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
534 views

What is J in the rigid rotor model?

In my class notes regarding the rigid rotor model, J is described as simply the angular momentum (replacing roe or p) and is also referred to as the angular momentum quantum number. Are these two ...
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0answers
21 views

Neither Raman nor IR Active vibrational modes of water [closed]

How can we find vibration modes of water that are not in IR and Raman spectroscopy? I thought these modes creat when a transition happens between 2 modes i.e from mode to another mode.
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3answers
443 views

Degree of dissociation of weak electrolyte at infinite dilution

Why the degree of dissociation of weak electrolyte is 1 at infinite dilution and how do we get the result? Like I know that at infinite dilution the concentration of solution is 0 but what does that ...
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2answers
67 views

Relation of temperature and intensive property [closed]

I came across a question that inquired about whether there exists any intensive property of a system, that is independent of temperature and then seeks proof for the presence/absence of such ...
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104 views

Anomaly in van der Waals constants of noble gases

In van der Waals equation for a real gas, the equation is $$\left(P + a\frac{n^2}{V^2}\right)(V - nb) = nRT$$ where $P$ is the pressure of the real gas, $n$ is the number of moles of the gas, $R$ is ...
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2answers
77 views

What does it mean to balance a redox reaction in acidic or basic mediums? [closed]

Until now it was clear to me what balancing a reaction was. Balancing redox reaction also make sense to me. What does it mean to balance a redox reaction in acidic or basic medium?
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32 views

Can we break double bonds by using laser and heat?

If it is possible then give an example for it. That chemical reaction is in this process. step 1: {Reactant + heat(sunlight)} gives weakened bonded product1 step 2: {product1 + laser} gives {one solid ...
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1answer
56 views

What all information can be gathered qualitatively from the radial distribution functions of a molecule?

Apart from knowing the radius of coordination shells and the probability of finding, is there any other thermodynamic information we can gather by looking at radial distribution functions of a ...
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0answers
51 views

How much CO2 can I fit in a 0.5 L plastic bottle?

Let's say I have a 50 lb CO2 tank which can probably contain about 1000 L of the gas at 122 atm. Suppose I want to use the tank to fill a 0.5 L plastic bottle which only has air in it. We know that ...
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1answer
53 views

How much oxygen is formed in this first order reaction? [closed]

We have a reaction $$\ce{2N2O5 -> 4NO2 + O2},$$ which has a rate constant $k=6,2\cdot10^{-4}/\mathrm{min}$ at temperature $T=318.15\ \mathrm{K}$. How much oxygen is formed in litres when $1.00\ \...
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1answer
31 views

Calculating ΔH with non-integer coefficients in the balanced equation

I am working a practice problem out Ebbing's General Chemistry and for part of the problem I needed to calculate $ΔH.$ The problem considers the burning of ethane in oxygen to yield carbon dioxide and ...
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1answer
93 views

How would one determine an element simply by looking at its binding energy?

I am self studying MIT OCW chemistry 5.111 2014, one of the lecture questions states the following: Consider a neutral atom with 8 distinct electron binding energies: −14 eV, −28 eV, −94 eV, −218 ...
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34 views

Interface level between 2 components in Liquid-Liquid Extraction, What does it mean?

In LLE physical processes, there is this level (interface) between the 2 components (for example) that is being separated as shown in the picture. I know that the height of this level from the ...
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1answer
75 views

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

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 ...
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2answers
55 views

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

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
29 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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2answers
2k 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 ...
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1answer
36 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'...
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1answer
107 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
66 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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2answers
42 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 ...
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1answer
112 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 $1/T.$ ...
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1answer
45 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
454 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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31 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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2answers
116 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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1answer
75 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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1answer
129 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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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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156 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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19 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 ...
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1answer
79 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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1answer
22 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?
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2answers
65 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 ...
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1answer
43 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 ...
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0answers
46 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 ...
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1answer
49 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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1answer
316 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 ...
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1answer
28 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 ...
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2answers
101 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 ...
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1answer
82 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
48 views

Feasibility of using ionic liquid fuels in an MHD type reactor

First off I would like to say that my knowledge on chemistry, even general chemistry, is basic if not poor. That said, I have some intuituions on this matter. I haven´t found any paper regarding ...
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1answer
45 views

Under what circumstances that Liquid-Liquid extraction would be good to use? [closed]

Under what circumstances that LLE would be useful ? Are the 2 top reasons - 1. Difference between the boiling points of the components are very low or similar. 2. For Temperature sensitive compounds ...
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1answer
57 views

Finding change in activation energy from change in rate constant in catalysis

I need to find by how much the activation energy decreases when the rate constant increases by a '$x$' factor when a catalyst is used in the reaction. I'm just super confused about how to solve this....
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0answers
180 views

Ground state term symbol, why is $L = |M_L|$, if L must be a maximum?

I'm trying to understand how to predict ground state term symbol of atoms. After finding the biggest S, why the biggest L will be $L = |M_L|$, where $M_L = \sum m_l$? I know this rule works to ...
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0answers
72 views

Energy of mercury(II) oxide decomposition

Study check 9.11 from [1, p. 298]: Mercury(II) oxide decomposes to mercury and oxygen. $$\ce{2 HgO -> 2Hg + O2}\quad ΔH = \pu{+182 kJ}$$ […] b. How many kilojoules are needed when ...
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1answer
48 views

Energy required for obtaining required mass of aluminium from alumina via electrolysis

How do I know how much energy I need to obtain 20 g alumunium from alumina with 5 V? I calculated the quantity of electricity is 2.22 F. Any help appreciated!
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1answer
47 views

Internal energy change for reactions at constant volume vs constant pressure

The reaction of cyanamide, $\ce{NH2CN(s)},$ with dioxygen was carried out in a bomb calorimeter, and $∆U$ was found to be $\pu{–742.7 kJ mol-1}$ at $\pu{298 K}.$ Calculate enthalpy change for the ...
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0answers
19 views

Could I make a lava lamp using diluted oil paint for the blobby part?

So, on a whim I decided to try making a lava lamp for my roommate. I know that lava lamps are made with dyed water/salt water and a trade secret mix of paraffin/wax/dye/heavy solvent that is just ...
2
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3answers
221 views

melting and boiling …really equilibrium? [closed]

Why are melting and boiling considered equilibrium processes even though the amount (concentration) of both phases keep changing i.e from solid to liquid and so on?

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