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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Comparison of energy release from different types of fuels

I've recently been reading about the different amount of energy release for different types of fuels/hydrocarbons. Anyways, I was wondering why butanol would release more energy (kj/mol) than methanol?...
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Delocalisation in Anti-Aromatic compounds

Recently, while solving questions on aromaticity, I came across a fact (as mentioned in the solution key of the question set) that there is NO DETECTABLE delocalisation in Anti-Aromatic compounds. ...
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I calculated internal energy at various temperatures and pressures. My results differ from someone else's. Is this OK?

I would like to make sure that my understanding of internal energy is correct. I'm not a thermodynamicist, so apologies in advance for what is probably a basic question. I previously calculated ...
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How do you know what elements will bond in a reaction? [closed]

I know all about the types of reactions, synthesis, decomp. etc., but when a bond is broken, how do you know that the free element will bond to another molecule? Is it because that element has a ...
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Solving the Schrödinger equation for a rotating triatomic linear molecule

This source is showing that solving the Schrödinger equation for a triatmoic linear molecule yields the same formula for the rotationaI quantum states $BJ(J+1)$ as for dipoles. For dipoles, the total ...
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The relation between q and T when the volume is constant [closed]

$$ \begin{align} q_V &= ΔU \tag{1}\\ q_p &= ΔH \tag{2}\\ C_V &= \frac{\mathrm dq_V}{\mathrm dT} = \left(\frac{\partial U}{\partial T}\right)_V \tag{3}\\ C_p &= \frac{\mathrm dq_p}{\...
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52 views

What does it mean for chemical reactions to release energy?

My Physics textbook gives the following definition of energy : The capacity of a body to do work is defined as the energy possessed by it This was the definition that was used to derive $U_G = mgh$ ...
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1answer
67 views

Calculation of free energy from potential and kinetic energy

I am having trouble understanding how (and even whether it's possible) to get free energy from kinetic and potential energy. I have run molecular dynamics simulations (NPT ensemble, CP2K software), ...
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Measurement of Energy Density

I'd like to ask how researchers measure/calculate the energy density for chemical fuels? Do they just measure the enthalpy change of combustion (△H combustion) in a calorimeter and then divide it by ...
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35 views

What does the alcohol functional group (specifically oxygen) have to do that causes an alcohol to have a lower energy content than an alkane? [closed]

My textbook said that the carbon is "partially oxidised" (don't really know what that means) and I just wanted to confirm.
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how to calculate the dihedral angle [closed]

I need to calculate the dihedral angle between C20 and C19, as well as between C19-C18. Can someone help me choosing the right combination? I have used the following one: C18C19C20C23 for the first ...
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31 views

Why are bonded ions more stable than separate ions? [closed]

I was reading on the Born-Haber cycle when I encountered a problem. The textbook seemed to suggest that since energy must be supplied to separate an ionic compound into it's composite ions, then the ...
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What is the link between the classical and quantum definition of the symmetry number?

From what I understand, the symmetry number for a molecule can be defined in 2 ways: 1. The quantum mechanical symmetry number corrects for overcounting the number of possible rotational states of a ...
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1answer
64 views

How do we figure out whether reactions are endothermic or exothermic? [closed]

Are the following reactions exothermic or endothermic: $$\ce{H2 + I2 -> 2HI}$$ $$\ce{N2 + O2 -> 2NO}$$ So I know the second reaction is endothermic as we need to break triple bonds between ...
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1answer
67 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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2answers
380 views

Pressure exerted by a particle of ideal gas

There is a step I fail to grasp in the proof that for a monatomic ideal gas, $U=\frac{3}{2}PV$, where $U$ denotes the internal energy of the gas. The proof involves considering a particle with mass $m$...
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29 views

What is the difference between enthalpy change and energy change? [closed]

This question seems really dumb but I rather be safe than sorry. I read about enthalpy change in my chemistry textbook which defines enthalpy change as the energy exchange between a chemical reaction ...
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13 views

Energy and impurities balance for adsorption with a fixed bed (with description)?

Do you have any suggestion where to look for a source of information about energy and impurities (component) balance for adsorption of mixture CO2/H2O in fixed bed? I have looked into many articles /...
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1answer
36 views

Is enthalpy affected by isotopes?

Enthalpy is a sum of $U$ and $PV$, and I thought that for different isotopes, internal energy values may differ. Is it true? There are three stable isotopes of $\textrm{Mg}$, mass number 24, 25, and ...
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49 views

Calculating Gibbs free energy for the reaction of burning methanol

Calculate $Δ_\mathrm{r}G^\circ$ for the following reaction: $$\ce{2 CH3OH(l) + 3 O2(g) -> 2 CO2(g) + 4 H2O(l)}$$ using $Δ_\mathrm{r}H^\circ$ and $Δ_\mathrm{r}S^\circ$ at $\pu{298.13 K}$ $(\pu{25 °C}...
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Covering conformers in a molecular modelling; consider them as a static entity or work with modelling shifts as well?

