to derive formulas for n factor of different types of reactions?

While studying Redox reaction, I came across this term called n-factor which seems to me as a short-cut trick to do the questions quickly. Since I am preparing for a competitive exam so our chemistry ...
0
votes
0answers
23 views

Vapour pressure and boiling [duplicate]

I have come across two definitions for boiling point: It is the temperature at which a liquid gets vaporised It is the point where vapour pressure = external pressure How are they related? How does ...
0
votes
0answers
39 views

A gaseous mixture contains hydrogen atoms in the 4th excited state and helium ion; spectral lines emitted when all these return to the ground state

A gaseous mixture contains hydrogen atoms in the 4th excited state, $\ce{He^+}$ ions in 3d excited state, and $\ce{Li^{2+}}$ in 2nd excited state. Find the number of distinct spectral lines emitted ...
-2
votes
2answers
26 views

Is the cell in an isothermal titration calorimeter open to the atmosphere? [closed]

I'm just trying to understand how they can model an isochoric process.
2
votes
0answers
42 views

Does a larger bond energy in reactants mean a more exothermic reaction?

In the book "Combustion Physics" for C.K Law, page 42, it is stated that: The parameter that has the next strongest influence on [adiabatic flame temperature] $T_{ad}$ is the $C/H$ ratio of ...
0
votes
0answers
42 views

What determines the coefficient B in the Bell-Evans-Polyani equation?

From the Bell Evans Polanyi principle, $E_a = A + B \Delta H$. How is the $B$ coefficient determined? This is my thinking: For exothermic reactions (where the transition state resembles reactants more ...
0
votes
0answers
29 views

Number of gas molecules in activated state vs normal state

I have a simple bimolecular reaction $$\ce{A + M <=>[k_2][k_1] A^* + M}\tag{1}$$ where $\ce{A}$ is a molecule which collides with another molecule $\ce{M}$. $\ce{A^*}$ is the $\ce{A}$ molecule ...
0
votes
1answer
61 views

How switching values of $R$, $K_p$ and $K_c$ does not alter the value of change in standard Gibbs energy? [duplicate]

$\Delta_\text r G=RT\ln \frac{Q}{K}$ If we switch $K_p$ from $K_c$, accordingly $Q_p$ will change to $Q_c$. Therefore, value of $\Delta_\text r G$ remains the same. $ΔG^\circ=−RT\ln K=ΔH^\circ−TΔS^\...
0
votes
2answers
55 views

Molecular orbitals in an ionic diatomic compound

The wavefunction of a heteronuclear diatomic molecule, after the orbital approximation and the Born-Oppenheimer approximation, is $$\psi = c_A \chi_A \pm c_B \chi_B $$ where $\chi$ are the starting AO ...
1
vote
0answers
71 views

Relation of partial charge with wavefunction

Suppose we have an one electron system. The probability $P$ that electron's position is in some interval $x + dx$ is given by: $$P = \int_x^{x+dx}|Ψ(x)|^2 dx$$ So if we measure $N$ times the electron'...
3
votes
2answers
262 views

Solubility and covalent character [closed]

We have heard many times that this XYZ solute is soluble in this ABC solvent. But what does being soluble in mean in terms of bonding? What makes a compound soluble in some solvent and not in some ...
-2
votes
1answer
54 views

Do different types of MOs have different occupancies?

There was a question in my textbook regarding the number of electrons in a molecular orbital. The maximum number of electrons in a sigma, pi, and delta molecular orbital are respectively? Now, I ...
1
vote
0answers
101 views

Why does sulphur exist in two forms in solid state, monoclinic and rhombic? Why in one favoured over another at a certain temperature and pressure?

Both Rhombic and Monoclinic sulphur consist of $S_8$ molecules packed together. Yet the former is more stable below $114^{\circ}C$ at 1 atm and spontaneously converts to monoclinic sulphur above that ...
11
votes
3answers
750 views

Why is it so difficult to crystallise anything in a glass capillary?

I'm talking about very fine glass capillaries with a diameter under 1 mm. I've found that if I carry out melting point analysis, the material in the capillary doesn't crystallise again. I did wonder ...
-1
votes
2answers
111 views

What is the difference between mole and molar mass?

In my book it says 1 mole of carbon =1gram atom of carbon =12 gram if I see this relation that seems to me that 1 mole is mass of an atom In grams. But molar mass is different and why we use for ...
3
votes
3answers
611 views

Are coke (solid fuel from coal) and charcoal same thing obtained from different sources?

As coke is obtained from destructive distillation of coal, and charcoal from destructive distillation of substance other than coal (like wood and animal bones), are both the same thing, with charcoal ...

1
2
3 4 5
85