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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8
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1answer
176 views

When temperature is decreased, why do reactions occur at all?

I admit that my knowledge of collision theory may be lacking, but, as I understand it, when particles collide, a reaction will not occur without overcoming the activation energy. That being said, as ...
7
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2answers
548 views

Create my own solar cells?

How would I grow my own and build functional solar cells? I've read and researched that they're mostly a crystal structure of something like silicon. I would assume I'd be able to grow my own crystals ...
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2answers
953 views

Internal Energy vs Enthalpy

I struggle to see the difference between internal energy and enthalpy, or at least the need for differentiation between the two. I understand that enthalpy, supposedly unlike internal energy, accounts ...
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1answer
5k views

Why is it possible to form bromoalkanes but not iodoalkanes from free radical substitution?

For a free radical substitution (FRS) reaction between iodine $\ce{I2}$ with ethane and bromine $\ce{Br2}$ with ethane $\ce{CH3CH3}$: $E_\mathrm d(\ce{H-I})=299\ \mathrm{kJ\ mol^{-1}}$ $E_\mathrm d(\...
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34 views

Energy and time considerations in chemical reactions

I'm working on hydrothermal decomposition of organic matter at high temperature and pressure (400 bar). The reactions are too complex and numerous to model individually, but proceed in a similar ...
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0answers
35 views

What's causing my energy calculations to be wrong?

I'm calculating the energy density of certain flammable compounds in MJ/kg. To do this I compare the sum of the bond strengths of the reactants to the products and then extrapolate the energy density ...
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0answers
168 views

Rate constants using Arrhenius equation

If I'm trying to use the Arrhenius equation in this form: $$\ln\left(\frac{k_2}{k_1}\right) = -\frac{E_\mathrm a}R\cdot\left(\frac1{T_2}-\frac1{T_1}\right)$$ And I am given the activation energy ($...
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5answers
2k views

How much energy is stored when H+ is converted to H2?

I'm doing a write-up for this for my students: Source: Amirav Research Group (Facebook) The energy of formation of isopropyl alcohol is $-318.2~\mathrm{kJ/mol}$ (kilojoules per mole), that of ...
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2answers
921 views

How to explain Born repulsion between ions in gas phase?

In simple terms, the collision of two atoms $\ce{A}$ and $\ce{B}$ will result in ions $\ce{A^+}$ and $\ce{B^-}$ if $$I_a(\ce{A})+E_a(\ce{A})<I_a(\ce{B})+E_a(\ce{B})$$ where $I_a$ and $E_a$ are the ...
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2answers
5k views

What does the “total energy” of a molecule mean for the Chem3D MM2 minimized energy calculation?

I was fiddling around with Chem3D and the MM2 calculation for finding a molecules minimized energy. Benzene was assigned a total energy of -0.5741 kcal/mol while biphenyl was assigned a total energy ...
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0answers
86 views

What's the limit on energy density for chemical reactions?

Considering energy-releasing devices such as bombs or batteries which operate on chemical reactions and not nuclear (i.e. strong/weak) forces, what are the upper bounds on the amount of chemical ...
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1answer
1k views

Ratio of energy required for electrolysis vs creating water

I had an idea a while back for a machine that would be totally green. Powered by a Hydrogen Fuel Cell. A big question came up: Where do I get the Hydrogen? I assumed that I could just electrolysis of ...
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2answers
2k views

Difference between Gibbs Free Energy and Exergy

I'm wondering if there is any difference between Gibbs Free Energy and Exergy because their definition seems to me the same $\Delta H - T_\text{env}\cdot\Delta S$. Exergy represents the maximum ...
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5answers
3k views

What happens to a molecule while it is reacting?

I recently learned about the graph of activation energy that looks like this (source): I was wondering, what actually happens to the reactants as time passes on the graph? If we were to look at the ...
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3answers
289 views

When a thin lead sheet is hammered, what happens to internal energy

When a thin lead sheet is hammered, what happens to internal energy, does it increase, decrease or remains the same or first increases and then decreases?
4
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1answer
82 views

Is it possible to recycle an alkaline battery?

