Study of macroscopic and microscopic phenomena in chemical systems in terms of physical laws and concepts [thermodynamics, statistical mechanics, kinetic theory, quantum mechanics...].

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Calculating Internal Energy of Formation

I'm working on some code to simulate combustion at constant volume instead of constant pressure and I need to calculate the internal energy of formation for the species involved because I can only ...
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Why is the molecular partition function only broken down into translational, rotational, vibrational, and electronic states, ignoring configurations?

Per Atkins and others, energy is the sum of contributions from the translational, rotational, vibrational, and electronic modes of motion. Since the formula for the partition function is $Q=\sum_i e^{\...
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129 views

Question regarding NaCl equilibrium separation

So I am tutoring someone later and one of the problems is from Eisberg/Resnick Ch 12. The potential energy $V$ of NaCl can be described emperically by $$V = \frac{-e^2}{4\pi\epsilon_0 R}+Ae^{-R/\...
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What is the position of hydrogen in the periodic table? [migrated]

Hydrogen is not in the first group as it was before and it is now placed above the periodic table? So why is it still categorized as a metal in some books?
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174 views

How to compute this change of Gibbs energy for a Van der Waals gas?

The change of Gibbs energy at constant temperature and species numbers, $\Delta G$, is given by an integral $\int_{p_1}^{p_2}V\,{\mathrm d}p$. For the ideal gas law $$p\,V=n\,RT,$$ this comes down to ...
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Theoretical Calculation of Specific Heat of a Gas

I've read that the theoretical specific heat of a monatomic gas (like dissociated hydrogen or oxygen) is $20.8\, \mathrm{\dfrac{J}{mol\cdot K}}$ at constant pressure and $12.5\, \mathrm{\dfrac{J}{mol\...
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30 views

How is the formula for percent ionic character derived? [closed]

How do the "-(0.25)" and the exponential come into play? Formula: Ionic Character = $100(1 - e^{-0.25(X_C - X_H)^2})$
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28 views

Where does the energy that release when bond is formed between two atoms come from? [duplicate]

When two atoms attracted to form bond, energy is released. But where does this energy comes from. Is this energy released when electrons goes to their ground state or somewhere else?
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53 views

How much approximately the pressure would drop?

A container made from from aluminium ($0.5~\mathrm{mm}$ thickness $10^3~\mathrm{cm^3}$) closed system , it has 50 psi (nitrogen) pressure inside at temperature $80^\circ~\mathrm C.$ Approximately : ...
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Is Gas flow rate or Volumertric flow rate right one to use for thick wall?

I will make container from steel or aluminium ( 0.5 mm thickness ) and fill it with air (2 bar) and I want to know how much pressure would the container loose overtime (20 years) ? I have asked this ...
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18 views

Is the bond order in a resonance situation an average or can half bonds exist?

When drawing the lewis dot structure for $NO_2^-$ There is one double bond and one single bond so the molecule exhibits resonance and has bond order of 1.5. Does this mean the molecule shares 0.5 ...
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266 views

Force field for calcium ions, potassium ions and water in molecular dynamics

I want to adapt my existing MD simulation so that it can handle these three species. For the interactions of the ions I thought that I would use the coulomb potential, but I don't know what sort of ...
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41 views

Avoiding a Divide by Zero with Absolute Entropy

I've been reading that unlike enthalpy, entropy has an absolute value that we obtain by setting it equal to zero at absolute zero temperature, but I'm having a hard time understanding how to avoid a ...
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762 views

Is the amount of the soil reduced when plants grow? [migrated]

According to the principle of mass conservation I think the amount of the soil should be reduced when plants grow. But this reduction is not observable so much. For example, some trees (big trees) ...
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2answers
54 views

Where can I find spectral data for materials?

