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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87
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7answers
124k views

Why is the 2s orbital lower in energy than the 2p orbital when the electrons in 2s are usually farther from the nucleus?

My chemistry book explains that even though electrons in the $\mathrm{2p}$ orbital are closer to the nucleus on average, electrons from the $\mathrm{2s}$ orbital spend a very short time very close to ...
24
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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 ...
23
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3answers
7k views

How to relate a reaction barrier to the time the reaction needs to proceed?

As I am writing this I am at a conference and one of the participants just asked a question where he linked reaction barriers to durations for the reaction to complete. To paraphrase: From our ...
22
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1answer
2k views

If aliens lived in a hydrogen (or any flammable gas) based atmosphere, would they perceive oxygen to be flammable?

Energy, fuel, and oxygen are needed for a fire to burn. In a hydrogen chamber, if there was a pipe spewing small amounts of oxygen, could you light the oxygen on fire as it began to mix with the ...
19
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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 ...
17
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2answers
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 ...
17
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4answers
20k views

Is activation energy temperature-independent?

I know that activation energy for a reaction is the extra energy given to the reactants to reach the threshold energy so that they can collide and react. But then, why is it said that the activation ...
17
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2answers
39k views

In Crystal Field Theory what does Δo=10Dq mean?

While studying the Crystal Field Theory I was told $\mathrm{Dq}$ is a unit, related to the unit $\Delta_{\mathrm{O}}$ by the relation $\Delta_{\mathrm{O}} = 10\ \mathrm{Dq}$. But aren't $\Delta_{\...
16
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2answers
5k views

Why are there quantised energy levels in the vibrational energy of a molecule?

Why are the energy levels for vibrational energy in a molecule discrete as opposed to continuous? I don't understand how a vibration can't have continuous amounts of energy that depend on the ...
15
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3answers
912 views

What really happens atomically in an explosion?

Let's say a room is filled with butane, I then throw a cigarette into the room. What happens to the atoms/molecules of the butane when they are in contact with the heat from the cigarette?
15
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5answers
3k views

Define, (actually define) the “stability” and “energy” of a compound

When we say a conformer or compound is of "higher energy" than another, are we quantifying energy in terms of the bond strength? Or are we going off of how much energy it takes to break the bond? I ...
15
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1answer
3k views

Why six C atoms are usually seen in cyclic compounds?

When it gets to Carbon-based molecules, one very possible structure when there are more than six C atoms is the hexagon; though not mostly perfect, it emphasizes that six Carbon atoms tend to bond ...
15
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1answer
153 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 ...
14
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3answers
838 views

Why do electrons jump back after absorbing energy and moving to a higher energy level?

Electrons in a shell absorb energy and move to higher energy levels, but they release their energy and jump back to the shell they originally were in. Why do they jump back? Why can they not keep ...
13
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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 ...
13
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2answers
79k views

Does the potential energy increase when temperature is raised?

The potential energy of a material is its ability to do work. So I would suspect the potential energy to increase during phase changes that increase entropy (solid $\rightarrow$ liquid and liquid $\...
13
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2answers
12k views

Rotational degrees of freedom (3N-5 and 3N-6)

In spectroscopy we described the electric energy with the approximative separability of internal motions as: \begin{equation} E=E_e+E_v+E_r+E_{ns} \end{equation} (energies: electronic, vibratory, ...
12
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3answers
41k views

Is iron the most stable element in the periodic table?

According to the binding energy per nucleon vs mass number graph, it is observed that iron-56 has the maximum value of binding energy per nucleon ($\pu{8.75 MeV}$). It means that iron-56 is the most ...
12
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2answers
40k views

ATP break down and energy release?

I have a very basic question. Energy is absorbed to break bonds. Bond-breaking is an endothermic process. Energy is released when new bonds form. Bond-making is an exothermic process. But ATP breaks ...
12
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1answer
649 views

A theoretical molecule that could match uranium mole-for-mole

XKCD #1162 piqued my curiosity. Obviously, there's nothing we generally use as a chemical fuel that can match the energy density of uranium fission. But I wondered what it would take, hypothetically, ...
12
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2answers
5k views

Is the Gibbs standard free energy always constant?

I am a biochemistry student and we are learning about thermodynamics. Is the Gibbs standard free energy for a reaction always constant? The equation below suggests that it changes with temperature: $$...
11
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3answers
3k views

Is the transformation of pi bonds to sigma bonds always energetically favorable?

Is the move from pi bonds to sigma bonds always favorable? My professor claims so, except in the case of conjugated pi bonds. I can see how pi bonds going to sigma bonds might be favorable; I know ...
11
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1answer
11k 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 ...
11
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1answer
140 views

Should the mean energy be written in angular brackets or with an overline?

How would you write mean energy? I came up with two different ways: $\displaystyle\langle G_{\textrm{f}}^\circ(j) \rangle$ with the MathJax code ...
10
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3answers
6k views

Can Rydberg constant be in joules?

In my textbook (Chemistry Part - I for Class XI published by NCERT), there is an equation for the energy of an electron in an energy state: $$E_n = -R_\mathrm H\left(\frac{1}{n^2}\right)$$ and there ...
10
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3answers
53k views

Why is the Gibbs free energy for phase changes zero at constant temperature and pressure?

