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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
15 views

If water freezes at 32 °F (0 °C) at sea level, then what temperature does ice melt?

If water freezes at 32 °F, what happens to that newly formed ice at that temperature? Does it start melting as soon as it’s frozen, or does it require more heat to melt again? If it does require more ...
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1answer
22 views

Why does snow sublime even when the surrounding temperature is below 0 °C?

Snow in winter below 0 °C, still sublimed very slowly over time. If I’m not mistaken, sublimation is an endothermic process. Where is this absorbed energy coming from when the surrounding temperature ...
2
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3answers
69 views

Effect of dilution on the degree of dissociation of an electrolyte

My book says that on dilution, the degree of dissociation of an electrolyte increases. Consider the reaction: $$\ce{A(aq) <=> C(aq) + D(aq)}$$ Let $\ce{A}$ be the electrolyte that splits into ...
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0answers
303 views
+50

Single-molecule magnet with electrically-controlled permeability: How does the Titan Shield from Deus Ex work?

In a recent installment of Deus Ex game series there is an augmentation called "Titan Shield" (it has nothing to do with $\ce{Ti}$ element): A neodymium skin underlay matrix built of nano-meshed ...
-4
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1answer
17 views

Problem from Ionic Equilibrium [duplicate]

This seems to be a pretty easy problem but I cannot understand why we do not consider the contribution of $\ce{H+}$ ions by water (water dissociates into $\ce{H+}$ and $\ce{OH-}$) and only that of $\...
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0answers
22 views

How does changing parameters in orientation factor equation affect K?

I am bit confused about orientation factor. According to equation $$K = pz_0\mathrm e^{-E_\mathrm{a}/RT}$$ $K$ is equilibrium constant, $p$ is collision orientation, $z$ is collision frequency and $...
8
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2answers
680 views

What is the difference between chemical equilibrium and dynamic equilibrium?

Is chemical equilibrium and dynamic equilibrium the same thing? Both point to the reversible reactions and no net changes in the concentrations of product and reactant. Dynamic equilibrium from ...
1
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1answer
27 views

Why does eutectic point has three phases, but consolute point has two phases?

At eutectic point, there are three phases: solid A, solid B and homogenous liquid phase containing both A and B. But at consolute point, we are told it has 2 phases: liquid A and liquid B. Why isn'...
5
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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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1answer
69 views

Why could it be assumed that the standard enthalpy change is independent of temperature down to 25 °C?

For the reversible reaction of pyruvic acid to 2,2-dihydroxypropanoic acid, we calculated enthalpy using NMR and extrapolated from area (integration) and peaks etc. We then plotted $\ln K$ vs $1/T.$ ...
3
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1answer
101 views

Are these numbers Madelung constants?

I have no idea of chemistry, just a little bit what I know from school, but I found through some search some connection between entropy (Shannon entropy) of the divisors of some natural numbers and ...
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2answers
53 views

Hess's Law and ΔH

Target equation: $\ce{Mg(s) + 1/2 O2 -> MgO(s)}$ $$ \begin{align} \ce{MgO(s) + 2 HCl(aq) &-> MgCl2(aq) + H2O(l)} &\quad ΔH &= \pu{-1300 kJ} \tag{1}\\ \ce{Mg(s) + 2 HCl(aq) &-&...
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3answers
42k views

Effect of impurities on melting point

This is a 10th-grade question. The melting point of a substance decreases with increase in presence of impurities in it. The melting point of ice decreases from 0 °C to -22 °C on mixing salt in it ...
3
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1answer
23 views

Is it possible to calculate the 'overall' redox potential of a system?

For a solution where many redox reactions occur (e.g. cytosol, soil solution), can we consider anything as 'overall' redox potential of a system? Is there a formula to quantify it in relation to the ...
2
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3answers
92 views

Are viscoelastic materials to be considered solids or fluids?

I recently stumbled upon the concept of viscoelasticity. Not being a chemist, but being interested in the topic, I started to read the wikipedia article. The main thing I extracted from it is: ...
7
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1answer
12k views

How do I distinguish between internal energy and enthalpy?

I am finding it hard to distinguish between the two. Can someone explain the two terms and the difference between them? I tried learning from Wikipedia, but it said for both the above terms that it ...
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1answer
27 views

How is molefraction of a solution different in vapour state vs in solution vs vapour-liquid equilibrium?

