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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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Which diatomic molecule would have the largest bond energy? [on hold]

Of the following diatomic molecules is I2 the molecule with the largest bond energy? F2 Cl2 Br2 I2
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1answer
305 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{...
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0answers
18 views

Transition from energy level [closed]

so when a hydrogen Atom is excited into the n=4 state how many transitions from this energy level are possible by emitting electromagnetic radiation? Is only one transition from this energy level ...
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0answers
12 views

Calculation of Photon frequency [closed]

If the binding energy in joules and the energy in joules for an element; chromium is given, how do you calculate the photon frequency needed to eject electrons?
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1answer
118 views

Energy of photons of given frequency and number

I’m having trouble with calculating the energy of $\pu{5.00e10}$ photons of frequency $\pu{1.00e9 s-1}$. I know that to calculate the energy $E = hf$ is to be used. However, I am unaware as to what ...
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1answer
50 views

What is the maximum number of emission lines when the excited electron of a H atom in n = 6 drops to ground state?

When an electron in a higher energy state jumps to a lower energy state in Bohr’s model of hydrogen atom, it emits a photon which has energy equal to the difference in the energy between the final and ...
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1answer
20 views

Overall enthalpy balance on a mixing process

Let's say I have a mixing process involving $\ce{A}$ and $\ce{B}$ at temperatures $T_\ce{A}$ and $T_\ce{B}$, respectively. The $\ce{AB}$ mix is at temperature $T_p$. Our $ΔH_\mathrm{mix}$ is defined ...
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5answers
623 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 ...
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1answer
75 views

Are the vibrational modes of CO2 active at room temperature?

I was doing an experiment whereby I had to measure the specific heat ratios of certain gases. Carbon dioxide came out to be around 1.3, and checking with the accepted values this is close. My question ...
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1answer
33 views

Why do reactions happen at all? [closed]

What makes some atoms/compounds reactive and some noble? What is the fundamental truth behind a reaction? It seems that two species can undergo number of combination to give a compound. Say Sodium and ...
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4answers
133 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, ...
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1answer
64 views

Formulas for the number of spectral lines

While reading through Narendra Avasthi's Problems in Physical Chemistry, I came across two formulas on p. 64 (Scanned page): When electrons de-excite from higher energy level ($n_2$) to lower ...
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1answer
37 views

What is the first ionization energy of the hydride ion?

What is the first ionization energy for hydride? Since there are two electrons in the s orbital, I suppose it should be more stable than hydrogen, despite the extra electric charge, so the ionization ...
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2answers
71 views

During formation and breaking of bonds, can the terms potential energy and bond energy be used interchangeably?

My chemistry professor uses these terms interchangeably and I was wondering if they refer to the same thing. From what I understand, bond energy is the energy required to break one mole of covalently ...
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2answers
92 views

Ea is the term for activation energy, what is the mean of a in this term?

Our doctor said it is not stand for activation. it stands for something else, any help will be appreciated.
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4answers
58 views

Adiabatic processes and the Ideal Gas Law [closed]

in my first year chemistry textbook it wrights that in adiabatic proccess when there is a system of canister filled with gas and a piston above(and wheights on it) if we let the piston move upward by ...
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1answer
95 views

Which has a higher lattice energy CaO or NaCl? [closed]

I know that as charge increase the lattice energy increases as well. However when the size increases, the lattice energy decreases. Can you please explain this to me? I think it is CaO but i'm not ...
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2answers
89 views

Why does bond breaking in ATP release energy? [duplicate]

We always come across that formation of bonds releases energy, and bond breaking requires energy, but in the case where ATP converts into ADP or AMP (bond breaking), energy is released. Why? Further, ...
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1answer
40 views

Correlation energy in quantum chemistry

In density functional theory (DFT) there is classic Coulomb energy and non-classic correlation energy. But what is difference between them? In books these energies are explained very similarly. Both ...
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1answer
60 views

What happens if the electron in the lowest energy level of an atom loses its energy?

What happens if the electron in the lowest energy level of an atom loses its energy? Excited states spontaneously give of energy and transition to a lower energy state. Why can't an electron in the ...
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1answer
78 views

Why are catabolic reactions exergonic and anabolic reactions endergonic?

Catabolism breaks apart large molecules and anabolism creates large molecules. Catabolism is supposed to be exergonic, while anabolism is supposed to be energonic. Id on't really understand this. By ...
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2answers
62 views

How do flame tests give off color if they only emit the colors when the electrons return to ground state?

Since we are constantly holding the element in the fire and the elements only give off the color when the electrons emit the energy that was supplied and return to ground state, why do we only see the ...
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1answer
50 views

How hydrogen molecule is formed? [closed]

How two hydrogen atoms come close to form a bond ? Textbooks refer to a potential energy diagram but what i cant understand is what is this potential energy if the atoms are neutral . How they come ...
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1answer
56 views

Confused about energy change diagrams

I have been reading about endothermic and exothermic reactions, as well as change in enthalpy. From what I have read, an exothermic reaction is where more energy is given out as bonds are made when ...
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1answer
44 views

Evidence for a chemical reaction

I know that the emission of light is evidence for a chemical reaction. However, are there any instances where emission of light can also be considered a physical reaction?
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1answer
34 views

Is it possible to turn food into fuel for a combustion engine? [closed]

According to McDonald's Nutrition Calculator page, the following order would contain 2480 kilocalories (or 10376 kilojoules): 1 x Double Bacon Smokehouse Burger 1 x Large Chocolate Shake 1 x Large ...
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1answer
45 views

Shape of the container and the number of possible energy states

A question came up when studying the formula for calculating the total number of possible energy states of a particle within a container. Why is the number of possible energy states independent of ...
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0answers
56 views

Calculating the number of energy states in a particular momentum direction

Given is a 2D scenario of a particle within a container: The circumference shows all the possible 2D spatial directions for a given momentum value of the particle. One of those momentum directions is ...
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2answers
182 views

Carbonyl bond vs alkene bond

Why is that carbonyl bonds are stronger than those of alkenes? It's a basic question but I've never really thought much about it. I've read several times that carbonyl bonds are shorter and you need ...
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1answer
68 views

Does the translational part of internal energy mean the kinetic energy of the gas?