The chemical library of ChemSpider has a dedicated section for spectra, but I haven't found any materials that have such data. Is there a (public) database of spectral data?
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17 views

Adiabation Flame Temperature Overestimation (Hydrogen Gas)

I'm working on some code that computes adiabatic flame temperature given a balanced equation and the relevant thermodynamic properties and I'm starting with the simplest combustion reaction I can ...
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155 views

reactions in molecular dynamics simulations

EDIT: Apparently this is called reactive molecular dynamics. It seems that the ReaxFF potential function is used for some reactions like this. I am interested in adding support for reactions to a ...
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69 views

How much pressure would I lose on one side?

The equation for the gas flow rate (in pressure*volume/time units) $$ Q = {kA\over d} (p_1-p_2) $$ where $A$ is the surface area, $d$ the wall thickness, $p_{1,2}$ the pressures on either side of the ...
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Is there a way to calculate the change in temperature of water in a vacuum?

My understanding is that water boils when the vapor pressure is reached and then, at some point, freezes. Is there a way to relate the vacuum pressure to the temperature of the water until it changes ...
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40 views

Why human body is not affected on magnetic field?

Electric-current easily cause shock to human body. But magnetic fluxs through human body do-not cause any perceptible change, as-well no invisible-impacts/ health impacts are well-known. We, when hold-...
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30 views

Question about the reaction quotients

I have a question connected with the reaction quotients. In another post (How to express the chemical potential at zero partial pressure?) it was revealed that the chemical potential of a substance is ...
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2answers
44 views

How does sawdust selectively absorb water?

This Wikipedia page states that sawdust, cellulose etc. can be used to absorb water from azeotropic ethanol to produce anhydrous ethanol. How does this work? Why would the sawdust not simply absorb ...
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28 views

How to express the chemical potential at zero partial pressure?

Does someone know how to express the chemical potential at zero pressure? In the expression of the $i$th component $${{\mu }_{i}}=\mu _{i}^{\otimes }+\int\limits_{p_{i}^{\otimes }}^{{{p}_{i}}}{{{V}_{m}...
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54 views

Why does the Gibbs free energy not decrease ad infinitum?

I would like to ask which guarantees if the Gibbs free energy has a minimum in closed system (e.g. in a chemical reaction system) at constant pressure and temperature? Why does it not decrease ad ...
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29 views

How can the energy released when bonds formed be harnessed to do work?

I'm trying to understand how living organisms get energy from food. I've heard that "energy is released when bonds form", but what exactly does "released" mean? If the energy dissipates in the form ...
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160 views

What's the relation between molecular orbitals and electron density?

The way molecular orbitals are drawn represent the "encapsulated" space in which the wave function has a significant amplitude. How do I obtain from this the electron density? Is there a fundamental ...
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Why does sound absorption in oceans depend on the pH?

I was reading "The Sixth Extinction: An Unnatural History", by Elizabeth Kolbert, and there she comments that high level of $CO_{2}$ in the atmosphere lowers the pH of oceans (which makes sense) and, ...
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563 views

How does the dissolution of salt affect the solution density?

Suppose you have a container of water as a solvent and you a certain amount of salt as a solute sitting at the bottom of the container that has yet to start dissolving. Supposing temperature and ...
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48 views

Why do molecules have $3N-5$ or $3N-6$ degrees of freedom?

In linear molecule, it has $3N-5$ degree of freedom in vibration mode and $3N-6$ in non-linear molecule. I can get idea about $5$ and $6$ which is related to translation and rotation but I cannot ...
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2k views

How is the number of electrons in an atom found?

I was wondering, what type of experiments were held to identify the number of electrons in an atom? (For example, how do we say that carbon has 6 electrons and magnesium 12.) I would like someone to ...
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122 views

On Thermodynamics of Spontaneity of the Reduction-Oxidation Chemical Reactions

According to the first and second law for a closed system containing different chemicals we have \begin{align} &\delta Q - \delta W = dU = T dS - p dV +\sum_i \mu_i d N_i\\ &\Rightarrow\;\...
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282 views

In a Monte Carlo NVT simulation How do I determine equilibration

I'm running an NVT (constant number of particles, volume and temperature) Monte Carlo simulation (Metropolis algorithm) of particles in two dimensions interacting via Lennard-Jonse potential ($U = 4(\...
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53 views

