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

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32 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 ...
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1answer
16 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 ...
2
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1answer
26 views

What type of compound/element might be in these glowing tiles

I saw these tiles and these as well while surfing the net, they obiviously glow when their electrons are exited to a higher state and then de-exite over a long period to give off visible light. My ...
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2answers
23 views

Bond Potential Energy Lowering

"Bonds will form only if the potential energy will be lower when the atoms are bonded than when they are separate." Is this statement true? If so, how do endothermic reactions exist? Can't you add ...
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1answer
13 views

effect on kinetic energy of a body with change in temperature

Why doesn't the energy of a body doubles when temperature in centigrade is doubled? I know that it doubles in case of kelvin scale
5
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1answer
48 views

C-H vs C-C: which is stronger?

I've read that nonpolar bonds are stronger than polar ones. If it is true, why C-H bond entalpy (413) is bigger than C-C (348)? I'm very confused at the moment. Thanks a lot
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1answer
40 views

What conditions can cause a material to exist as a gas?

So my question is, how can something exist a gas. Is it when the pressure exerted by the gas is greater than the atmospheric pressure, then it is a gas? And also how do manometers work, how can you ...
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0answers
29 views

How to derive the energy of solvation equation?

The work done as a ion is solvated is given by: $-z^2e^2/8\pi\epsilon r$ but since the top line can be written $Q^2$, for simplicity I will say the equation is $-Q^2/8\pi\epsilon r$. Is this derived ...
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1answer
55 views

How to calculate the temperature from heat of neutralisation?

The heat of neutralization of $\ce{HCl~ (aq)}$ by $\ce{NaOH}$ is $\mathrm{-55.9~kJ/mol}$ $\ce{H2O}$ produced. If $\mathrm{50~ml}$ of $\mathrm{1.6~M}$ $\ce{NaOH}$ at 25.15 celsius is added to ...
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1answer
39 views

Transfer of energy

After completing a lab for my chemistry class I am finding it difficult to find the initial temperature of an iron nail after being heated. Procedure of the lab went as follows: heat an iron nail, ...
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1answer
38 views

“Orthogonality” of chemical elements

Chemical elements are said to be immutable at normal energies, but not at the energies that are orders of magnitude higher. Given that nucleus at normal energies gives us the Periodic Table and at ...
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1answer
45 views

Electron affinity

Concerning the liberation of energy when an atom that is close to the configuration of a noble gas: Where does the energy dissipated from an atom upon receiving an electron come from?
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1answer
33 views

Greatest Energy Output Reaction to Atmosphere Air

First of all i'm no chemist, this is not homework and if you need further clarification please ask. I'll be happy to provide! Imagine that you: have 1 kg of any given chemical X A car battery A ...
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0answers
71 views

Finding Root-Mean-Square of Ne using kinetic energy?

I am not being able to solve the following question: -Find the root-mean-square speed of $\ce{Ne}$ atoms at the temperature at which their kinetic energy is $\mathrm{6.24\ kJ/mol}$. I tried ...
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2answers
49 views

Energy Calculations using VIt

The answer for Energy in kJ = $2.5 \times 3600 \times 1 = 9000 kJ$ I do not understand what formula they are using... are they using $VIt$, where $V =12$, $t= 12.5 \times 60 \times 60$ seconds and ...
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1answer
53 views

Explicit differential equation based model of protein folding

I am an applied mathematician interested in the dynamics of potential systems - i.e., systems with multiple unique energy minima. One of the best examples of such systems are protein folding ...
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3answers
273 views

Is the transformation of pi bonds to sigma bonds always energetically favorable?

Is the move from pi bonds to sigma bonds always favorable? My professor claims so, except in the case of conjugated pi bonds. I can see how pi bonds going to sigma bonds might be favorable; I know ...
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1answer
63 views

ATP break down and energy release?