I am currently working with a molecular docking project, examining potential affinities of a solvent on a protein in an assay to evaluate potential error margin. The solvent is cyclohexanol (referred ...
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1answer
23 views

How value of energy of elecron becomes more negative and radius of orbit decreases with increase in the value of atomic number? [closed]

I know how energy of elecron and radius of orbit depends upon principal quantum number......But how it depends upon atomic number?
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1answer
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Does the absolute value of enthalpy have any physical significance?

I know it is pretty hard to measure the change in volume in open systems. Accordingly, calculating the change in internal energy using the first law of thermodynamics is pretty hard also. Is this the ...
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1answer
52 views

Is the magnitude of ionisation enthalpy and ionisation energy is same?

In my textbook it is written that ionisation energy and ionisation enthalpy are two different quantities. ionisation energy is the amount of energy provided to extract an electron from the outermost ...
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63 views

Why do stable compounds have a lower heat of combustion?

My brain somehow doesn't accept that more stable compounds require have less enthalpy. Isn't it like, if a compound is stable, it requires more energy to break the bonds because the compound doesn't ...
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22 views

Why is average bond enthalpy measured by homolytic fission?

Average bond enthalpy: the energy required for 1 mole of a specific gaseous bonds to undergo homolytic fission Why specifically homolytic fission? Is it to allow comparison, but if that were the case,...
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1answer
71 views

Difference between chemical energy and potential energy

I know that chemical energy is the potential energy stored in the arrangement of atoms within molecules. Forming new chemical bonds releases energy. what does potential energy mean? Is it the energy ...
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22 views

Meaning of chemical energy [duplicate]

I am trying to understand the meaning of chemical energy. I saw in my book that chemical energy is stored in the bonds of chemical compounds and when the bonds are untied the chemical energy increases....
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31 views

Change in temperature if salt is dissolved in water with different initial temperatures

I will mix a salt with room-temperature water and 8 degree Celsius water. Then I will compare the heat of solution with each other. Does the initial temperature of the water affect how much the heat ...
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20 views

Efficiency of H production from FeOOH catalyst?

Research has recently found that FeOOH is 25 times better at hydrogen production than titanium dioxide. Today, a new electrolysis plant delivers energy efficiency of around 80%. Is 25x the Honda-...
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1answer
61 views

Endothermic or Exothermic [closed]

Is an endothermic reaction always endothermic at all conditions of pressure, temperature etc.? Similarly for exothermic... I mean is sign of ∆H always the same as sign of ∆H°? This might seem to be a ...
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1answer
124 views

Values for heat of reaction example

I am currently studying the textbook Mass Spectrometry, third edition, by Jürgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following: Energetics of $\ce{H}^\...
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Why are there so many different formulations for energy? When do I use each one? [closed]

I understand that energy is a fairly arbitrary concept, and that it completely depends on your definition of energy. So far in my class, we have discussed: Entropy, $S$ (not really energy, but it ...
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1answer
187 views

How to figure out the most stable conformation of the diastereomer?

I guess my main question is looking only at the newman projection how does one determine the stereochemistry? In the molecule to the right, I get for the first carbon, (et, H, Me,) R ( I flipped it ...
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energy vs reaction coordinate diagram [closed]

To know the energy values-marked as ? and the coordinates-x,y for a given reaction ...
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2answers
103 views

The hydration energy of NaCl is −774.3 kJ. Then why are we not able to harness that energy and run machines just by mixing salt in water? [closed]

The hydration energy of NaCl is −774.3 kJ. Then why are we not able to harness that energy and run machines just by mixing salt in water? Where does all the energy go which is released when we mix ...
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1answer
58 views

Regarding the infinitesimal form of the First Law of Thermodynamics

First Law of Thermodynamics is expressed as[1] The internal energy of an isolated system is constant. If $w$ denotes the work done on a system, $q$ for the energy transferred as heat to the system,...
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74 views

Effect of intramolecular hydrogen bonding on the stability of a molecule

What will be the effects of intramolecular hydrogen bonding on the stability of a molecule? Will it increase or decrease the overall stability of a molecule? Or will it not have any impact on the ...
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1answer
184 views

How to determine the relative contribution of resonance structures when different rules give contradictory outcomes?

In order to determine the relative contributions of resonance structures, my textbook gives the following rules (in order): The more covalent bonds a structure has, the higher it scores. Structures ...
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1answer
32 views

Energy in chemical reactions [closed]

My question concerns how energy is used in chemical reactions. I am working with a reaction between magnesium and hydrochloric acid in a class (although this is not a homework question). What I've ...
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1answer
30 views

Can dissipative work be circumscribed as irreversible heat transfer

My question refers to an article I read yesterday in which the author states that for the calculation of the entropy change for a process (in that case friction, during an irreversible adiabatic gas ...
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1answer
96 views

How to find the lifetime of sodium atoms in the 3p using information on the spectral line width?

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
65 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 ...
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2answers
144 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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76 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&...
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2answers
127 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 ...
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1answer
148 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 ...
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1answer
66 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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1answer
135 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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39 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. ...

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