I have this question we are given 'x' grams of benzene and 'y' grams of toulene, it is said that the vapour pressure of benzene is 75mmHG and that of toulene is 22mmHG and we are supposed to find mole ...
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1answer
2k views

A thermos bottle containing milk is shaken vigorously

I have a conceptual physical chemistry question here. A thermos bottle containing milk is shaken vigorously. Consider the milk as the system. Will the temperature rise as a result of the shaking? ...
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1answer
40 views

What is the relationship between enthalpy of atomisation and enthalpy of sublimation?

We know that we have to first break the metallic lattice to turn the metal into a gas and hence there should be some sort of relation between the two. I am trying to answer this question: The $E^θ(...
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0answers
26 views

Can an electron of a atom of restricted to 2nd shell be excited to third shell? [on hold]

If there is an electron in the 2nd shell in the s subshell, can it get excited to the 3rd shell or is it only limited to the p subshell? Like hydrogen has only the 1st shell but I've seen many ...
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2answers
89 views

How can I find the Van der Waals constants (a and b) without any critical values?

I'm given a container of gas that is kept at constant temperature, and whose volume is decreased by applying pressure, from A to E, as the graph shows. I am given the temperature, the total moles in ...
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0answers
21 views

What is the formula for vapor pressure of liquid related to surface tension of liquid?

What is the formula for vapor pressure of liquid related to surface tension of liquid? I know that if the surface tension increases, vapor pressure will decrease. Toluene evaporates faster than ...
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1answer
47 views

Calculating pressure [closed]

Calculate the pressure in Pa of a 760mm column of mercury when the density of Hg is 13.5951g/cm^3 at room temperature. P= dgh P=(0.0135951kg/cm^3)(9.81m/s^2)(0.76m) P=0.101 Where did I go wrong? ...
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0answers
22 views

Can a system be designed which equates reaction rates of endothermic reactions using a single power source? [closed]

My goal is to use a single source of heat in an experiment with 2 separate endothermic reactions. My hypothesis is that by conducting this experiment under water, the reaction time of both of the ...
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1answer
46 views

Why is the rate of effusion of a gas inversely proportional to (absolute) temperature? [duplicate]

(iv) Rate of effusion of a gas: The rate of passing of a gas through an orifice may be given as: $$r = \frac{PA}{\sqrt{2\pi RTm}}$$ where $P = $ Partial pressure of the gas $A = $ Area ...
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3answers
2k views

Why does radiocarbon dating only work in nonliving creatures? [duplicate]

I understand how carbon dating works, though I do not understand why it doesn't happen while a creature is living. Because while we are alive we still have carbon 14 in us, so shouldn't it work?
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0answers
20 views

Order of reaction in adsorption process

(1) $\ce{PH3(g) <=>[W]PH3(adsorption)->[W]P(s) + 3/2 H2(g)}$ The decomposition of phosphine on tungsten surface at low pressure is a pseudo first order reaction. This is because the rate of ...
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0answers
29 views

Need a container filled with gas phase anions (negatively charged gas molecules/particles) for an experiment [closed]

Does this even exist? How could I get it? Could I make it? I know that most gas molecules/particles have an overall neutral charge. But I need gas phase molecules with an overall negative charge (i.e ...
-1
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1answer
85 views

What happens when Ar and HCl are mixed at 77 K? [closed]

So our teacher asked us a simple question in the classroom: What happens when Ar and HCl are mixed at 77 K? and no other information was given. We replied various possible answers for that such ...
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1answer
37 views

Order of reaction for hydrogen ions being ignored

I have been reading through a case study about calculating the order of reaction for the following reaction: $$\ce{H2O2 + 3 I- + 2 H+ -> I3- + 2 H2O}$$ The paper uses an iodine clock reaction ...
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0answers
19 views

Application of general binding equation in ITC experiment [closed]

A hypothetical protein $(\ce{M})$ binds a ligand $(\ce{X})$ with $1:1$ stoichiometry, a dissociation constant, $K_\mathrm{D} = \pu{1 μM},$ and binding enthalpy $ΔH = \pu{-5 kcal/mol}.$ Suppose an ITC ...
2
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1answer
71 views

How to calculate the number of protons in a sphere given the volume and the pH?

The spherical radius of a nano-droplet of a solution ($\mathrm{pH}$ of which is $6$) is given as $\pu{20nm}$. I can find the molar concentration of $\ce{H+}$ and subsequently the number of $\ce{H+}$ ...
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0answers
16 views

Interpretting relative probabilities based on Boltzmann's probability distribution?

