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For questions relating to the energy required for or produced by reactions, including questions of endothermicity/exothermicity, bond enthalpy, etc.

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Energy change during oxidation of Lithium

I came across this piece of text while reading about the reducing nature of Lithium. The process of oxidation may be thought to proceed as : $\ce{M(s)—>M(g)}$ ...
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0answers
17 views

The energy of ATP phosphate bonds [duplicate]

It is my understanding that there are two principal ways of how energy of bonds can convert into other kinds of energy: It's released as photons when electrons change their states - and photons can ...
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0answers
8 views

Titanium Dioxide Self Cleaning Reaction [on hold]

How does Titanium dioxide break down volatile organic compounds and nitrogen oxide? And what is the chemical reaction that occurs?
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0answers
33 views

hydrogen like atoms spectrum

this question appears in my textbook: one of the lines in the spectrum of hydrogen-like chlorine ion is attributed to an electron de-excitation from the 6th energy level to the 2nd energy level ...
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1answer
28 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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19 views

Specific heat capacity, internal energy and temperature

When metal and water are exposed to the sun for a certain amount of time , the metal will be burning hot from the sun, but the water will not feel as hot because they have different specific heat ...
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52 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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0answers
48 views

Observed activation energy of parallel and sequential reactions

I saw this sentence in a test: Observed activation energy, $E_\mathrm{obs}$, increases with increasing temperature for parallel reactions and decreases with increasing temperature for sequential ...
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2answers
59 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
40 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
16 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
77 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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42 views

Planck's Distribution Over a Range of Wavelengths

I am taking PChem this semester and I am stuck on this problem. Calculate the energy density in the range $\pu{650 nm}$ to $\pu{655 nm}$ inside a cavity at (a) $\pu{25 ^\circ C}$, (b) $\pu{3000 ^\...
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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
93 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
318 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
54 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
65 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
82 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
116 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
66 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
34 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
199 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
66 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
96 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
57 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
111 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
522 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
54 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
51 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
74 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 ($\ce{D_0}$) $...
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1answer
98 views

greater bond energy, more stable?

I am very confused about bond energy. In my book, it says "the most stable bond is the bond with the highest bond energy". However, later on it mentions that " A system with low energy is a stable ...
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1answer
67 views

When iodine replaces bromine in 2-bromobutane, does this lead to an overall lower energy level (electrons closer to nucleus) as well?

It seems to me that iodine is a nucleophile that replaces bromine because it has greater attraction to the carbon nucleus due to its electron properties. However, I thought that bonds are formed for ...
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1answer
40 views

What makes bond break apart from heat? [closed]

What makes bonds break apart from heat? I am wondering if anyone could explain the reasons why new bonds are formed in the absence of energy. I have found that they form in order to lower the overall ...
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1answer
250 views

Enthalpy of neutralisation for weak acids and weak bases at standard state

I recently read about why for weak acids and bases the enthalpy of neutralisation is less as compared to the strong ones. This was because the acids and bases being weak, they dissociate incompletely ...
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1answer
48 views

Enthalpy of formaton [closed]

today I was doing a set of HW problems regarding enthalpy and stumble upon one problem that I found confusing.It was the standard enthalpy of formation for CaCO3 is -1207.6 kJ mol when 30.7 g of ...
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2answers
285 views

Why does a neutral atom of beryllium not have any electrons in a p orbital?

Here's what I understand about quantum number and orbitals, please correct me if anything is wrong: Electrons enter into these different types of orbitals because they have a higher/lower amount of ...
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4answers
129 views

How do energy changes in reactions avoid violating the conservation of momentum?

As mentioned in this question, the idea of chemical potential energy explains how the thermal/kinetic energy of particles can change in a reaction; energy is taken in / released by the bonds broken / ...
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1answer
66 views

Can oxidation of hydrogen happen in room temperature? [duplicate]

Here is my explanation about the reaction between hydrogen or methane and oxygen. Hydrogen molecules and oxygen molecules can collide sucessfully and react if they have enough energy. In room ...
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1answer
53 views

What's the actual or official definition of activation energy? [duplicate]

In some sources I have seen that activation energy is the minimum energy required to cause a reaction. This implies that activation energy doesn't change with temperature (not considering very high ...
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1answer
71 views

How isotopes atomic mass was defined?

So we say that 1 Amu (u) = 1/12 of the mass of a Carbon 12 atom. Im not sure about this, but I believe that first we measured the mass of 1 carbon 12 atom (This includes the mass defects that occur ...
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41 views

Is it plausible to draw an enthalpy diagram for a nuclear reaction? [closed]

For a project I am required to draw a enthalpy diagram for the conversion of thorium-232 to uranium-233 and I am unsure on how to proceed. I understand a certain amount of energy is lost through beta ...
3
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2answers
52 views

Effect of doubling kinetic energy on phase transitions

The kinetic energy of the molecules in a sample of $\ce{H2O}$ in its stable state at $ \pu{–10 ˚C}$ and $\pu{1 atm}$ is doubled. What are the initial and final phases? [US National Chemistry ...
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2answers
404 views

Are the breaking of bonds simultaneously endothermic and exothermic? [closed]

I understand that energy is NEEDED to BREAK bonds. But don't chemical bonds already have some form of potential energy in them already? So wouldn't it make sense that even though energy is required to ...
3
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1answer
140 views

Am I Using the Correct Number of Significant Figures (Heat Problem)?

The question is: A patient arrives in the emergency room with a burn caused by steam. Calculate the heat, in kilocalories, that is released when $\pu{18.0 g}$ of steam at $\pu{100 °C}$ hits the ...
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0answers
60 views

Energy needed for electrolysis of aqueous NaBr [closed]

I'm trying to find the amount of energy it would take to electrolyse sodium bromide to get 1 mole of Br2. I'm not sure how to go about calculating this figure. If anyone could help me out, I'd be very ...
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2answers
80 views

How can atoms be influenced by light? [closed]

I was watching a SciShow video "Most dangerous Chemicals". It said that a compound called Azidozide azide explodes on being exposed to light. My question is: how does the the atom feel light. Heat can ...
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209 views

Is there a difference between chemical energy and chemical potential energy?

My physics teacher always insisted what was classically called ‘chemical energy’ in lower years, is actually ‘chemical potential energy’ as it has the potential to do work. Is there a difference? Is ...
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1answer
217 views

Energy balance for a system [closed]

A hydropower plant uses a river to generate electrical energy. It has a drop of $\pu{107 m}$ and the flow rate of water is $\pu{275 m3 s-1}$. The flow rate of the water is the same in and out of the ...
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1answer
344 views

Is the kinetic energy turning into activation energy when the reaction takes place? [closed]

So I want maybe a simple question that I had on a test today. For a reaction to take place it needs a minimum energy called activation energy. At school I heard that this energy is coming from the ...