Questions tagged [energy]

For questions relating to the energy required for or produced by reactions, including questions of endothermicity/exothermicity, bond enthalpy, etc.

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1answer
88 views

How can a hydrogen atom ever emit an X-ray photon?

From Scientific American, February 2014: The Proton Radius Puzzle: ...we had to tune the laser so that it came in with exactly the right amount of energy. The atom would make the jump to the higher ...
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1answer
145 views

What is the average distance between electron 'shells' in an atom? Or between the innermost shell and the nucleus? [closed]

Somehow, I've never come across any mention of the actual, physical distances between, say the 1s and 2s shells in an atom, whether large or small.... I know that p, d and f (and g?) shells are oddly ...
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1answer
53 views

How is most probable radius in quantum mechanical model equal to Bohr's radius in hydrogen atom

Most probable radius in 1s orbital for hydrogen electron is $\pu{0.529E-10 m}$ which is Bohr radius. But energy of electron in hydrogen atom is proportional to mean radial distance in atom. In this ...
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0answers
26 views

What is the power density of graphite user the Wigner effect?

The energy that graphite released upon a cascade of defects by neutron radiation is 2.7 MJ/Kg, however there is no data on how quick this energy is released. I am interested in this as this not ...
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30 views

Are ekaconjugated polymers used as dielectrics? If not, why so?

So I came across an article called "Giant polarization in high polymers" and I was wondering if there was a reason why these types of polymers haven't found use in capacitors at this point. ...
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83 views

How change in potential energy corresponds to change in enthalpy?

So while reading about activation energy , I came across this graph : Here, change in potential energy of reactant and product is depicted as ${ΔH}$, but at constant pressure and temperature , ...
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0answers
31 views

Energy Balance for a reactor [closed]

There's wastewater flowing into the reactor at $\pu{20 ^\circ C}$ and the reactor is maintained at $\pu{36 ^\circ C}$. The effluent of the reactor flows into the stripper, which is at $\pu{65 ^\circ C}...
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1answer
79 views

Why doesn't an sp3s hybridisation exist?

Trying to prove that nitrogen doesn't split its lone pair to form 5 bonds, I thought of a situation that I couldn't rule out; the paired electron being excited to the 3s orbital, so that five bonds ...
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2answers
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Calculate Specific Heat given initial temp, final temp and equilibrium temp [closed]

I would appreciate if someone could enlighten me on this question. Question: A metallic object with a mass of 2 kg at 50ºC is placed in 10 L of water at 20ºC. When the thermal equilibrium the ...
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1answer
44 views

What exactly is the idea of gaining stability by the various chemical species?

When we consider the alkaline metals for example, we say that an atom of a metal like sodium gains stability by losing an electron, however this doesn't seem to be a very meaningful statement. Either ...
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100 views

Why is a C-N bond weaker than a C-C?

As far as I could remember, in the same period, a bond to a more electronegative atom implies in a more polar and stronger bond, due to the greater ionic character. However the bond dissociation ...
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1answer
114 views

Does mass affect rate of reaction?

Suppose I am reacting HCl with CuCO3. Experiment 1: I use 2g powdered CuCO3 Experiment 2: I use 4g powdered CuCO3 All other variables are kept constant. Will this have any affect on rate of reaction? ...
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1answer
310 views

Why is a sodium chloride molecule stable?

The ionization energy of sodium is $\pu{5.139eV}$. This is the energy absorbed when a neutral sodium atom is stripped of its outermost electron. The electron affinity of chlorine is $\pu{3.62eV}$. ...
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1answer
44 views

Change in Enthalpy when Pressure is constant

Okay so let me start from the beginning. I know that $ΔH= ΔU + p ΔV$ ( at constant pressure). Expanding $ΔU$, $$ΔH= q + pΔV + pΔV ~~~~~\text{(q at constant pressure)} \tag{1}$$ Next my chemistry ...
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2answers
87 views

How is kinetic energy accounted for when describing diatomic bonds with a Morse potential?

The Morse potential can be used to describe the potential energy of the a diatomic bond: This curve suggests that the lowest state $v = 0$ is the most stable, since it has the lowest potential energy....
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1answer
41 views

Do high-energy chemical bonds indicate strong chemical bonds?

