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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Why is effective nuclear charge used for explaining the periodicity of size of atoms and ions, even though radius depends upon many other factors?

The size of Na$^+$ is smaller than that of F$^-$ and Ne, as $Z_{eff}$ of Na$^+$ is higher than that of other ions. This is written at this site. But I don't understand how $Z_{eff}$ can be used as the ...
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31 views

Does pairing of electrons release or consume energy?

While studying Crystal Field Theory, it was said that low-spin complexes only form when the Crystal Field Splitting energy exceeds the pairing energy of electrons. What I infer from this is that it ...
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Which chemical reaction has the highest specific energy?

Which set of chemicals, reacting together, produces the highest amount of energy, per unit of mass of the substrates? Let's limit the substrates to reasonably stable chemicals (nothing like ...
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2answers
38k views

Strength of intramolecular vs intermolecular hydrogen bonds

Why are intramolecular hydrogen bonds weaker than intermolecular hydrogen bonds?
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1answer
123 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
91 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
146 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
5k views

Typical values of activation energies?

Where can I find typical values of the Arrhenius activation energy for arbitrary reactions? I only want to have orders of magnitude estimates, but so far I have not been able to find any good resource ...
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2answers
1k views

How much water evaporates in a vacuum before freezing?

I placed a container with 1000 grams (1 kg) of water at room temperature (20 degrees Celsius) inside a vacuum at 0.03 atm pressure. The water boiled for a few seconds then froze solid. I need to ...
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3answers
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Can carbon dioxide be reduced to carbon monoxide and oxygen to produce energy?

There are lots of questions about reducing or burning CO2 to carbon and oxygen to solve climate change, but of course that wouldn't work because it takes a lot of energy. But carbon monoxide is more ...
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1answer
54 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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4answers
5k views

How is chemical energy stored in carbon

I'm fairly new to chemistry, and I have a hard time understanding how chemical energy is stored in carbon (I'm aware that the question can be generalised to 'how is chemical energy stored', but I'm ...
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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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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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2answers
4k views

Carbonyl bond vs alkene bond

Why is that carbonyl bonds are stronger than those of alkenes? It's a basic question but I've never really thought much about it. I've read several times that carbonyl bonds are shorter and you need ...
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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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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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1answer
298 views

What's the minimum amount of energy needed to remove CO2 from the atmosphere?

I've been learning about CDR (Carbon Dioxide Removal) techniques to combat climate change. These all seem to involve extracting $\ce{CO2}$ from the atmosphere and converting to a mineral, which is ...
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1answer
2k views

How to calculate the Gibbs free energy from the equilibrium constant for the decomposition of sodium bicarbonate?

Solid $\ce{NaHCO3}$ is heated to $90~^\circ\mathrm{C}$. At equilibrium the total pressure of the gases produced is $0.545~\mathrm{atm}$. Calculate $\Delta G^\circ$ at $90~^\circ\mathrm{C}$ for the ...
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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
217 views

How to calculate a reaction's DeltaH using a MM forcefield calculator software?

I want to calculate $\Delta H$ for hydrogenation of benzene and producing cyclohexane using MM+ Force Field Energy. I am using Hyperchem for energy calculation and optimization. I calculated the ...
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2answers
569 views

Calculating Gibbs Free Energy

This is a question from Atkin's Physical Chemistry Book. Question Suppose that 3mmol $\mathrm{N_2\,(g)}$ occupies $\mathrm{36~cm^3}$ at $\mathrm{300~K}$ and expands to $\mathrm{60~cm^3}$. Calculate $...
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1answer
521 views

Change in internal energy of a gas upon expansion against a constant external pressure

I have a question about the following problem which I got wrong: During expansion of its volume from $\mathrm{1.00\,L}$ to $\mathrm{10.00\,L}$ against a constant external pressure of $\mathrm{2.00\,...
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1answer
11k views

Internal energy calculation

The temperature of 1 mole of a liquid is raised by heating it with 750 joules of energy. It expands and does 200 joules of work, calculate the change in internal energy of the liquid. I want to use ...
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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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1answer
42 views

Ideal gasses reaction under const temp and pressure

Conceptual problem: Let $A + 2B \rightarrow C + 2D$ be a reaction under constant pressure ($P$) and temperature ($T$), that goes all the way towards the products. $\ce{A,B,C,D}$ are ideal gases. Let $...
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1answer
22k views

How to calculate the temperature from heat of neutralisation?

The heat of neutralization of $\ce{HCl(aq)}$ by $\ce{NaOH}$ is $\pu{-55.9 kJ/mol}$ $\ce{H2O}$ produced. If $\pu{50ml}$ of $\pu{1.6M}$ $\ce{NaOH}$ at $\pu{25.15^\circ C}$ is added to $\pu{25ml}$ of $\...
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2answers
61 views

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
45 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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102 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
19k views

Formulas for the number of spectral lines

While reading through Narendra Avasthi's Problems in Physical Chemistry, I came across two formulas on p. 64 (Scanned page): When electrons de-excite from higher energy level ($n_2$) to lower ...
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2answers
15k views

Rate of exothermic/endothermic reactions

Is it necessary that all endothermic reactions be slow and all exothermic reactions fast? This is based on the fact that endothermic reactions require more activation energy than exothermic reactions ...
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1answer
119 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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546 views

Why energy is released when an electron is added to a neutral atom? [duplicate]

Question : Why energy is released when an electron is added to a neutral atom? I read somewhere “When electrons are added to an atom, the increased negative charge puts stress on the electrons ...
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137 views

Why does the C−H bond dissociation energy vary in a homologous series of primary alcohols?

Specifically, for the primary carbon atom in the alcohol. Here is bond dissociation energy (BDE) data from chapter three of Luo's Comprehensive handbook of chemical bond energies [1] (boldface refers ...
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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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79k views

EZ-Water - Fraud or breakthrough?

Recently the quack medicine folks online have been promoting the research of a certain Dr. Gerald Pollack who claims to have discovered a "forth phase of water", and who has recently published a book ...
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2answers
650 views

What is the first ionization energy of the hydride ion?

What is the first ionization energy for hydride? Since there are two electrons in the s orbital, I suppose it should be more stable than hydrogen, despite the extra electric charge, so the ionization ...
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6k views

Can natural gas appliances run on Hydrogen?

Can natural gas appliances run on Hydrogen? If so, does the appliance have to be modified and how significant of a modification would it need? Thanks
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2answers
240 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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4answers
13k views

Reason for inability to find the absolute value of internal energy

Today in my thermodynamics lecture, my teacher told me that it is not possible to find the absolute value of internal energy and so we have to calculate the change in internal energy. So, my question ...
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1answer
42 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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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?
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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: ...
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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 ...
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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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1answer
12k views

Bond dissociation energy order for C−C, N−N, O−O and F−F single bonds

Data from Chemistry LibreTexts — Strength of Covalent Bonds, Table 8.8.1: Average Bond Energies (kJ/mol) for Commonly Encountered Bonds at 273 K: $$ \begin{array}{cr} \hline \text{Bond} & D/\pu{...
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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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