I have a very basic question. Energy is absorbed to break bonds. Bond-breaking is an endothermic process. Energy is released when new bonds form. Bond-making is an exothermic process. But ATP breaks ...
2
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0answers
40 views

Delta G values for Pyruvate--> Alanine vs. Oxaloacetate -> Aspartate ->Asparagine

What are the delta G values for the mammalian (human) biosynthesis of alanine from pyruvate, and for the conversion of oxaloacetate to asparagine? (assuming no particular cellular restriction or other ...
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0answers
53 views

Is S7H4 a chemical?

I want to find a chemical that will react with $\ce{SO2}$ to make water and pure sulfur to battle both greenhouse gasses and drought. I think $\ce{S7H4}$ would do it, but I don't know if it exists. ...
2
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0answers
106 views

Activation Energy of a rotting apple [closed]

A slightly bruised apple will rot extensively in about 3.5 days at room temperature (22.0 degrees Celsius). If it is kept in the refrigerator at 0.5 degrees Celsius, the same extent of rotting takes ...
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3answers
86 views

What really happens atomically in an explosion?

Let's say a room is filled with butane, I then throw a cigarette into the room. What happens to the atoms/molecules of the butane when they are in contact with the heat from the cigarette?
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2answers
184 views

How can I work out what reaction will happen?

I have recently started learning chemistry, and I've been reading a GCSE (UK high school level) textbook on the stuff :D Much of it has been fairly straightforward, though there has been a ...
2
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1answer
89 views

Why is ΔE described as Q-W and Q+W in different contexts?

Depending on the textbooks looked at, the energy change is described as either Q+W or the signage is changed to Q-W. Which is correct? Is it solely context dependent? Could anyone explain the ...
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2answers
106 views

What is the correct definition of the Gibbs free energy of activation?

Is the following correct? Gibbs free energy of activation is used in energy profiles where the stabilities of the species are expressed as changes in Gibbs energy, while the activation energy Ea ...
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1answer
141 views

Nitric Oxide Dimerization

This is the molecular orbital diagram for nitric oxide: Now, we know that nitric oxide can dimerize. However, why does nitric oxide dimerize as to form an $\ce{N-N}$ bond? Why not an $\ce{O-O}$ ...
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2answers
74 views

Nitrogen dioxide dimerization

$\ce{NO}$ can't dimerize and that is explained because the free electron is in an antibonding orbital. The same is true for $\ce{NO2}$, but it can dimerize, how?
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1answer
21 views

Calorimetry | Heat produced VS Change of enthalpy

There are two questions on the same test paper. Calculate the amount of heat energy, $q$, produced in the reaction Find the change of heat ($-q$). I'm not sure whether or not they mean the same ...
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3answers
55 views

Why cellphone batteries are still bad?

There are constantly new features in cellphones over the years, but it seems like batteries are not getting any better. Why is that?
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2answers
145 views

Counting Nodal Planes in cyclopropane

The energy of molecule orbitals increases with more nodal planes. W1 (in the attached picture) has no nodal plane. I'd like to know how to draw the nodal planes in cyclopropane molecule orbitals but ...
0
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1answer
62 views

Determining covalent bond strengths without hybridisation

Assuming pure $\ce{2s}$ and $\ce{2p}$ orbitals of carbon are used in forming $\ce{CH4}$ molecule, which of the following statements is false? (single choice question) Three $\ce{C-H}$ bonds ...
2
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1answer
106 views

Chemical bonding - lattice energy

Question: Why is ionic lattice energy inversely proportional to the radius of the atom? Most heterogeneous covalent molecules are polar to some extent. The degree of polarity, or the dipole moment, ...
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1answer
33 views

Is there a possible effect of low frequency mechanical vibration on the stability of organic molecules

Is there a possible theoretical effect of mechanical vibration on the stability of organic molecules. E.g. some medicines degrade if they are not stored in a fridge, is there a theoretical ...
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2answers
211 views

Is Bond Formation “Strictly” Exothermic?

Is bond formation "strictly" exothermic? The IUPAC definition of exothermic doesn't make any reference to bond formation. However, I have seen the aforementioned statement before - that bond formation ...
2
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2answers
126 views

Does any element have nutritional (caloric) value?

