instruction stringlengths 15 21.8k |
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Photosynthesis is obviously an endothermic reaction, I mean, what would be the point otherwise, right? This is probably just sheer and utter stupidity on my behalf, but why does Wikipedia say the heat of formation of glucose is negative? As you can probably see I'm on a quest of understanding enthalpy as a concept and ... |
Is photosynthesis endothermic and exothermic at the same time? ... somehow? |
In a <a href="http://en.wikipedia.org/wiki/Covalent_bond">covalent bond</a> between two <a href="http://en.wikipedia.org/wiki/Atoms">atoms</a>, an <a href="http://en.wikipedia.org/wiki/Electron">electron</a> from one of the either atom is shared by overlapping of their <a href="http://en.wikipedia.org/wiki/Atomic_orbit... |
Is storing carbon dioxide in limestone a good idea? Wouldn't that lead to a reaction like
$\mathrm{C}\mathrm{O}_2 + \mathrm{H}_2\mathrm{O}\to {\mathrm{C}\mathrm{O}_3}^{-2} + 2\mathrm{H}^+$
And then the (unbalanced) reaction
$\mathrm{Ca}\mathrm{C}\mathrm{O}_3 + \mathrm{H}^+\to \mathrm{C}\mathrm{O}_2 + \mathrm{C... |
If we take a **phenolate ion** ($\ce{C6H5O-}$) and an **acetate ion** ($\ce{CH3COO-}$) which one would be more stable?
Although the Phenolate ion has more(4) resonating structure compared to acetate ion(2), acetate is more stable because it has two equivalent resonating structure of same energy. My question is why d... |
Why does having equivalent resonating structure give more stability? |
Ions are electrostatically bound. One need only separate them with inegrated inverse squared distance work. If you mix multiple ionic compounds in solvent, a melt, gas phase, the original paired associations are spontaneously scrambled. Benzene plus xylene does not give you toluene. "Separating" benzene is not elec... |
This answer is intended to supplement [Manishearth's earlier answer](http://chemistry.stackexchange.com/a/445/83), rather than compete with it. My objective is to show how octet rules can be helpful even for molecules that contain more than the usual complement of eight electrons in their valence shell.
I call it do... |
#Preamble
One important thing to know is that what we call "resonance structure" is a byproduct of our chemical notation which can't describe effectively the structure of some compounds using only one chemical structure. Personally I find more appropriate the old term **mesomeric structure** (*meso-* Greek mésos in th... |
#Preamble
One important thing to know is that what we call "resonance structure" is a byproduct of our chemical notation which can't describe effectively the structure of some compounds using only one chemical structure. Personally I find more appropriate the old term **mesomeric structure** (*meso-* Greek mésos in th... |
So I have synthesised a compound which is basically a pyridine ring conected to a tetrazole. The procedure suggested to precipitate it at pH 1 but it didnt... It then suggested to extract it with ethyl acetate. The problem is that it is not going to the organic layer but into the aqueous layer! I have tried both at pH ... |
**THE STORY:**
A common example used to illustrate the limitations of restricted Hartree-Fock (RHF) theory is the H$_2$ dissociation energy ($D_e$) curves. RHF enforces electrons to be paired into spin orbitals, $\chi$, or two spatial orbitals $\phi$ with the same set of spatial coordinates $\mathbf{r}$ but a diffe... |
Is there an energy cost associated with flipping the spin of an electron? |
**THE STORY:**
A common example used to illustrate the limitations of restricted Hartree-Fock (RHF) theory is the H$_2$ dissociation energy ($D_e$) curves. RHF enforces electrons to be paired into spin orbitals, $\chi$, or two spatial orbitals $\phi$ with the same set of spatial coordinates $\mathbf{r}$ but a diffe... |
My textbook doesn't say anything about this but does say that on addition of organolithium compounds to carbon dioxide, they give ketones and not carboxylic acids like grignard reagents. This has been attributed to the greater nucleophilic character of Organolithium compounds compared to grignard reagents. I see that g... |
Why are organolithium and organomagnesium compounds nucleophilic in nature? |
This answer is intended to supplement [Manishearth's earlier answer](http://chemistry.stackexchange.com/a/445/83), rather than compete with it. My objective is to show how octet rules can be helpful even for molecules that contain more than the usual complement of eight electrons in their valence shell.
