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
42 views

Spectral line width and lifetime

I am trying to find the lifetime of sodium atoms at the $3p$ state using the relationship between the spectral linewidth and the uncertainty principle: $$ \Delta E \times \Delta t = h / 4\pi $$ The ...
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1answer
31 views

Why does -TdS diminshes the useful work of an exothermic reaction? [closed]

$$\mathrm dG=\mathrm dH-T\,\mathrm dS$$ $$-100\ \mathrm J=-110\ \mathrm J+10\ \mathrm J$$ I assume that in an exothermic reaction which decreases the entropy of the system the heat transferred by ...
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1answer
43 views

What are the assumption of Gibbs free energy equation referring to the system and the surrounding?

The system for $\mathrm dG=\mathrm dH-T\,\mathrm dS$ is a constant temperature and pressure throughout the process, only volume work is possible and it is in thermal equilibrium with the ...
2
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2answers
65 views

What are Degenerate Rotational Energy Levels Physically?

I'm in introductory chem, so I don't have much of the physical background to really understand what's going on yet, but we're learning about rotational energy levels, and how some rotational energy ...
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0answers
34 views

What is the significance of the downward arrows in energy level diagrams in organic chemistry?

The following text is from Solomons, Fryhle and Snyder Organic Chemistry Third Edition, chapter 1 "The Basics: Bonding and Molecular Structure", page 13, topic 1.5 "Resonance Theory", sub topic 1.5B "...
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1answer
64 views

How energy is released when chemical bond is formed?

In books it is commonly written that whenever a chemical bond is formed the energy of the molecules/atoms gets lowered and hence energy is released. This is generally explained by diagrams like this ...
6
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1answer
124 views

What are computed energies in DFT and FF methods relative to?

I am not talking about zero-point energy. I wish to understand how the energy of a system is calculated relative to a zero baseline. This is best explained with an example. From DFT, the energy ...
3
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1answer
41 views

Surface energy for different crystallographic planes

For a given crystal structure, say body centred cubic, on what factors does surface energy of each plane depend? A basic approach considers the atomic density on each crystallographic plane, the ...
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0answers
21 views

How to calculate the energy to dissociate a bond into neutral atoms?

I am self studying chemistry through MiT ocw 5.111 . On practice exam 2 problem 2 there is a question which states the following ...
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0answers
38 views

Is kinetic energy proportional to temperature for non-gases?

If the molecules in a sample of ice at $\pu{-15 °C}$ and $\pu{1 bar}$ all have their kinetic energy doubled, then what is the final phase? The answer is gas, but I am not sure how to get this answer. ...
2
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1answer
43 views

Why does aluminum chloride have a higher lattice energy than aluminum fluoride?

From the table below (source: McMurry's Chemistry [1, p. 212]), it is evident that $\ce{AlCl_3}$ has a higher lattice energy than $\ce{AlF3},$ even though $\ce{F}$ is smaller than $\ce{Cl}$. Why is ...
4
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2answers
112 views

Regarding units of water potential and chemical potential

If water potential is nothing but the chemical potential of a given solution, then why do their units differ? If the unit for the latter is taken as 'Energy per molecule' (which makes sense to me ...
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1answer
38 views

Ground state elevation for phase transition

I have a question about the illustration from chem.libretexts.org: the ground states of the liquid and gas are offset from that of the previous state by the heats of fusion and vaporization, ...
3
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0answers
77 views

Is it possible to have a negative overall activation energy for a whole reaction mechanism?

I am trying to find out correlation for ignition delay for alkane fuels. The activation energy part of the correlation gives me a negative value. For the ignition delay formulation, is it possible to ...
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0answers
19 views

Energy Levels of Molecular Orbitals formed by combination of Atomic Orbitals

In general when we talk about chemical bonding, we say that it is "nature's way to stabilize the systems" and the energy of the molecule formed by atoms will be lower than that of the individual atoms;...
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1answer
36 views

Why should we be interested in catalyst for electrolysis?

