Questions tagged [energy]
For questions relating to the energy required for or produced by reactions, including questions of endothermicity/exothermicity, bond enthalpy, etc.
472
questions
1
vote
1answer
76 views
Does energy come from fuel or oxygen? (surprise?)
Question: Is it oxygen or fuel that releases energy during burning?
The answer from this article:
Why Combustions Are Always Exothermic, Yielding About 418 kJ per Mole of O2 (Journal of Chemical ...
-1
votes
0answers
23 views
Are high energy-density rechargeable batteries possible with all reactants in the vapor phase, making them light-weight?
Is anyone working on rechargeable batteries whose components are purely in gaseous state except for their casing, i.e their energy-density being greater than or equal to the best batteries we have (Li-...
0
votes
1answer
23 views
Calculating bond dissociation enthalpy of F-F bond
$$\ce{N2 + 3 F2 -> 2 NF3} \quad ΔH = \pu{-263 kJ mol-1}$$
The bond dissociation enthalpies of the nitrogen triple bond and nitrogen–flourine bond are $\pu{946 kJ mol-1}$ and $\pu{272 kJ mol-1}....
-1
votes
0answers
29 views
How do i make molecular orbital diagram for (H2)+ when n=2?
Because hydrogen's atomic orbital is not affected by effective nuclear charge, placing the electron in the 2s orbital and 2p orbital results in the same energy.
When constructing molecular orbital ...
0
votes
0answers
33 views
What is meaning of LAV2P basis set?
I am working on energy optimization of molecular structure using DFT with Schrödinger software and I found that job is running on LAV2P basis set. I want to know what is the meaning of this basis set ...
-1
votes
2answers
55 views
What are the system and surroundings when dissolving sodium nitrate in water?
When sodium nitrate ($\ce{NaNO3}$) dissolves in water at room temperature, the
solution cools down. $\Delta H$ is positive because heat flows into the system during the process.
I thought though, ...
4
votes
1answer
183 views
Can I compare DFT calculations with different grids?
When doing DFT calculations, some integrations are commonly done numerically on grids. [In fact, more than a single grid may be used at the same time for different integrals, e.g. approximations such ...
1
vote
0answers
14 views
Reaction enthalpy using bond energy in resonating molecules
To find out and enthalpy of a reaction using bond energy we use the formula
$$\Delta H = \sum\Delta_\mathrm{bond}H_\mathrm{reactants} - \sum\Delta_\mathrm{bond}H_\mathrm{products}$$
since we use all ...
0
votes
0answers
29 views
Why is it easier to break a C-H bond of methane after another C-H bond has already been broken?
Bond energy explanations say the number given is often an average.
For instance, in methane, the $\ce{C-H}$ bond dissociation energy is the total energy required to remove all four hydrogens, ...
9
votes
3answers
927 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 ...
1
vote
0answers
53 views
How can the potential energy at the infinite energy level in an atom be zero?
I have recently learnt about atomic structure and the Bohr model of the atom and have observed a discrepancy between it and my previous knowledge based on physics.
For simplicity, assume the atom is ...
-1
votes
1answer
23 views
Prolonging the exothermic reaction between calcium oxide and water
Is it possible to generate 10-minutes of heat using very small amounts of CaO and water? This is an exothermic reaction.
I've done this experiment at home, but it is very short-lived. I'm trying to ...
3
votes
1answer
74 views
What actually happens when 'energy is released'?
Thermodynamics classes and equations always discuss a chemical reaction in the form of energy being released or absorbed. This is always hand-waved as just 'energy' from the surroundings.
What's ...
2
votes
1answer
323 views
Barron states that 4.18×10⁸ joules equal 1 kcal, is this correct?
Here is a paragraph in Barron's SAT chemistry prep book:
Work itself is measured in Joules, and so is energy. In some problems, however, energy may be expressed in kilocalories. The relationship ...
0
votes
1answer
32 views
Relevance of strain energy, total energy and stability of molecule?
Would anybody please highlight the difference between total strain energy of a molecule, total energy of a molecule and what we can infer about the stability of the molecule using the total strain ...
1
vote
1answer
36 views
Change in heat of photosynthesis
Consider a plant that uses the energy it receives from the sun to do work (to undergo photosynthesis) to produce glucose. The minimum amount of work this plant can do to produce 1 mole of glucose is ...
0
votes
2answers
58 views
Is the molar mass of a molecules lowered by the binding energy of the chemical bonds?
When calculating the molar mass, is there any measurable difference in total mass of the molecule due to the loss of binding energy?
6
votes
4answers
371 views
Colliding particles and activation energy
If two particles collide and they are under activation energy, why do they JUST “bounce apart”? Isn’t the activation energy steadily decreasing if those particles continuously collide?
I always ...
2
votes
1answer
42 views
Heat lost in evaporation at constant temperature
I ran an experiment evaporating salt water at different temperatures and concentrations. I’m trying to figure out how much energy is needed to maintain water at a specific temperature even when its ...
2
votes
2answers
56 views
Which substances have the highest/lowest enthalpy of formation per gram?
Which substances have the most extreme enthalpies of formation per gram at standard temperature and pressure?
0
votes
2answers
45 views
Ideal gas constant applied to water, lead, and other non-gases
I've asked a number of chemists why the ideal gas constant is in the equation for Gibbs free energy, and all say the same thing: "The name is a relic of the argon gas chamber used to determine energy ...
0
votes
1answer
66 views
Definition of Lattice Energy
From previous studies, I recalled in my lecture theatre today that lattice energy was the energy released when an ionic compounds is formed from individual atoms in the gaseous state. I thought this ...
-1
votes
2answers
97 views
Why are some reactions exothermic and some are endothermic? [closed]
Some reactions turn out to be exothermic or endothermic. But why does this occur? Why do some reactions need energy to bond but some release energy to bond?
8
votes
1answer
313 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{...
5
votes
1answer
127 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 ...
0
votes
1answer
372 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 ...
1
vote
1answer
22 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 ...
15
votes
5answers
892 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 ...
1
vote
1answer
142 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 ...
1
vote
1answer
40 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 ...
5
votes
4answers
158 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, ...
2
votes
1answer
82 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 ...
0
votes
1answer
72 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 ...
1
vote
2answers
92 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 ...
3
votes
2answers
101 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.
0
votes
4answers
136 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 ...
1
vote
1answer
458 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 ...
-1
votes
2answers
204 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, ...
4
votes
1answer
62 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 ...
-1
votes
1answer
66 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 ...
1
vote
1answer
181 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 ...
1
vote
2answers
63 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 ...
-2
votes
1answer
61 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 ...
0
votes
1answer
72 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 ...
-1
votes
1answer
57 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?
-2
votes
1answer
38 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 ...
2
votes
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 ...
2
votes
0answers
57 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 ...
-1
votes
2answers
358 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 ...
0
votes
1answer
117 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 ...