Internal energy of an ideal gas consists of energy due to translational, rotational , vibrational etc. This line from WP says: In thermodynamics, the internal energy of a system is the energy ...
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1answer
23 views

Ionisation energy is lower for higher energy shell?

Why does an electron in a higher energy orbital require less energy to remove it? Wouldn't it be harder to remove an electron from a higher energy orbital when compared to a lower energy orbital?
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1answer
172 views

Why do the 4f and 5d orbitals have similar energies?

I've come to know this phenomena when learning about the exceptions to the aufbau principle. But there is no explanation of why 4f and 5d have similar energies (as I've read in some websites).
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1answer
27 views

Atoms in Solar Cells

An electric field in solar cells is created through photons knocking electrons off of atoms. What happens to the positively charged atoms once the electrons have been knocked off? Furthermore, are the ...
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2answers
489 views

Thermochemistry: What is the difference between the calculation of bond enthalpy and Hess's Law

so I know that hess's law is a indirect way to find the heat of reaction using the known heat of reaction of 2+ thermochemical equation, thus the formula is delta heat of reaction = enthalpy of ...
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1answer
1k views

Bond dissociation energy order for C-C,N-N,O-O & F-F single bond

I couldn't understand the trend of bond dissociation energy of various single bonds. Why C-C>N-N>F-F>O-O. I had mugged up the trend the now, and according to me BDE should continuously increasing ...
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0answers
76 views

Calculation Radial distribution function using Potential

I am trying to understand an article where it is describing the accuracy of a potential function obtained via a NN (neural network). To test the ability of the NN potential to describe also ...
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1answer
94 views

Thermal Conductivity of Calcium Carbonate?

Is Calcium Carbonate (Group 1 and 2) able to conduct heat more than other carbonate (Transition metal) allowing for them to be decomposed faster. The reason I am asking this question is because my ...
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2answers
91 views

Tunneling in chemical reactions

We know that quantum tunneling is the reason behind several natural phenomenon like alpha decay and thermonuclear fusion inside the stars. How can it influence chemical reactions by tunnelling a ...
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2answers
184 views

Does activation energy depend on steric factors?

I thought that activation energy depends on steric factors. By Arrhenius equation it must depend on steric factors since $A$ depends on steric factors. $$k=A\cdot\mathrm e^{-\frac{E_\mathrm a}{RT}}$$ (...
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1answer
106 views

How can chemical energy be stored in chemical things like candle wax, gasoline,…? [duplicate]

I have learned about a type of storing energy is chemical energy. But energy isn't sth we can see, can touch. It just simply gives the ability to work. So how can energy be contain in such chemical ...
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1answer
37 views

How can change in Gibbs free energy ever be positive?

I have a question regarding this formula for Gibbs free energy of a system: $\Delta$G = $\Delta$H - T$\Delta$S. According to the second law of thermodynamics: T$\Delta$S $\ge$ $\Delta$Q and to my ...
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2answers
308 views

Could a non-spontaneous reaction occur “on its own”?

Does spontaneity really only apply to the net free energy change of a reaction? I used to be taught that spontaneous reactions could occur on their own BUT without enzymes or a spark they might take ...
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1answer
68 views

Quantization and Bohr's model

According to quantization it's said that emitted or absorbed energy is quantized. Then, when it's said in bohr's model an electron changes its orbit (Let's say it goes to a higher energy shell from $...
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1answer
126 views

Energy at constant Entropy and Volume

The system of constant entropy and constant volume will attain the equilibrium in a state of minimum energy. Why? I know that: $\Delta G= \Delta H-T\Delta S$ And at constant volume and entropy: $\...
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1answer
61 views

Does the probability function for a molecule to have energy in a certain mode depend on the minimum required quantum energy level of that mode?

I understand that the probability density for a particular velocity v+dv in one dimension for a molecule in a system is: $$f(v) = \sqrt{\frac{m}{2\pi k_B T}} \cdot e^{\frac{-mv^2}{2k_B T}}$$ I'm ...
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2answers
218 views

Energy of activation vs Bond energy

In the second chapter, Methane Energy of activation and Transition state in the textbook Organic Chemistry by Morrison and Boyd, Energy of activation is given the following definition: The minimum ...
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1answer
793 views

Why the energies of orbitals in the same subshell decrease with increase of atomic number?

Why the energies of orbitals in the same subshell decrease with increase of atomic number? For eg., energy of 2s orbital of hydrogen atom is greater than energy of 2s orbital of lithium atom. What is ...
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1answer
65 views

Is there any difference between “autoignition temperature” and “ignition temperature”? [closed]

Is there any difference between the "autoignition temperature" and the "ignition temperature" of a substance?
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1answer
52 views

Reporting reaction energies calculated using electronic energies rather than enthalpies [closed]

I understand that electronic energy includes a combination of electron-electron repulsion energy, nuclear-nuclear repulsion energy, and electron-nuclear attraction energy at 0 K, and the energies ...
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1answer
76 views

Dissociation energy of benzene dimer

It is known that the benzene dimer has two stable structures, T-shaped ($\ce{C_{2v}}$) or parallel-displaced ($\ce{C_{2h}}$) structure. Now the question is: does the dissociation energy ($\ce{D_0}$) $...