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

learn more… | top users | synonyms

5
votes
1answer
128 views

Periodically oscillating chemical reactions?

I've seen before chemistry demonstrations where solutions are mixed with one another and subsequently where the resulting product goes through periodic color changes: for example blue to orange and ...
1
vote
2answers
36 views

Energy of photons emitted by de-excitation of electrons

When an electron of an atom returns from an excited state to the ground state, it emits energy in the form of a photon. How does the change in energy level compare to the energy of the emitted photon? ...
6
votes
1answer
41 views

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

While studying the Crystal Field Theory I was told $D_q$ is a unit, related to the unit $\Delta_{\mathrm{O}}$ by the relation $\Delta_{\mathrm{O}} = 10 D_q$. But aren't $\Delta_{\mathrm{O}}$ and $D_q$ ...
6
votes
1answer
85 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, ...
4
votes
1answer
34 views

Why is it that less useful energy can be extracted in explosive reactions?

If you extract energy from a substrate (e.g. glucose) step-wise, a lot more free energy is released that can be used. However, if you were to do this in one single step, very little useful energy ...
4
votes
1answer
55 views

Burning a diamond produces how much energy?

How much energy is produced by burning a 1 ct. diamond? I'm trying to figure out how much energy to build the diamonds in a biological process. See here: ...
3
votes
1answer
84 views

Increase in Potential Energy When Bonds Are Broken

Why is it that the potential energy of a system increases when its bonds are broken? (I.e. when a solid turns into a liquid.) I thought the potential energy of the system was mostly contained in these ...
1
vote
1answer
48 views

Endothermic Conversion of Liquid to Gas

When a liquid (in my case I used butane) under high pressure is released into the air, it becomes gaseous, and the container seems to get colder. Why is it that turning a liquid to a gas requires ...
5
votes
1answer
66 views

Why is energy released as electrons move?

Why is it that energy is released from electrons when they move from one atom to a more electronegative one?
3
votes
2answers
301 views

Is the 'n' in Delta G = -nFE, ever negative?

Is it possible for 'n' to ever be negative? Trying to figure out where I went wrong on some thing and want to rule that out.
5
votes
0answers
47 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 ...
1
vote
1answer
43 views

Molar heat of fusion of ice?

The molar heat of fusion of ice is 6.01 kJ/mol. Can you explain what this means? What I think it means is that it requires 6.01 kJ to melt a mole of ice. I'm not positive though..
2
votes
0answers
31 views

In entropy change of surroundings, what is T?

This question is simpler than the previous one about intuition of entropy; I just need to know whether the $T$ term in $dS_{Surr} = \frac{-dH}{T}$ refers to the temperature of the surroundings or the ...
1
vote
1answer
29 views

Using enthalpies of formation and combustion to find formation enthalpy of Acetylene (Hess' Law)

I understand this is a simple question (I’m in high school), but for some reason the numbers just are not working for me. Given: $$\Delta H^\circ_\text{c} = -1301\ \mathrm{kJ}\ \text{for}\ ...
2
votes
0answers
24 views

Is Polymorphism accompanied with an energy change?

Differential Scanning Colorimetry (DSC) is a technique used to identify Polymorphism by revealing two melting points of a pure crystalline structure. DSC shows a peak associated with the formation ...
1
vote
0answers
29 views

Ionisation Energy (removal of electron) [closed]

My question is: Relate the ease of removal of an electron to the charge on the most stable ion formed by the element?
5
votes
1answer
63 views

Do core electrons in bulk material have discrete energy levels or continuous energy band?

The energy band of valence electrons gets smaller and smaller when the lattice (bulk) atoms are more and more separated from each other, until discrete energy levels are formed, due to the isolation ...
-3
votes
1answer
42 views

Calculating Energy Change of Acetic acid [closed]

A 10.0 g sample of pure acetic acid (CH3COOH) is completely burned. The heat released from the combustion is used to warm 2.00 L of water from 22.3 ℃ to 39.6 ℃. Assuming no heat was lost to the ...
1
vote
1answer
97 views

Relative energies between reactants and products

I've been asked to draw a relative energy sketch of the reactants and the two products. The reaction being examined was adding copper acetate monohydrate to glycine in two different fashions to create ...
2
votes
2answers
66 views

Are all naturally occuring reactions exothermic?

If a reaction is endothermic, then the reaction must take energy from the environment to occur (as far as I know), and if this is the case, then to me the reaction seems energetically unfavorable, as ...
0
votes
1answer
66 views

How much water evaporates In a vacuum before freezing?

I placed a container with 1000 grams (1 kg) of water at room temperature (20 degrees celsius) Inside a vacuum at 0.03 atm pressure. The water boiled for a few seconds then froze solid. I need to ...
0
votes
0answers
23 views

Why does the electron affinity increase in the 15th group

Why does the electron affinity increase by going down through the 15th group?
6
votes
2answers
127 views

Is most of the weight you lose actually released as carbon dioxide when you exhale?

I've heard that most of the weight you "lose" is actually carbon dioxide released when you exhale. In percent its much more than what is released in pure heat energy and feces. Does anyone have ...
0
votes
0answers
15 views

What is the heat of dissolution of sodium acetate trihydate?

Is the reaction endothermic since its crystallization is exothermic?
1
vote
1answer
19 views

Ideal gasses reaction under const temp and pressure

Conceptual problem: let $A + 2B \rightarrow C + 2D$ be a reaction under constant pressure (P) and temp (T), that goes all the way towards the products. A,B,C,D are ideal gases. let $\Delta H$ be the ...
4
votes
1answer
75 views

Safe yet strong exothermic reaction?

