Questions tagged [energy]

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

Filter by
Sorted by
Tagged with
4
votes
0answers
214 views

Difference between change in energy level and hyperfine energy level?

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. --> This ...
6
votes
2answers
7k views

Increase in Potential Energy When Bonds Are Broken

Why is it that the potential energy of a system increases when the bonds present in it are broken? (i.e., when a solid turns into a liquid.) I thought the potential energy of the system was mostly ...
6
votes
2answers
518 views

Thermodynamics: Relation between different types of energy: My Analogy

I have always been confused between the different kind of energies in thermodynamics so today I thought of finally getting it right. Here's my analogy(which is wrong and I need help in improving it, ...
4
votes
2answers
145 views

Can the number of intermediates for a reaction be more than the total number of transition states?

I'm getting results from a transition state guess software, in which the number of intermediates are two and there's only one transition state for a reaction, is that possible?
1
vote
1answer
551 views

Heat transfer with surroundings: why considered reversible?

I do not understand how the fact that the surroundings are large makes heat transfer with them reversible? I understand that the temperature of the surroundings is not going to change in the limit, ...
0
votes
1answer
86 views

C14 Nuclear Diamond to AA Battery Apples-to-Apples Engery output

I was reading an article about nuclear diamonds and they made an apples-to-oranges comparison of a 1 gram C14 nuclear diamond to a single AA battery. Here is the part I'm referencing: "An alkaline ...
2
votes
0answers
282 views

Why is polyacetylene an insulator?

Recently I have studied Huckel-theory and I appreciated how this approach is suitable to provide simple models to understand chemical behaviour. However, it is highly approximate and qualitative at ...
8
votes
1answer
2k views

Dangerous exothermic reactions at home

Exothermic reactions are essentially reactions that release energy as heat (in part, at least) to the surroundings, and may cause an explosion or combustion, depending on the amount of heat released ...
2
votes
0answers
59 views

How much energy can be produced by burning sewage gas?

I am an eighth grader. I need to make a science project on the production of electricity from sewage. I know that almost sixty percent of sewage gas is Methane and most of the other constituents are ...
1
vote
1answer
50 views

Determining the voltage of a cell

Setup: A magnesium electrode dipped in a magnesium sulfate solution and an iron electrode dipped into iron (III) sulfate solution Am I right in thinking that you need to first identify the redox ...
2
votes
1answer
144 views

Recommendations for electrostatic potential surfaces

Are there standards for density cutoffs, colours and colour mappings for electrostatic potential surfaces? I observe that people use many different values. For instance, this article (in Fig. 1a) ...
1
vote
1answer
57 views

When we say “the energy in a system” (in chemistry) do we mean the energy stored in the chemical bonds in the compounds present in that system? [duplicate]

Is it the energy stored in the chemical bonds of the compounds present in a system, that we refer to as the energy in/of a system ?
1
vote
2answers
845 views

Why does potential energy relate to exothermic reactions in this way?

I am not understanding how potential energy (which is the energy that results from position or configuration) relate to exothermic reactions. We say that exothermic reactions give off heat and so lose ...
1
vote
0answers
310 views

Finding threshold frequency of a metal [closed]

Find threshold frequency, in $\mathrm{Hz}$, of a metal if it emits an electron with kinetic energy of $2.74 \times 10^{-19}~\mathrm{J}$ when illuminated with light with frequency of $1.49 \times 10^{...
-1
votes
1answer
86 views

Do argon have a high energy? [closed]

Do argon have a large energy density? And what level is it on? Is it weak or have a density like gasoline. How much energy can argon store and what noble gas have the highest energy density?
1
vote
0answers
605 views

How can I calculate overlap integral (J) between fluorescence and UV-Vis spectra in FRET mechanism

How can I calculate overlap integral (J) between fluorescence and UV-Vis spectra in FRET mechanism? I want to use this formula: J=(∫ϵ(⋋) F_D (⋋) ⋋^4 d⋋)/(∫F_D (⋋)d⋋) How can I find ϵ(⋋) for every ...
5
votes
1answer
2k views

Molecular orbital diagram for nitrogen monoxide, the nitrosyl cation and the nitrosyl anion

As I understand it, all of them should have same order of energy of molecular orbitals as a model for $\ce{NO}$ should withstand ionization and adding an electron. JD Lee Pg 109 shows the same ...
3
votes
1answer
3k views

Thermodynamics of DNA double helix formation?