I get that $\Delta G$ measures the spontaneity/capacity of a system to do non-mechanical work, and that if: $\Delta G > 0$, the reaction is not spontaneous $\Delta G < 0$, the reaction is ...
10
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1answer
2k views

Does the “Bat Gen” claim to produce more energy than it uses?

The following links claim that inventor Arturo Solis Herrera has created an "everlasting battery". http://www.mexiconewsnetwork.com/news/bat-gen/ http://www.faqs.org/patents/app/20090134007#...
10
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1answer
370 views

Does liquids that emit light when vibrated exist?

I am looking for a liquid that illuminates when vibrations are added. It does not have to be strictly chemical, it might as well be something else as well. Maybe a crystal in powder form mixed with ...
9
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4answers
2k views

Where does the potential energy of capillary action come from?

Capillary action is when water pulls itself up a paper towel, glass tube or a tree. It is going up, which results in an increase in potential energy. According to the law of conversation of energy, ...
9
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1answer
357 views

Does the methyl rotation in propene have a symmetric or asymmetric potential energy surface?

Depending on how one imagines the methyl rotation of propene to occur, it seems like it could exhibit either a symmetric or an asymmetric potential energy surface. If the $\ce{H2C=CH\! -}$ portion ...
8
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5answers
7k views

Is Bond Formation “Strictly” Exothermic?

Is bond formation "strictly" exothermic? The IUPAC definition of exothermic doesn't make any reference to bond formation. However, I have seen the aforementioned statement before - that bond formation ...
8
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3answers
192k views

How can melting point equal freezing point?

I don't understand how the freezing point of a substance is the same temperature as the melting point of the same substance. For example, if liquid water freezes at 0 °C how can ice also melts at 0 °...
8
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2answers
4k views

Why is oxygen so special?

Why do reactions with oxygen produce flame (i.e. light), heat and hence a lot of energy? I mean, why only oxygen, why not any other element like nitrogen? What is special about the electronic ...
8
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2answers
25k views

Is it possible to light a match by scratching it on hard surfaces, like they do in movies?

In movies cool guys don't need a matchbox − they just light a match by scratching it on whatever hard surface − concrete walls, wooden bar tables, leather belts, etc. Is it just a movie trick, or is ...
8
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2answers
6k 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
17k views

How do I distinguish between internal energy and enthalpy?

I am finding it hard to distinguish between the two. Can someone explain the two terms and the difference between them? I tried learning from Wikipedia, but it said for both the above terms that it ...
8
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1answer
327 views

Why is the principal energy of an electron lower for excited electrons in a higher energy state?

Several places state the 'principal energy of an electron' can be calculated as such: $$E = \frac{2π^2mZ^2e^4}{n^2h^2}$$ Another equation I found was: $$E = -\frac{E_0}{n^2},$$ where $$E_0 = \pu{...
8
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1answer
1k views

Catalysist activation energy - the Brønsted-Evans-Polanyi relation

I have stumbled upon something called the Brønsted-Evans-Polanyi relation in a study about the design of catalysts (for reactions like those in hydrocracking fuel production.) The relation shows that ...
8
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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 ...
8
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1answer
2k views

What are B and n in this expression for charge repulsion?

In a study of the creation of ionic bonds of in this case $\ce{Na}^+$ and $\ce{Cl}^-$ into $\ce{NaCl}$, I have come across this equation for the overall energy of the system: $$E=-\frac{e^2}{4\pi\...
8
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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 ...
8
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1answer
191 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 ...
8
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1answer
150 views

Ballistic behavior of molecules on potential energy surfaces

I came across the following sentence in a publication$^1$: "At this point we have to remember that the computed MEP path [sic] represents the reaction in the absence of any kinetic energy, while in ...
8
votes
2answers
11k views

Which bond - C-C or C-H - is stronger?

I've read that nonpolar bonds are stronger than polar bonds. If it is true, why $\ce{C-H}$ bond entalpy ($\pu{413 kJ/mol}$) is more than $\ce{C-C}$ ($\pu{348 kJ/mol}$)? I'm very confused at the moment....
8
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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 ...
7
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2answers
761 views

Wouldn't radiolabelled phosphorus in DNA break it apart as it disintegrates?

The Hershey-Chase experiment was designed to prove that DNA is the genetic material in organisms. In this experiment, two batches of viruses were grown in two separate media A and B, with A having an ...
7
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2answers
34k views

Which has higher lattice energy: MgO or LiF?

Which has higher lattice energy: MgO or LiF ? A compound has higher lattice energy if it's ions have smaller size and greater charge Li cation is smaller than Mg cation => +1 for (LiF) Fluoride ...
7
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2answers
1k views

What are high-energy electrons?

I read that (in cellular respiration) the transported electrons in NADH have a higher energy than those in FADH2. I can't find a (simple or otherwise) explanation of what a "high-energy" ...
7
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2answers
229 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 ...
7
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2answers
3k views

Why exactly are standard potentials additive?

I don't really study chemistry so while my question may be very obvious, its not obvious to me. If we take an electrochemical reaction like $$\ce{2Fe^2+ + Au^3+ -> 2Fe^3+ + Au+}$$ we can find its ...

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