Is there any single element (e.g. possibly carbon) that can be eaten, which has nutritional value in that it provides calories? I found on Wikipedia that http://en.wikipedia.org/wiki/Dietary_element ...
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1answer
168 views

Why is the equilibrium constant wrong for this Gibbs free energy problem?

Solid $\ce{NaHCO3}$ is heated to 90°C. At equilibrium the total pressure of the gases produced is 0.545 atm. Calculate $\ce{ΔG°}$ at 90°C for the reaction $\ce{2 NaHCO3(s) ⇌ Na2CO3(s) + H2O(g) + ...
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1answer
83 views

How much heat is gained/released based off of equation?

Using this equation, $\ce{CaCl2(s) -> Ca^{2+}(aq) + 2Cl^{-}(aq)}$ and $\Delta H = - 325.0 \; kJ $ If you have 15.0 grams of the solid, how much heat is released or gained in kilojoules?
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1answer
1k views

What are some good research topics for a high school student?

I absolutely love chemistry and I really want to take part in science fairs. I am also taking an AP chemistry class. Cleaner fuel and energy sources and air pollution (especially due to smog and ...
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2answers
300 views

Does covalent character increase or decrease bond strength?

On one hand, covalent character increases the bond dissociation enthalpy (i.e., more energy is needed to be put in) and on the other it lowers the melting point of $\ce{Al2O3}$ to a value lower then ...
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1answer
54 views

What is the energy change of ethene reacting with hydrogen gas?

$\ce{CH2CH2(g) + H2(g) -> CH3CH3(g)}$ Using this table, source: http://www.kentchemistry.com/images/links/Kinetics/TB08_003.GIF ...
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1answer
100 views

How much activation energy is required to combust propane?

According to WolframAlpha, the change in enthalphy in the combustion of propane is -2220 kJ/mol. How do I calculate the activation energy required start the reaction in the first place? Do you use the ...
0
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1answer
50 views

What exactly happens to mass during deuterium fusion?

I know that the mass of Helium-4 is slightly less than the mass of 2x Deuterium it may be made of and that it is the reason fusion gives a lot of energy. But where exactly is this missing mass taken ...
2
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1answer
97 views

A reversible exothermic reaction between a molecule in an excited triplet state and a reducing agent

Say I promote a molecule to a triplet state via repeated electronic excitation events. Here, this is going to mean that an electron from the HOMO level, originally with a spin-UP and spin-DOWN ...
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1answer
75 views

Is there a relation between the ionization energy and the electron affinity?

I am aware of the definition and equation of IE and EA. I was wondering if there is a direct relation between this two quantities with the energy of the neutral specie.
3
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1answer
79 views

Endothermic and exothermic reactions

Today, in class, I learned about the two reactions. I know connecting bond releases energy, and breaking it requires and aborb/ consumes energy. But on my reference table I, 2C+H2 yielding C2H2 ...
3
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2answers
95 views

When a thin lead sheet is hammered, what happens to internal energy

When a thin lead sheet is hammered, what happens to internal energy, does it increase, decrease or remains the same or first increases and then decreases?
2
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1answer
51 views

Could this be a feasible fuel system?

First off, please forgive me, I am a chemistry novice! Overall Process Fuel for the system is distilled water Split water into Hydrogen and Oxygen (electrolysis or similar process) Exhaust Oxygen ...
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1answer
163 views

Activated Complex Products/Reactants

We know that an activation complex is the temporary unstable compound formed when activation energy is reached. But what dictates whether the products are indeed going to be products or if they become ...
3
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1answer
96 views

Why is ionization energy measured in gaseous phase?

When I looked up the definition of ionization energy, it says:- it is the energy required to remove one electron from the shell to infinity in an atom in gaseous state. Why is it measured in ...
3
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1answer
185 views

Thermodynamic stability of benzene ring

In learned that when benzene undergoes hydrogenation, $208KJ$ of energy is given off and thus $152KJ$ less energy than what would be given off if Kekule's structure was correct. My confusion is that ...