I understand that Boltzmann's probability distribution gives the relative probability of one microscopic state in comparison to the other (P1/P2) but I don't know how exactly to understand this. For ...
-1
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1answer
18 views

Chemical equilibrium [duplicate]

When calculating equilibrium constant with partial pressures if there is a solid involved should we consider it in the total number of moles in mole fraction?
3
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2answers
60 views

Giving too much energy to an exothermic reaction [closed]

What will happen in an exothermic reaction if more than required energy is given? I mean, will it produce even more energy which will be highly dangerous or nothing will happen according to Le ...
1
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1answer
170 views

Enthalpy change of gas expansion against constant external pressure

A certain mass of gas is expanded from $\pu{1 L}$ at $\pu{10 atm}$ to $\pu{4L}$ at $\pu{5 atm}$ against a constant external pressure of $\pu{1 atm}$. If initial temperature of gas is $\pu{300 K}$ and ...
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5answers
9k views

Evidence of orbitals?

How do we know that there are different types of orbitals? For example, what evidence is there for the existence of $\mathrm{p}$ orbitals instead of there being multiple $\mathrm{s}$ orbitals (for ...
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0answers
43 views

Validity of Maxwell-Boltzmann distribution for solids [duplicate]

Suppose there is a solid made of avogadro number of, say, aluminium atoms. This solid is kept at 273 K. According to Maxwell-Boltzmann distribution, all the particles or atoms will not have the same ...
0
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1answer
52 views

Why does an electron lose energy so that it falls back to a lower energy state than just stay at the higher energy state?

Suppose an electron in the 2nd shell gets excited and jumps to the 4th shell. Shouldn't the electron then exist in an unstable equilibrium in the 4th shell, than lose energy and drop down to the 2nd ...
1
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1answer
38 views

What is a material more easily cut than shattered? [closed]

I'm currently developing a sci-fi concept for animation which partially involves a typical "the earth has been overrun by XYZ" scenario. One of the ideas for XYZ we're thinking of is a species of ...
18
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6answers
4k views

Does the Maxwell-Boltzmann distribution apply to gases only?

The Maxwell-Boltzmann distribution can be used to determine the fraction of particles with sufficient energy to react. I know that the curve applies to gaseous reactants and would like to know whether ...
0
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1answer
9k views

Equation to calculate the triple point

Is there any equation that can calculate the triple point of a substance? Because a method for calculating the critical temperature and the Boyle temperature of a substance that I posted in another ...
4
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1answer
65 views

What is the electrochemical reaction of this battery?

I've watched a YouTube video "Soda Can Battery - Power From Trash - DIY Project" by Source Port Services. I understand that the anode can be oxidised, but what is the reduction reaction at the cathode?...
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1answer
53 views

Decomposition of total Interaction energy with SAPT or EDA-NOCV

I want to perform energy decomposition analysis for some Hydrogen bonded complexes. I came to know that ORCA and Psi4 allows EDA-NOCV an SAPT(0,2,3) respectively. But I do not know which one would be ...
3
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1answer
397 views

Properties of azeotropes

Consider two liquids with vapour pressures in pure form being ${P^o}_A$ and ${P^o}_B$. ${P^o}_B >{P^o}_A$ which implies liquid B is more volatile. If the liquids formed an ideal solution, then a ...
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1answer
190 views

Reaction with tin(IV) iodide and hydrogen peroxide [closed]

Today I reacted tin(IV) iodide $\ce{SnI4}$ (dissolved in water) with hydrogen peroxide. This produced a yellow/brown colour (I'm guessing due to formation of $\ce{I2}?).$ I then added some petroleum ...
10
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3answers
3k views

Why weren't the electrons attracted to doubly charged Helium particles in the Rutherford experiment?

I have a chapter and in it there was a topic on the Rutherford experiment. It is written that doubly charged helium particles or alpha particles were thrown towards a very thin gold foil and some of ...
2
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2answers
81 views

Why when deriving the Clapeyron equation can you assume that dH = dq, as surely the pressure is not constant?

Part of the Clapeyron equation involves replacing $\Delta S$ with $\Delta H/T$. I can see the step from $\Delta S$ to $\Delta q/T$ but I'm not sure why you can replace $\Delta q$ with $\Delta H$. From ...
2
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2answers
390 views

Molar heat capacity and heat capacity

Is molar heat capacity and heat capacity at constant volume both represented by $C_v$? at constant pressure both represented by $C_p$?
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1answer
20 views

What exactly causes equilibrium to shift when pressure is decreased? [duplicate]

Take the reaction: $$\ce{N2(g) + 3 H2(g) <=> 2 NH3(g)}$$ If pressure is decreased, equilibrium shifts to the left because it has more moles. I understand the basics of why this is, i.e. due to ...