I'm studying chemical engineering at uni (Belgium), and this year (my 2nd) we have to develop and build a stirling engine. It has to be powered by a relatively safe exothermic reaction (not dangerous ...
2
votes
0answers
53 views

Why does the definition of ionisation energy only include gaseous atoms?

I know that in physics there is thermionic emission and the photoelectric effect. These are both method of removing electrons. I think these affects are only for metals due to their de-localized ...
3
votes
1answer
63 views

Can a reaction with positive Gibbs free energy change ever occur?

If you have an endothermic reaction with a negative entropy change, is it still possible to induce the reaction in some way despite the fact that the Gibbs free energy change is positive or all ...
1
vote
1answer
36 views

Entropy - Negligible?

In electrochemistry, the Nernst equation tells us the cell potential for non-standard conditions. I read that the factor $\frac{-RT}{nF}\ln{Q}$ accounts for difference in cell potential due to ...
1
vote
0answers
87 views

What is Barrier-less reaction in Quantum Chemistry?

After finding a reaction "Transitional State " by GAMESS and finding Hessian Eigenvalues, my project instructor said: " seems your imaginary frequency ( negative eigenvalue ) is not that big ( it is ...
1
vote
2answers
37 views

The relationship between energy and air pressure?

When boiling water at room temperature, what is the relationship energy has with the air pressure that is making the water boil cold instead of hot?
1
vote
2answers
68 views

Gibbs free energy or reaction enthalphy

If I conduct a reaction say, $$\ce{CaO(s) + H2O(l) \rightarrow Ca(OH)2 (aq)}$$ let us say , I want to measure the energy generated from the reaction.Will this energy I calculate equal the change in ...
6
votes
1answer
341 views

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

These 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#ixzz10Sh9iLQM ...
2
votes
1answer
130 views

What tools can be used to estimate binding energies?

I want to estimate the binding energies of various molecules. What are the analytical and numerical tools I can use for this purpose? In particular I'm interested in bonding energies of dyes to ...
3
votes
1answer
124 views

Gibbs Free Energy : What is it trying to say actually?

"Gibbs Energy is the useful work that can be extracted from the heat of a rxn or a thermodynamic process." I understand how it predicts the feasibility of a chemical rxn, considering the Entropy ...
3
votes
1answer
167 views

How To Get A Double Displacement Reaction Going

So this may be somewhat of a newbie question but here it goes. I was tasked with figuring out how to make some $\ce{NH4ClO4}$(ammonium perchlorate). I found that one way of making it was to react ...
1
vote
1answer
50 views

Comparing adamantane carbon types for accepting OH using MM ForceField

I want to compare two type of carbons accepting OH in adamantane which I've shown below. I know the blue position is preferred. But I wanna prove it with energy optimization and MM Forcefield. I ...
1
vote
1answer
61 views

How to calculate a reaction's DeltaH using a MM forcefield calculator software?

I want to calculate $\Delta H$ for hydrogenation of Benzene and producing Cyclohexane using MM+ Force Field Energy. I am using Hyperchem for energy calculation and optimization. I calculated the ...
2
votes
2answers
250 views

Which formula is correct for calculating the heat of dissolution?

I want to calculate the energy change when a solute is dissolved in water. I know that I can achieve this by using the equation $q=mc \Delta T$. My question is does the mass ($m$) change with the ...
1
vote
1answer
46 views

Why is activation enthalpy found and not just rate of reaction?

What is the benefit of finding activation enthalpy and not rate of reaction?
2
votes
0answers
52 views

First ionization energy of hydrogen molecule

If we have the dissociation's energies of hydrogen molecule $\ce{H_{2}}$($D_{0}$) and the corresponding molecule ion $\ce{H_{2}^{+}}$ ($D_{1}$) together with the first energy of ionization of hydrogen ...
2
votes
1answer
372 views

How to solve an Arrhenius equation problem?

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 ...
-1
votes
1answer
71 views

Why the second ionization energy of helium is greater than the first? [closed]

maybe because the first electron has a lower energy. Why does this happen?
2
votes
2answers
106 views

What happens when an explosion can't lead to volume increase of the thermodynamic system?

I have been searching for an answer to the question for a while but was not able to find 1. My question is: What if an explosion is not able to exit the container?-... so lets take a pipe bomb for ...
2
votes
1answer
105 views

Where does the energy of formation of covalent bonds come from?

Consider two $\ce{H}$ atoms. Since the proton in one attracts the electron in another, they attract each other, and form a covalent bond ($\ce{H}-\ce{H}$). Bond forming requires energy (436 kJ/mol for ...
1
vote
0answers
40 views

How is N to C ratio measured in forming austenitic stainless steel?

Well, gardeners and "green" people will think I'm talking about compost! Nitrogen is the future hope of stainless steel industry; since in the production of austenitic steel it can even completely ...
10
votes
1answer
476 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 ...
1
vote
1answer
113 views

Is the smallest or largest diameter important for the color of a molecule?

I learned that phenol absorbs longer wavelengths than benzene because the electron cloud is bigger. But what is about Penta-1,2,3,4-tetrien (1) and 2,2,-Dimethylpropane (2)? (1) has the largest ...
0
votes
1answer
38 views

Can we define a new unit instead of specific heat that is constant with temperature rise?

Specific heat plays an important role in calculating energy and thus, heat, enthalpy and etc. But as I sighted the definition for calorie, I was surprised. A calorie is the amount of heat needed ...
1
vote
1answer
55 views

Search materials by HOMO, LUMO and work function

I need to search organic semiconductors for organic photovoltaics (OPV) by their HOMO, LUMO, work function at 300K (as I understand, WF cannot be derived from HOMO and LUMO because semiconductor can ...