In my head it seems reasonable that a high-energy bond would indicate that the bond is strong, however a question got me thinking. Take for example lead azide, a very explosive compound that is often ...
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52 views

CCSD and CISD size consistency problem

I have performed a Gaussian16 calculation to explore the size-consistency problem for the CISD and CCSD methods. The system I am studying is the water dimer and the results are not what I expected at ...
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1answer
55 views

What is the activation energy of creating molecular hydrogen from atomic hydrogen?

If molecular hydrogen is dissociated, or two hydrogen atoms in space collide, how much energy (in $\pu{eV}$, or perhaps $\pu{kJ/mol}$) does it take for an $\ce{H_2}$ molecule to form?
4
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1answer
222 views

Why is delta-H negative here?

Very basic question here, but I'm confused why Delta-H seems to be the reverse of what I would expect for bond enthalpy. For example, here's a problem in my textbook where the goal is to find delta-H: ...
2
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1answer
57 views

Second-step activation energy in SN1 reactions

In SN1 reactions, it's known that there are generally two steps, with the first being the R.D.S step involving carbocation formation and the next having a lower activation energy. Why does the second ...
4
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1answer
52 views

Why is the hydrolysis of ATP to AMP more energetic than the hydrolysis of ATP to ADP?

I am confused as to why the hydrolysis of ATP to AMP and pyrophosphate is more energetic than hydrolysis to ADP and inorganic phosphate, especially since pyrophosphates are more unstable than ...
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0answers
48 views

Cooling down from −78 °C to −88 °C without cryogenics

Say I have a gas cylinder with nitrous oxide and cool it down to −78 °C with dry ice. Is there an endothermic process/reaction that would extract the remaining heat from $\ce{N2O}$ and bring it down ...
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1answer
61 views

What did I do wrong in my temperature change calculations?

I am doing an online assignment where I am being asked to find temperature change but there is something wrong in my calculations as I am getting the answer wrong. Can someone help me figure out where ...
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0answers
46 views

Does the anti-rust properties of bluing carbon steel disappear at a certain temperature?

Yesterday I blued my new carbon steel wok over a very high (200K BTU) burner which is capable of getting the wok to 1000+ degrees with ease. I understand that bluing adds a rust-resistant layer which ...
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39 views

Maximum number of Spectral Lines “A better quantum model shows that there will be n^2 transitions”?

I was parsing the following post What is the maximum number of emission lines when the excited electron of a H atom in n = 6 drops to ground state? and came across with the reply from @porphyrin. cite ...
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How can I convert cathodic energy efficiency to overall energy efficiency?

Im working on calculation which involve the energy efficiency of producing formate by CO2 electroreduction. I wonder how to convert the reported cathodic energy efficiency (71%) of papers e.g (1) this ...
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27 views

How to calculate Energy Efficiency of electrochemical production

I'm trying to understand some basic electrochemistry as a non chemist and struggling to find the info online effectively. Its clear that energy efficiency = Energy(useful) / Energy (input). So, I know ...
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0answers
43 views

How much energy is required to operate a Sabatier Reactor?

I'm trying to model some industrial processes and having a hard time finding information about the Sabatier reaction. The sabatier reaction combines CO2 (and possibly CO) with H2 to produce H2O and ...
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2answers
111 views

Is it true that the better the trial function, the better approximation for the energy in variational principle?

While studying the variational principle in McQuarrie's Quantum Chemistry, I came across the following problem: to relate the difference between an approximation $\phi$ and the exact ground-state wave ...
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1answer
1k views

Why is it that protons and electrons undergo the same amount of deflection in an electric field if they have the same energy?

The question I have is with respect to this diagram. Which depicts a stream of protons and electrons entering a proton field with equal energy. Why is it that in the case where the energy of protons ...
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28 views

Can someone help me understand the motivation behind and visualize the dihedral potential and the Urey-Bradley potential?