I've been reading papers on Phosphided metals (CoP, NiP, FeP) as a catalyst for electrolysis. They increase the current density of the cell for a voltage. If it still requires 39.4 kilowatt-hours ...
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1answer
54 views

Combustion of carbon with hydrogen [closed]

Can coal (carbon) be "burned" in a hydrogen atmosphere? I know it would not match the definition of "combustion". But is the reaction $$\ce{C +2H2 ->CH4}$$ exothermic? (I'm fairly convinced this ...
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1answer
37 views

Nuclear physics [closed]

When considering Fusion, the matter that gets converted into energy what specific matter is converted exactly like a quark and is most of the energy created from the matter turning into energy?
4
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1answer
87 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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47 views

Literature value for the activation energy of the reaction between hydrochloric acid and sodium bicarbonate

Does anybody have the literature value for the activation energy of the reaction between hydrochloric acid and sodium bicarbonate? If yes, could you please cite the source for it and the value? I ...
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27 views

Electrons and Atomic Mass

Is the mass of electrons covered when talking about atomic mass. For example, the mass of Carbon is $12.011\space\text{amu}$. If this is including the mass of electrons (assuming the atom is neutral) ...
3
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2answers
63 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
31 views

Is it possible to convert carbon soot/ black carbon in mg to CO2-equivalent? If so, how?

Since global warming is expressed in terms of carbon emissions or CO2 equivalent, can the short lived carbon soot/ black carbon that is produced from incomplete combustion be expressed in terms of CO2 ...
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18 views

Relative Energies of Resonance Contributors & Stability of Borazine

We know that Borazine (Inorganic Benzene) is aromatic in nature. The following image shows the resonance contributors of borazine: What are the relative energies of these three resonance contributors?...
3
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1answer
117 views

Energy cost of C−N rotation in hydroxamate group

I am looking for a literature reference on the energetic cost of C−N rotation in hydroxamate group such in LC5 in water. I have been googling for a while.
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17 views

Interlayer binding energy: how to convert to meV/Ų?

I've noticed that in most papers the interlayer binding energy is given in units of meV/Ų. But how do I get these units? Do I divide the interlayer binding energy I get by the area of my unit cell?
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2answers
60 views

Catalyst that combines oxygen and hydrogen

Are there any known catalysts that can combine hydrogen and oxygen into water? Does this type of reaction have a name? Trying to search for information, it seems to be all about splitting hydrogen ...
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26 views

Carbon Capture Absorption with Henry's Law

Assume the Henry’s coefficient for water at $\pu{20 °C}$ is $\pu{1.6E8 Pa}.$ What is the mole fraction of $\ce{CO2}$ that will be dissolved in water assuming that it is at equilibrium with a flue gas ...
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2answers
91 views

How is energy not stored in bonds? [duplicate]

Consider the paraphrase from Ebbing: It takes energy to break bonds & energy is released when bonds are formed Let's look at the first statement It takes energy to break bonds. Is this true ...
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1answer
63 views

Why does the Heisenberg uncertainty principle work in an atom? [closed]

Where is my logic wrong? An electron can only assume quantized energies in an atom. If an electron is localized in space in a hydrogen atom, its radius is known. If its radius is known, its ...
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0answers
45 views

eV and redox potential

I am trying to estimate the redox potential of an excited state as described in this reference. The paper says: The reduction potentials associated with the excited states cannot be directly ...
2
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0answers
36 views

Bond Dissociation Energy in Water [duplicate]

Why do the bond dissociation energies of the O−H bonds in water differ? Is it related to an increase in lone pair-bond pair repulsions upon the breaking of the first O−H bond (decrease in stability, ...
2
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0answers
70 views

What is the largest known zero-point energy for a molecule?

I was surprised to find out that the zero-point energy (ZPE) for the ground state of $\ce{BH3}$ is a few thousand $\pu{cm-1}$, because for molecules I usually work with, it's much smaller. Does anyone ...
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0answers
54 views

Does the activation energy depend upon the stoichiometric coefficient?

For the decomposition of $\ce{N2O5(g)}$ it is given that $$ \begin{align} \ce{2 N2O5(g) &→ 4 NO2(g) + O2(g)} &\quad\text{activation energy} &= E_\mathrm{a}\\ \ce{N2O5(g) &→ 2 NO2(...
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23 views

what is the bonding energy of I2 and I3-?

I need some information of bonding energy. I found that the bonding energy of $\ce{I2}$ is $\pu{151 kJ/mol}$ (https://www.chegg.com/homework-help/dimethyl-ether-ch3och3-ethanol-ch3ch2oh-constitutional-...
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1answer
52 views

Why potential energy is neglected in this problem for calculating the energy difference between two stationary Bohr Orbits? [closed]

Question An electron in a hydrogen like atom makes a transition from a state in which its de-Broglie wavelength is $\lambda_1$ to a state in which its de-Broglie wavelength is $\lambda_2$, then ...
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0answers
93 views

What is total enthalpy?