The entropy of a system decreases when 2 single stranded DNA molecules come together and form a double stranded molecule. For this to occur the total entropy of the universe must increase. Thus, heat ...
2
votes
1answer
478 views

thermochemistry - energy and enthalpy of different substances in water

I conducted an experiment in which I added Sodium Nitrate, Potassium Nitrate, Potassium Chloride, and Sodium Hydroxide - all separately into water - then measured the temperature change of each. The ...
3
votes
1answer
340 views

A reversible exothermic reaction between a molecule in an excited triplet state and a reducing agent

Say I promote a molecule to a triplet state via repeated electronic excitation events. Here, this is going to mean that an electron from the HOMO level, originally with a spin-UP and spin-DOWN ...
15
votes
1answer
152 views

Disregarding negative externalities and other barriers, what are some fuels that have a higher power density than gasoline?

Gasoline’s power throughput per kg is $12\,200\:\mathrm{Wh/kg}$ (Wikipedia.org). Are there any other fuels that have a higher power output that are not considered viable solutions as they are ...
1
vote
0answers
331 views

How to derive if the reaction is endothermic or exothermic based on rate constants at different temperatures? [closed]

Listed in the table are forward and reverse rate constants for the reaction $$\ce{2NO (g) <=> N_2 (g) + O_2 (g)}$$ \begin{array}{ccc} \text{Temperature}/\pu{K} & k_f/\pu{M^-1s^-1} & ...
-2
votes
3answers
112 views

In what circumstances and why do bonds break without an external energy source? [closed]

Edit: I've flagged my own question because it's too broad instead I'll split it up into more specific questions. So I'm trying to work out exactly how bonds are able to break when there is no ...
0
votes
2answers
79 views

Are heterolytic dissociations barrier-less or do they have an activation energy?

When a bond is broken into ionic fragments, and I'm specifically thinking about organometallic or coordination chemistry, the two products carry opposite charges and the potential energy curve should, ...
10
votes
1answer
6k views

Why do tetrahedral complexes have approximately 4/9 the field split of octahedral complexes?

I am trying to calculate the relationship between the octahedral field splitting parameter ($\Delta_\mathrm{o}$) and the square planar field splitting parameter ($\Delta_\mathrm{sp}$) and thought a ...
4
votes
2answers
145 views

Burning different isotope combinations of hydrogen and oxygen, how much does the energy vary?

In this comment I suggested that there would be a (very) small difference in energy released from burning a stoichiometric mixture of hydrogen and oxygen, depending on the isotopes, due to a slight ...
1
vote
0answers
257 views

Instantaneous enthalpy and entropy change of reaction as equilibrium is established

Can we calculate instantaneous difference between enthalpy and entropy of product and reactants of a reaction as the reaction proceeds towards equilibrium? Ex: $\ce{R<->P}$ reaction, at some ...
5
votes
2answers
3k views

Why are condensation reactions endergonic?

My lecture notes state that Condensation reactions, like all biosynthetic reactions, are endergonic. I am unsure as to why this would be the case. I thought bond formation was an exothermic ...
0
votes
2answers
207 views

How can you explain the energy change in this phenomenon?

Tagged is the diagram of the apparatus used in this thought experiment. Pure water is taken in one side of the beaker and a solution of common salt in water in the other. After a very long time, the ...
6
votes
0answers
489 views

How big is the gauche interaction of methyl with phenyl in a disubstituted cyclohexane?

I'd like to compare the equatorial 1-methyl-2-phenylcyclohexane conformation of with axial conformation of 1-chloro-3-methylcyclohexane conformation. In which molecule there is less steric repulsion? ...
3
votes
2answers
3k views

Can a reaction of the form A + B → AB ever be endothermic? [duplicate]

I understand that forming a bond between $\ce{A}$ and $\ce{B}$ is an exothermic process, with negative enthalpy, but won't there be energy required to get $\ce{A}$ and $\ce{B}$ close enough together ...
0
votes
0answers
503 views

Why only two modes of energy exchange?

In the thermodynamics chapter of the 11th standard, I read something that I have a hard time believing to be true: "There are two ways by which a system can interact or exchange energy with its ...
0
votes
6answers
17k views

Why is bond-breaking endothermic?