I am studying statistical mechanics and force-fields, and I see a lot of this formula being thrown around with no explanation: $$U_{\mathrm{dihedral}} = \begin{cases} k(1+\cos (n\psi + \phi)),&...
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2answers
87 views

Why electrons do not distribute evenly among the atoms in a molecule? [closed]

I was wondering why the state where electrons are evenly (or the closest to being evenly) distributed among the atoms in a molecule is not the lowest energy state? For example, in a water molecule it ...
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1answer
87 views

Why does higher temperature affect the rate of electrolysis?

I understand that more heat energy= higher rate of electrolysis, but can someone explain using higher-level terms why this occurs and if there are any theories or rules that explain this?
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1answer
32 views

How to interpret this formula about hydrogen bond energy

I want to evaluate some chemistry related formulas, which I don't understand. In proteins, hydrogen bonding often occurs between the oxo group = O oxygen of one amino acid and the α-amino group (N − H)...
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0answers
39 views

Are all exergonic reactions spontaneous?

Exergonic reactions have a negative $\Delta G$: the system loses free energy. Spontaneous reactions are also defined in the same way, as far as I know. Does this mean the two are synonymous? There are ...
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1answer
162 views

Can vapour pressure be used to 'generate' work for free?

Given a bottle of water, a closed system, some of the water molecules in the liquid phase will have enough energy to escape that phase, forming water vapour, contributing to vapour pressure. Now ...
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45 views

Can the energy used required to break a molecular bond of plastic (e.g. - PVC) be used to dissociate plastics into its constituent elements?

Dear Molecular Chemists and Physicists, Pardon my ignorance, but why can not plastic polymers be broken down into their constituent elements? Common bond energies are shown in these two separate ...
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1answer
122 views

Strength of the hydrophobic interaction

How strong is the "hydrophobic force"? Hydrophobic interactions are weak interactions but can have greater strength than hydrogen bonds. I find the strength of the hydrogen bond in ...
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1answer
52 views

Stability of an atom in absence of EM field

According to Bohr model of atom, electrons move up an energy level in presence of EM field and emit a photon moving down the level. In complete absence of any external EM field, shouldn't the electron ...
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1answer
39 views

Why constant volume combustion gives higher energy than constant pressure?

I have noticed when I have done some combustion equilibrium that enthalpy is higher when doing a constant volume combustion than pressure constant combustion. Why is it so ? What are the reasons ...
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1answer
20 views

Finding Gibbs energy at different temperatures just given Gibbs energy at one temperature

How would it be found the Gibbs energy at a certain temperature, if they just give you another Gibbs energy at a temperature? For example: Given $\Delta G = -230 Kcal/mol$ at $773K$ for the reaction $...
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1answer
136 views

Why does Delta H change when the coefficients change in a reaction?

So I understand that if twice as much of the reactants are present, then twice as much energy is released. But isn’t the energy released per mole of reactant still the same? You are just scaling up ...
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836 views

Why do electrons jump back after absorbing energy and moving to a higher energy level?

Electrons in a shell absorb energy and move to higher energy levels, but they release their energy and jump back to the shell they originally were in. Why do they jump back? Why can they not keep ...
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3answers
124 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) (...
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1answer
75 views

What is change in internal energy of a system in which combustion occurs at constant temperature?

We got a question in a test, in which we were asked which system has zero change in internal energy and it had an option which was combustion of methane at constant temperature. I imagined this to be ...
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76 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 ...
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1answer
56 views

A lot of confusion in 1st law of thermodynamics [closed]

My sir told me that Total energy of system = K.E + P.E in starting. Then Change in energy = F(External force on body ) * displacement of walls. Then from here , change in energy = W+q. (Don’t ...
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43 views

Help in understanding first way of changing the state of system

There is a statement in my book: THERMODYNAMICS One way: We do some mechanical work, say $\pu{1 kJ},$ by rotating a set of small paddles and thereby churning water. Let the new state be called $\...
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27 views

Finding excited stage of electron from its potential energy

The potential energy of an electron in the hydrogen atom is $\pu{-6.8 eV}.$ Indicate the excited stage in which electron is present. Total energy would be equal to $\pu{-3.4 eV}.$ I used the formula $...
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Where can I find the released combustion energy in NASA CEA rocket problem?

I am using NASA CEA program for a study project. I have read the CEA Nasa user's manual over and over, yet I haven't found an answer to my question which is : where can I found in the output of NASA ...

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