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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Is heat a form of energy or is it just a transport of energy, not energy itself?
In every textbook I read, it says that heat is a form/type of energy... but in lecture, my professor said, that there is no such energy as heat and that heat is just a method by which we can transport ...
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28 views
Modeling activation energy function
I'm quite new to the field, and actually am a mathematician. I was wondering if there is a way to model (find the equation of) the reaction progress (more specifically, the activation energy functions)...
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1answer
82 views
Why does activation energy depend on temperature? [duplicate]
To me it makes sense that the activation energy $E_\mathrm a$, as given by the Arrhenius equation, doesn't depend on the temperature as the needed energy (potential energy) to start a reaction has ...
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0answers
36 views
How can reversible reactions be exothermic or endothermic?
So this may be a dumb question, but because the forward reaction of a reversible reaction releases the sane amount of energy as the backwards reaction absorbs (because the bonds that are formed from ...
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1answer
29 views
Why does lattice enthalpy decrease with increasing ionic size?
Lattice enthalpy decreases as ions get larger, but I have found two explanations:
The charge density is greater in smaller ions, so greater attraction
The ions are themselves able to get closer ...
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1answer
48 views
Is hypervalency a real thing? [duplicate]
I saw a proper debate going on between answers to a question about whether the octet rule could be violated. Some people were pointing to hypervalency in period 3 elements, due to the available d-...
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2answers
95 views
Why energy is released when an electron is added to a neutral atom? [duplicate]
Question :
Why energy changes when an electron is added to a neutral atom?
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1answer
37 views
Can chemical energy from food be stored in a battery? [closed]
Suppose you built a machine that digested food in a similar way as humans do. Would it be possible, in principle, to extract the chemical energy from the digested food, turn it into electricity, and ...
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1answer
44 views
Does exchange energy affect completely filled orbitals?
In my textbook, it's written that exchange energy stabilises half filled and completely filled orbitals. But my teacher said electrons can't be exchanged in full filled orbitals because of pairing up ...
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3answers
2k views
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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49 views
Arrhenius Equation : Interpretation
Consider the relation:
$$E_{Activation}=E_{Threshold} - E_{Avg}$$
Here the $E_{Avg}$ refers to the Potential Energy of the reactants. Now in order of meet $E_{Threshold}$ , the molecules must have ...
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35 views
Arrhenius equation - Proper Interpretation of Activation Energy term
Consider the normal form of Arrhenius Equation:$$k=Ae^{-\frac {E_a}{RT}}$$
The term, $e^{-\frac {E_a}{RT}}$, is interpreted as the fraction of molecules having energy greater than Activation Energy.
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2answers
186 views
Why Does Activation Energy not change with Temperature change
As The Graph Shows; $E_a$ (Activation Energy) = Energy Of transition State(Threshold Energy) $-$ Energy of Reactants.
So let This be the graph at Temperature $T_1$, Now say We Increase The Temperature ...
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26 views
Why do internal energy/heat and enthalphy differ? What is the physical significance of the $PV$ term for enthalphy of an ideal gas? [duplicate]
Let it be noted that this is not a duplicate of this downvoted-to-hell question, simply because I hope to ask it better!
I've been reading a thermo textbook and I've got a simple question.
The ...
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1answer
66 views
How is resonance energy measured?
Is it the difference of energies of formation of the resonance hybrid and the average of the energy of formation of all the contributing structures? How would we even calculate the energy of a ...
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1answer
25 views
Comparison of energy release from different types of fuels [closed]
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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0answers
29 views
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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2answers
72 views
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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0answers
72 views
Solving the Schrödinger equation for a rotating triatomic linear molecule
This source is showing that solving the Schrƶdinger 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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2answers
59 views
The relation between q and T when the volume is constant [closed]
$$
\begin{align}
q_V &= ĪU \tag{1}\\
q_p &= ĪH \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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votes
2answers
68 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$ ...
2
votes
1answer
76 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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0answers
10 views
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 (ā³H combustion) in a calorimeter and then divide it by ...
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1answer
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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votes
1answer
60 views
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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1answer
35 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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0answers
24 views
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 ...
2
votes
1answer
76 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}$$
So I know the second reaction is endothermic as we need to break triple bonds between ...
3
votes
1answer
75 views
What's the minimum amount of energy needed to remove CO2 from the atmosphere?
I've been learning about CDR (Carbon Dioxide Removal) techniques to combat climate change. These all seem to involve extracting $\ce{CO2}$ from the atmosphere and converting to a mineral, which is ...
5
votes
2answers
396 views
Pressure exerted by a particle of ideal gas
There is a step I fail to grasp in the proof that for a monatomic ideal gas, $U=\frac{3}{2}PV$, where $U$ denotes the internal energy of the gas.
The proof involves considering a particle with mass $m$...
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votes
2answers
43 views
What is the difference between enthalpy change and energy change? [closed]
This question seems really dumb but I rather be safe than sorry. I read about enthalpy change in my chemistry textbook which defines enthalpy change as the energy exchange between a chemical reaction ...
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0answers
14 views
Energy and impurities balance for adsorption with a fixed bed (with description)?
Do you have any suggestion where to look for a source of information about energy and impurities (component) balance for adsorption of mixture CO2/H2O in fixed bed?
I have looked into many articles /...
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1answer
41 views
Is enthalpy affected by isotopes?
Enthalpy is a sum of $U$ and $PV$, and I thought that for different isotopes, internal energy values may differ. Is it true? There are three stable isotopes of $\textrm{Mg}$, mass number 24, 25, and ...
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0answers
57 views
Calculating Gibbs free energy for the reaction of burning methanol
Calculate $Ī_\mathrm{r}G^\circ$ for the following reaction:
$$\ce{2 CH3OH(l) + 3 O2(g) -> 2 CO2(g) + 4 H2O(l)}$$
using $Ī_\mathrm{r}H^\circ$ and $Ī_\mathrm{r}S^\circ$ at $\pu{298.13 K}$ $(\pu{25 Ā°C}...
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0answers
25 views
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
26 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?
2
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1answer
59 views
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
424 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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1answer
135 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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0answers
23 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,...
0
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1answer
136 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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0answers
23 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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0answers
34 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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0answers
21 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
62 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 āH always the same as sign of āHĀ°?
This might seem to be a ...
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1answer
125 views
Values for heat of reaction example
I am currently studying the textbook Mass Spectrometry, third edition, by JĆ¼rgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following:
Energetics of $\ce{H}^\...
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1answer
47 views
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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2answers
400 views
How to figure out the most stable conformation of the diastereomer?
Question 1: Which of the following Newman projections represent the most stable confirmation of the diastereomer of the molecule given below?
I guess my main question is looking only at the Newman ...
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2answers
120 views
The hydration energy of NaCl is ā774.3 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 ā774.3 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 ...
2
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1answer
78 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,...