Is it possible to recycle an alkaline battery? The application I am thinking about is that in 3rd world countries often access to western markets is limited. You can't just pop into a store and buy ...
2
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1answer
198 views

Free energy change in collagen hydrolysis

In now-deleted comments on this answer, a user with a self-proclaimed chemical engineering background claimed that the reactions that take place when slow-cooking meat are endothermic and require far ...
0
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1answer
73 views

Excitation of an electron of H-atom from n=2 to any $n_2 $

I got taught that if an electron de-excites from any $n_2 $(where $n_2 >3$) to $n=2$, the energy change can be represented by $$\Delta E=13.6\left(\frac{1}{n_1^2}-\frac{1}{n_2^2}\right)\ \mathrm{...
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1answer
93 views

Given a theoretical combustion engine, how can I calculate the output of this engine depending on the fuel it uses?

I'm writing a Minecraft mod (for those who don't know, it's sort of like a smaller "program" that loads into the Minecraft game and expands it, by adding other things to it). My question is: consider ...
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1answer
716 views

Energy of hydrogen bonds vs. kinetic energy of water molecules

I watched an extremely engaging video "Why does ice float in water?" by George Zaidan and Charles Morton, https://www.youtube.com/watch?v=UukRgqzk-KE. In particular, video says "Below 4oC kinetic ...
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0answers
1k views

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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0answers
61 views

Is it possible to observe ATP energy transport in table experiment?

Is it possible to take AMP or ADP, then phosphorylate it convert to ATP to charge with energy, then transport to other place an then observe energy freeing? In table / home / school experiment?
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3answers
443 views

Does ∆Gº exist?

To the best of my understanding, the quantity of Gibbs free energy of an entity depends on its concentration in the system. Equilibrium is reached when ∆G = 0, or when the Gibbs free energies of all ...
4
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2answers
176 views

In equilibrium, if bonds are constantly being created and broken, where does the energy that does so come from?

I'm a student who recently learned about equilibrium and how it is not a state where nothing is made, but rather, a state where the product is decomposing at the same rate as the reactants are ...
4
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2answers
2k views

Where does the energy of formation of covalent bonds come from?

Consider two $\ce{H}$ atoms. Since the proton in one attracts the electron in another, they attract each other, and form a covalent bond ($\ce{H-H}$). Bond forming requires energy (436 kJ/mol for an $\...
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2answers
640 views

Endothermic and exothermic reactions

Today, in class, I learned about the two reactions. I know connecting bond releases energy, and breaking it requires and aborb/ consumes energy. But on my reference table I, 2C+H2 yielding C2H2 ...
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1answer
51 views

Reaction control on molecular level

Imagine I have a bottle with a random quantity of molecular hydrogen, and can apply exactly enough energy to break only one molecule of hydrogen. Is the reaction going to occur or the energy would be ...
2
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1answer
638 views

What is the difference between the chemical potential μ and the molar Gibbs free energy Gm?

I'm not too sure if I understand this correctly: Is the $G_\mathrm{m}$, the Gibbs free energy of the entire system, divided by the amount of substance making up the system, while $\mu$ is the Gibbs ...
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1answer
46 views

What are polydisulfide polymers?

What are polydisulfide polymers? How are these polymers applicable in energy sectors such as rechargeable batteries?
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1answer
614 views

Why can't hot water break disulfide bonds when the energy storage in hot water exceeds the bond energy?

I teach Biochemistry and know that heating water can break weak bonds like hydrogen bond or ionic interaction, but not disulfide bond (without reducing agent). The bond energy of hydrogen bond in ...
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0answers
173 views

How do ion–dipole bonds manage to break apart an ionic lattice?

I was reading this answer and its reasoning behind the dissolution of NaCl seems to lie in entropic favorability. However, as it states, many, if not most, dissolution reactions are favored by ...
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1answer
281 views

Lowering energy in molecular orbital mixing

When drawing molecular orbital diagrams for mixing two orbitals we always end up with one orbital which is lower in energy than the initial orbitals and another which is higher in energy. The ...
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2answers
2k views

How much energy is there in 1 mol of diamond and how can you get it?

Diamond is made of carbon which is during maybe 3 billion years under pressure is formed in the earth. Imagine you found a big source of diamonds such as coal...how much is the energy of the diamond ...
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3answers
12k views

kJ per mole or kJ per 2 moles?

