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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Does pressure x volume = kinetic energy?

Sorry don't know if this is more for physics or here, essentially I had a question on the root mean square velocity of gas particles equation and didn't know what it was so tried to work something ...
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Why electrons do not distribute evenly among the atoms in a molecule?

I was wondering why the state where electrons are evenly (or the closest to being evenly) distributed among the atoms in a molecule is not the lowest energy state? For example, in a water molecule it ...
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Energy of valence electrons [closed]

I am currently studying Electrical Engineering and I have this question: An energy band is formed by the overlapping of atomic orbitals of atoms coming close to each other. I suspect that if the ...
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1answer
37 views

Why does higher temperature affect the rate of electrolysis?

I understand that more heat energy= higher rate of electrolysis, but can someone explain using higher-level terms why this occurs and if there are any theories or rules that explain this?
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How can I determine whether sp-mixing occurs for heteronuclear diatomics?

I'm trying to draw out the molecular orbital diagram of nitrogen monoxide (NO) but I do not know whether sp-mixing occurs. This is important in order to determine the arrangement of molecular orbitals....
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1answer
25 views

How to interpret this formula about hydrogen bond energy

I want to evaluate some chemistry related formulas, which I don't understand. In proteins, hydrogen bonding often occurs between the oxo group = O oxygen of one amino acid and the α-amino group (N − H)...
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Are all exergonic reactions spontaneous?

Exergonic reactions have a negative $\Delta G$: the system loses free energy. Spontaneous reactions are also defined in the same way, as far as I know. Does this mean the two are synonymous? There are ...
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1answer
149 views

Can vapour pressure be used to 'generate' work for free?

Given a bottle of water, a closed system, some of the water molecules in the liquid phase will have enough energy to escape that phase, forming water vapour, contributing to vapour pressure. Now ...
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37 views

Can the energy used required to break a molecular bond of plastic (e.g. - PVC) be used to dissociate plastics into its constituent elements?

Dear Molecular Chemists and Physicists, Pardon my ignorance, but why can not plastic polymers be broken down into their constituent elements? Common bond energies are shown in these two separate ...
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1answer
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Why use enthalpy?

I learned that Enthalpy is useful because it can be used to see the heat flow. But base on the formula, enthalpy change only equals to heat flow when in constant pressure. If the pressure is non-...
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1answer
69 views

Strength of the hydrophobic interaction

How strong is the "hydrophobic force"? Hydrophobic interactions are weak interactions but can have greater strength than hydrogen bonds. I find the strength of the hydrogen bond in ...
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51 views

Stability of an atom in absence of EM field

According to Bohr model of atom, electrons move up an energy level in presence of EM field and emit a photon moving down the level. In complete absence of any external EM field, shouldn't the electron ...
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1answer
29 views

Why constant volume combustion gives higher energy than constant pressure?

I have noticed when I have done some combustion equilibrium that enthalpy is higher when doing a constant volume combustion than pressure constant combustion. Why is it so ? What are the reasons ...
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1answer
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Finding Gibbs energy at different temperatures just given Gibbs energy at one temperature

How would it be found the Gibbs energy at a certain temperature, if they just give you another Gibbs energy at a temperature? For example: Given $\Delta G = -230 Kcal/mol$ at $773K$ for the reaction $...
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Why does Delta H change when the coefficients change in a reaction?

So I understand that if twice as much of the reactants are present, then twice as much energy is released. But isn’t the energy released per mole of reactant still the same? You are just scaling up ...
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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 ...
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Work done in expanding a gas reversibly and irreversibly

So, my chemistry teacher gave the class following $P_{external}$ versus $Volume$ diagrams for reversible and irreversible expansion of a gas which are as follows. (Reversible expansion) (...
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43 views

What is change in internal energy of a system in which combustion occurs at constant temperature?

We got a question in a test, in which we were asked which system has zero change in internal energy and it had an option which was combustion of methane at constant temperature. I imagined this to be ...
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A thermodynamics problem with an interesting equilibrium condition

Usually, when we analyze reactions, we assume that the reaction takes place at constant pressure or at constant volume. But there is no reason to assume this is generally the case, and so my friend ...
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1answer
52 views

A lot of confusion in 1st law of thermodynamics [closed]

My sir told me that Total energy of system = K.E + P.E in starting. Then Change in energy = F(External force on body ) * displacement of walls. Then from here , change in energy = W+q. (Don’t ...
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Help in understanding first way of changing the state of system

There is a statement in my book: THERMODYNAMICS One way: We do some mechanical work, say $\pu{1 kJ},$ by rotating a set of small paddles and thereby churning water. Let the new state be called $\...
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Finding excited stage of electron from its potential energy

The potential energy of an electron in the hydrogen atom is $\pu{-6.8 eV}.$ Indicate the excited stage in which electron is present. Total energy would be equal to $\pu{-3.4 eV}.$ I used the formula $...
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Where can I find the released combustion energy in NASA CEA rocket problem?

I am using NASA CEA program for a study project. I have read the CEA Nasa user's manual over and over, yet I haven't found an answer to my question which is : where can I found in the output of NASA ...
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1answer
45 views

Is there an actual specific heat for aluminum in its gaseous state? [closed]

I've scourged the internet and I can't seem to find it anywhere although I've found the specific heat values for aluminum in both solid and liquid states. I'm trying to construct a heating curve and I ...
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Why does the C−H bond dissociation energy vary in a homologous series of primary alcohols?

Specifically, for the primary carbon atom in the alcohol. Here is bond dissociation energy (BDE) data from chapter three of Luo's Comprehensive handbook of chemical bond energies [1] (boldface refers ...
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786 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" ...
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1answer
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Question to find increment in total energy of a sample of He gas? [closed]

If a closed rigid wall container filled with 20 gram of Helium gas moving at a constant speed of 10 m/sec is stopped abruptly to stand still, find the increment in temperature of this He sample. Way I ...
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1answer
110 views

How does heat transfer between molecules happen in deep?

Inside the container is cold water and outside the container is hot water. B is the microscopic view of container walls .W is water And A is hot water. What I have shown is the microscopic view of ...
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What is the fundamental difference between temperature and energy? [duplicate]

We know that temperature is proportional to the average kinetic energy of a system. We also know that temperature is not the same as energy because the temperature is intensive while the temperature ...
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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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1answer
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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
89 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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55 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
69 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
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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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291 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
51 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
208 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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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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51 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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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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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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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
98 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
31 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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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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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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