I've seen that it's defined as $h_0 = h + \frac{v^2}{2}$, where $h_0$ is the total enthalpy per unit mass. I can see that the $\frac{v^2}{2}$ term probably has something to do with kinetic energy, but ...
3
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1answer
166 views

Rechargeable Battery Based on Neutralization Reaction of Acid and Base [closed]

The neutralization reaction, such as $\ce{HCl + NaOH → NaCl + H2O}$, generates heat, which is around $\pu{57.30 kJ/mol}$. Can we use this energy to design a battery? This idea occurs in my mind for a ...
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0answers
73 views

Why do the d orbitals contract when pairing of electrons start, because the size should increase due to increase in energy

The energy of an orbital is proportional to its mean radial distance, and since the 3d orbital is much larger it is much higher in energy than the 3s and 3p orbitals All references from JD Lee ...
3
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1answer
119 views

Relationship between Gibbs free energy and potential energy (related to reaction coordinate diagrams)

For a rate law, the rate constant $k$ is given by the equation $$\ln k = \ln A - \frac{E_\mathrm{a}}{RT}\tag{1}$$ If $k_\mathrm{fwd}$ is the forward rate constant and $k_\mathrm{rev}$ is the reverse ...
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2answers
75 views

Finding atomic number given energies of emitted photons

A hydrogen-like atom (atomic number $Z$) is in a higher excited state of quantum number $n$. This excited atom can make a transition to the first excited state by successively emitting two photons of ...
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0answers
68 views

What is the activation energy barrier of uncatalyzed nitrogen fixation?

I'm interested in the activation energy ($E_\mathrm a$) of uncatalyzed aqueous nitrogen fixation: $$\ce{3 H2 + N2 -> 2 NH3}$$ Biology performs this reaction with the nitrogenase enzyme at room ...
2
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2answers
121 views

Does energy come from fuel or oxygen? (surprise?)

Question: Is it oxygen or fuel that releases energy during burning? The answer from this article: Why Combustions Are Always Exothermic, Yielding About 418 kJ per Mole of O2 (Journal of Chemical ...
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1answer
144 views

Calculating bond dissociation enthalpy of F-F bond

$$\ce{N2 + 3 F2 -> 2 NF3} \quad ΔH = \pu{-263 kJ mol-1}$$ The bond dissociation enthalpies of the nitrogen triple bond and nitrogen–flourine bond are $\pu{946 kJ mol-1}$ and $\pu{272 kJ mol-1}....
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122 views

What is meaning of LAV2P basis set?

I am working on energy optimization of molecular structure using DFT with Schrödinger software and I found that job is running on LAV2P basis set. I want to know what is the meaning of this basis set ...
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2answers
86 views

What are the system and surroundings when dissolving sodium nitrate in water?

When sodium nitrate ($\ce{NaNO3}$) dissolves in water at room temperature, the solution cools down. $\Delta H$ is positive because heat flows into the system during the process. I thought though, ...
5
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1answer
226 views

Can I compare DFT calculations with different grids?

When doing DFT calculations, some integrations are commonly done numerically on grids. [In fact, more than a single grid may be used at the same time for different integrals, e.g. approximations such ...
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0answers
25 views

Reaction enthalpy using bond energy in resonating molecules

To find out and enthalpy of a reaction using bond energy we use the formula $$\Delta H = \sum\Delta_\mathrm{bond}H_\mathrm{reactants} - \sum\Delta_\mathrm{bond}H_\mathrm{products}$$ since we use all ...
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46 views

Why is it easier to break a C-H bond of methane after another C-H bond has already been broken?

Bond energy explanations say the number given is often an average. For instance, in methane, the $\ce{C-H}$ bond dissociation energy is the total energy required to remove all four hydrogens, ...
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3answers
2k views

Can Rydberg constant be in joules?

In my textbook (Chemistry Part - I for Class XI published by NCERT), there is an equation for the energy of an electron in an energy state: $$E_n = -R_\mathrm H\left(\frac{1}{n^2}\right)$$ and there ...