From Chemguide: Is the measurement unit $\ce{kJ*mol^{-1}}$ correct here? Shouldn't it be measured simply in kJ, because the $-572$ figure is for the whole reaction, i.e. for 2 moles of the product?
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0answers
182 views

Is a substance's band gap related to it's flame test colour?

This is really not my field at all, but I am intruiged by the cause of different metals emitting different wavelengths of light. To my knowledge, the more energy needed to "excite" an electron, the ...
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0answers
319 views

How to calculate minimum temperature of a reaction?

For burning ethanol (its reaction with oxygen), we need a minimum activation energy (a minimum temperature) to start the reaction. Is it possible to calculate what are the minimum temperatures ...
4
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1answer
2k views

How are subshells and shells arranged in an atom?

If $\mathrm{2s}$ and $\mathrm{2p}$ are in the second energy level, and $\mathrm{3s}$, $\mathrm{3p}$, and $\mathrm{3d}$ are in the next (3rd) energy level, how are these subshells arranged in space in ...
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0answers
77 views

Confusion with degrees of freedom, some say CO2 has 9, others say 6 [duplicate]

My textbook doesn't consider vibration modes when determining the degree of freedom. Some other sources I have found don't either. But wikipedia, other sources, and even other users here apparently ...
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0answers
47 views

Can you derive a formula for any internal energy of a gas as long as you know the degree of freedom?

I have the following formula that I derived from studying my textbook that generalizes to all ideal gases: Monoatomic molecular gases ($\ce{He, Ne}$ etc.) Degree of freedom: 3 $\ce \frac{3}{2}nRT = ...
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1answer
101 views

“Exactly Equal” and “At Least” in electron excitation

When we examine IR spectra, we see troughs corresponding to absorption at exactly a specific frequency that corresponds to the energy needed to stretch certain bonds (although translational motions ...
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2answers
395 views

How does an energy input actually change a molecule?

I'm reading an online biochemistry textbook for fun, and a question that has bothered me on chemistry before popped up again. The question here is not specific for the chemical process described, but ...
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1answer
340 views

Finding the energy given out when 2 moles of reactants are mixed and ignited from a balanced equation

The question I am trying to answer is this: I only know about Hess' law, bond enthalpies and enthalpies of combustion and have tried to use all concepts in order to somehow get an answer but none of ...
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1answer
10k 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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2answers
1k views

Lattice Energy (enthalpy)

I know that when making a bond the reaction is exothermic (positive) and breaking a bond the reaction is endothermic (negative). Lattice enthalpy or lattice formation enthalpy is defined as the ...
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2answers
3k views

Physical Interpretation of Gibbs Free Energy

I know that $\Delta G = \Delta H - T\Delta S$ and that if $\Delta G$ less than $0$ a reaction will be spontaneous. What I am wondering is what is the actually physical interpretation of Gibbs free ...
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2answers
9k views

derivation of enthalpy internal energy relationship [closed]

A question asks us to derive a relationship between the enthalpy change and the change in internal energy for a reaction. Now, I know the relationship is: $\Delta H = \Delta U + V \Delta p + p \Delta ...
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0answers
65 views

If chemical reactions occur because everything tends to a lower energy state, why is there such a thing as equilibrium? [duplicate]

It just doesn't make any sense, if a reaction occurs because the reactants go into a lower energy state, then there should be no such thing as equilibrium. right? Because that would mean that the ...
0
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1answer
658 views

Energetics of Bond formation

Back to chemistry after 2 months and got stuck in the beginning! That's why I don't like it. Anyways, come to the question please. Following are the words from my textbook (Don't ask the name ;-) $...
4
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1answer
3k views

Why does attraction always cause release of energy making the system more stable?

Suppose $\ce{Na^+}$ and $\ce{Cl^-}$ form an ionic bond. In doing so they will come closer by attraction. Now as they come closer their speed will increase and hence the kinetic energy increases. So ...
4
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1answer
3k views

Difference between dissociation energy and dissociation temperature for water?

I was trying to find the temperature at which water dissociates into hydrogen and oxygen, and so I came across this Wikipedia page. It states that it takes 493.4 kJ/mol + 424.4 kJ/mol to dissociate ...