When electrons gain energy they become more excited and move to a higher energy level, which increases the tendency of an atom to form a bond with another atom. Thus, surely bond making requires the ...
2
votes
1answer
80 views

Heat exchange between tin and ethanol

This is a pretty straightforward heat/energy exchange problem, but I can't figure the answer out. A constant-pressure calorimeter contains $250.0\ \mathrm{mL}$ of ethanol (density = $7.89\ \mathrm{...
6
votes
1answer
126 views

What advantage is there in reporting the Lennard-Jones well depth in wavenumber units?

The Lennard-Jones well depth $\epsilon$ is typically given in energy units ($\mathrm{kJ}$ or $\mathrm{kcal}$; sometimes per mole). Jasper and Miller, however, reported $\epsilon$ values in reciprocal ...
8
votes
1answer
1k views

Difference between single point energy and dimerization energy

I am investigating potential energy surface characteristics of some electrostatic monomeric interactions e.g. $\ce{F-H}$...$\ce{F-H}$. I'm using DFT and SCS-MP2 to perform the necessary calculations ...
7
votes
2answers
5k views

Significance of single point energy when calculating interaction energies

I am currently investigating about the interaction behavior of a few atoms in certain conditions. Is it possible to use the concept of single point energy to represent the atomic interaction energies ...
8
votes
1answer
2k views

Understanding and usage of Arrhenius equation

A widely used rule-of-thumb for the temperature dependence of a reaction rate is that a ten degree rise in the temperature approximately doubles the rate. This is not generally true, especially when a ...
1
vote
1answer
460 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\,...
1
vote
0answers
90 views

Emission and Absorption Spectroscopy?

We're learning about emission and absorbtion spectroscopy, and how an emission spectrum is produced by passing a high voltage through a gas, and an absorbtion spectrum is produced by shining white ...
1
vote
0answers
199 views

Particle in a box models for polyenes and quantum dots [duplicate]

I'm kind of new to physical chemistry and trying to understand how, if at all, the correspondence principle (in the limit of large quantum numbers, quantum mechanics reproduces classical behavior of a ...
-1
votes
2answers
1k views

Is the change of the Gibbs free energy always zero (at constant pressure)?

At constant pressure, which is the usual condition for chemical reactions, heat absorbed/released by the system is the same thing as enthalpy change. According to the Gibbs equation, $$\mathrm dG = \...
-1
votes
1answer
1k views

What factors effect the energy change in a reaction?

The reaction of zinc metal and copper sulfate solution produces copper metal and zinc sulfate solution. What factors affect how much energy is given out for this reaction? So far I have:The mass of ...
1
vote
1answer
568 views

Energy levels database

Does anybody know where to find a database for atomic and molecular energy levels, with the corresponding energy values for each level? It would be needed just for small molecules. I tried the NIST ...
6
votes
1answer
25k views

How much energy is needed to break a water molecule?

How do you calculate how much energy is needed to break a water molecule into its constituent atoms? note This is not homework. I just want to know what is required to get hydrogen out of water.
1
vote
2answers
237 views

Why are higher-energy bonds preferred over lower-energy ones?

My chemistry book states that for example the bond S-O is preferred over the bond S-S because the first has a bond energy that is almost twice as the second one. Since the energy released by the ...
3
votes
1answer
161 views

What's with the weird definition for the Calorie? [duplicate]

I came across this definition for the calorie, which I found... strange: "The (15°) calorie is the heat required to raise the temperature of one gram of water from 14.5°C to 15.5°C." Subsequent ...
1
vote
1answer
619 views

Bond length and bond strength correlation

Is bond strength inversely proportional to bond length? As the bond length decreases, does the bond strength increase?
1
vote
0answers
34 views

Discrepancy in Standard Hydrogen Electrode energy

From Absolute Electrode Potential on Wikipedia: $$\ce{\frac12H2(gas) -> H+(aq) + e-(g)\quad(-(4.44\pm0.02)eV)}$$ The bond-dissociation energy of hydrogen is $\ce{4.52 eV}$: $$\ce{\frac12H2 -> ...
7
votes
2answers
200 views

Transition state - multidimensional surfaces

I've been reading an explanation about transition states in Smith's Organic Synthesis: A transition state is an energy maximum along the reaction coordinate. However, a chemical reaction where ...

1
5 6
7
8 9
11