Total chemical potential of electrons in pn junction

I am reading this page about electron energy concept terminology. I am trying to apply that for the pn junction in equilibrium below. Could anyone help me to see if I get it correctly? C = ...
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68 views

The exact mechanism of energy release durning bond formation on the atomic level

Image a situation: We have two atomic hydrogen atoms. We magically collide them together dead center and perpendicular. Each atom has exact amount of kinetic energy. We collide them with precisely ...
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447 views

Ranking bond types from strongest to weakest

Note: I've already handed this in for homework and got the question wrong but don't understand why. Not looking for someone to do my homework for me, just trying to flesh out an area where I'm not yet ...
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3answers
396 views

Extra vibrational mode in linear molecule

When calculating the number of vibrational modes for a molecule, the formulas differ for linear $(n = 3N - 5)$ and non-linear $(n = 3N - 6)$ molecules, where $n$ is number of modes and $N$ is number ...
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48 views

global warming due to CO2 vs water

What is the physical reason for CO2 being a vital greenhouse gas when it is present at only approx 0.03% of atmospheric composition compared to water vapour, which is present at at least 100 times ...
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Why exactly does molten NaCl explode, when it is poured into water?

Why does molten NaCl explode, when it is poured into water? NaCl has high melting point, 1074 Kelvins (801'C). NaCl has molar mass 58.44 g/mol, it has specific heat capacity 36.79 J/(Kmol) = 629.53 J/...
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How to calculate the minimum kinetic energy required by a surface molecule to escape the liquid (during evaporation)?

Evaporation occurs when surface molecules have enough Kinetic Energy to escape the surface of the liquid. Given a certain volume of liquid at a certain temperature, is it possible to determine this ...
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why do microscopic cracks happen?

2 weeks ago i asked a question about " Gas permeation through solid metal? " i have got a very good answer here .but microscopic crack was mentioned in the answer. i searched in Internet but i didnt ...
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43 views

What's the minimum time scale for a candle to be lit in order for it to establish a steady state?

My Understanding When a candle is lit initially, it goes through a few stages (see, e.g. this explanation from the National Candle Association): Wick burns. Crusted wax on wick melts, evaporates ...
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2k views

How much heat from a fire actually warms your home?

A fire in a hearth disperses heat to, I guess, three places: the bricks of the chimney out the hearth (where the person tending the fire is standing) out the chimney, above the house How would you ...
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Determining bond length of HCN using rotational constant (Physical Chemistry 2)

Context: 2nd year undergraduate student taking Physical Chemistry II. Question: Determine the HC and CN bond lengths in HCN from the rotational constants: B($^{1}H$$^{12}C$$^{14}N$) = 44.316 GHz B($...
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2answers
48 views

Copper density modification

Can you increase the density of a material surface (metal) by surface treatment? For example commercial copper. If we take the ordinary OF copper (99.95%), I would expect not to have the tabulated 8....
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1answer
179 views

Gas permeation through solid metal?

if i make a box from aluminum ( 0,5 mm thickness ) and put air in it ( about 2 bar or 3 bar). would the box lose the air over time (10 years period) or not ? assuming the temperature will change ...
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25 views

Absorption spectra of molecules library

Do you know where I can find a library with absorption spectra? I would like it if then I could input a wavelength and get back a specific value. More specifically I would like to see the absorption ...
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51 views

Physical reason of adding salt when we're cooking rice (osmosis)

Why do we add salt when we're cooking rice? I know one reason is related to the boiling point of water but someone said it is also related to "Osmosis". What is the relation between adding salt and ...
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769 views

Solidification by the application of heat

When you add heat to a liquid (or a fluid), can it be solidified? If not, why in the world does an egg's stuffs become solid (or at least no more a liquid) when you 'boil' it in water?
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59 views

Velocity from the cumulative distribution function of the Boltzmann distribution

I want to get a Boltzmann distribution of the $v_x$, $v_y$ and $v_z$ velocity components (please, notice that the distribution is one-dimensional). To do so, I need the cumulative distribution ...