I call it do... |
The assumptions made in the [Flory-Huggins theory][1] are
- Quasi-solid lattice in the liquid
- Inter-changeability of segments (not necessarily the same as the polymer structure
units) of polymer and solvent molecules in the lattice
- Independence of lattice constants on composition (artificial)
- Polymer m... |
While studying about band theory of semiconductors, I observed that when the electrons were excited from the valence band to the conduction band, they left behind holes in the valence band. From my existing knowledge, I believe that the valence electrons alone occupy the valence band which tells me the valence band is ... |
Is the valence band neutral? |
Take the reaction:
$$ (1) \; A+B \leftarrow \rightarrow X + Y, \; K_1=\frac{[X][Y]}{[A][B]} $$
Now assume that X isomerizes to Z according to:
$$ (2) \; X \leftarrow \rightarrow Z, \; K_2=\frac{[Z]}{[X]} $$
We can then add the equations to obtain:
$$ (3) \; A+B \leftarrow \rightarrow Z + Y, \; K_3=K_1K_2=\frac{[Z]... |
What are these lab parts / components? |
Are there any chemistry spreadsheet-like software that:
- Generates 2D structure for the entered compounds (based on name or SMILES)
- Easy to search and create customized reports (such as similarity search)
that preferably runs on linux and is not too expensive?
I'm aware of [ICM Chemist][1] and [JChem for... |
Chemistry Spreadsheet Software? |
Take the reaction:
$$ (1) \; \ce{A + B <=>X + Y}, \; K_1=\frac{[X][Y]}{[A][B]} $$
Now assume that X isomerizes to Z according to:
$$ (2) \; \ce{X <=> Z}, \; K_2=\frac{[Z]}{[X]} $$
We can then add the equations to obtain:
$$ (3) \; \ce{A + B <=> Z + Y}, \; K_3=K_1K_2=\frac{[Z][Y]}{[A][B]} $$
It's pretty easy to sh... |
I want to do some experiments on enantiomers. As it involves more calculations of potential energy surfaces, I would like to do this experiment on a simple enantiomer. For example CHBrClF. But this is in liquid form I think. I need an enantiomer sample in the POWDER form. Can anyone suggest a simple sample? Either I ca... |
what is the simple enantiomer in the powder form that one can get? |
I'm certain that I misunderstand this law. It states that:
$$I = I_o e^{-kb} $$
and after rearranging:
$$ A = ln{I_o}-lnI $$
where $A$ stands for absorbance.
1) Does is mean that when the intensity of the exiting light is very low than the absorbance is extremely high?
2) But from the graphs in my t... |
I'm certain that I misunderstand this law. It states that:
$$I = I_o e^{-kb} $$
and after rearranging:
$$ A = ln{I_o}-lnI $$
where $A$ stands for absorbance.
1) Does is mean that when the intensity of the exiting light is very low than the absorbance is extremely high?
2) But from the graphs in my t... |
Enantiomorphs are non-superposable mirror images (all signs of one coordinate axis reversed). What is the maximum enantiomeric divergence possible? If you have a quantitatively negligible chiral divergence, there is nearly no quantitative difference to be realized in calculation or measurement. BTW, the maximum ene... |
![enter image description here][1]
[1]: https://i.stack.imgur.com/hPwbx.png
AL2O3 is a non-polar stationary phase, therefore if the molecule is also non-polar it would display high adsorption to the stationary phase, and therefore a smaller Rf value.
the answer is (a)
isnt (a) polar ??
wouldnt th... |
When two small 2D carbon platelets are pushed into proximity, why do they release edge attached molecules and then bond C to C? |
In fact $Cu$ don't release electron, only $Zn$ does. For the usual explanation see [this wikipedia article](http://en.wikipedia.org/wiki/Lemon_battery), I will try to explain it in other words to make it much easier.
----------
One important thing that you should know is that energy comes from metal not from ... |
Yama Cold Brew Tower: what are these lab parts / components? |
When two small 2D carbon platelets are pushed into proximity, why do they release the edge attached molecule (maybe O) and then bond C to C?
I think the answer I seek would address the relative difference in bond strengths, and what forces are involved to remove attached molecules, probably Oxygen. .....
BACKGR... |
Why does C=C bond replace C-O bond when two graphite platelets are rubbed against each other edge on edge? |
I've modelled the iso-surface of the highest occupied molecular orbital of a molecule with DFT in Gaussian.If I were to model the iso-surface of the molecular orbital of the singlet and triplet excited states, how would I do that?Using tdDFT, I've already calculated the excitation energy of both the triplet and singlet... |
I understand that most acids are weak acids, i.e. they do not fully disassociate in solution. However, certain acids, such as H2SO4 do. I have been unable to found out what the defining characteristic is that differentiates strong acids from weak ones.
For example, HCl is strong, yet both HF and HBr are weak (even t... |
Why do only certainly acids disassociate in water? |
**THE STORY:**
A common example used to illustrate the limitations of restricted Hartree-Fock (RHF) theory is the H$_2$ dissociation energy ($D_e$) curves. RHF enforces electrons to be paired into spin orbitals, $\chi$, or two spatial orbitals $\phi$ with the same set of spatial coordinates $\mathbf{r}$ but a diffe... |
I understand that most acids are weak acids, i.e. they do not fully disassociate in solution. However, certain acids, such as $\ce{H2SO4}$, do. I have been unable to find out what the defining characteristic is that differentiates strong acids from weak ones.
For example, HCl is strong, yet both HF and HBr are weak ... |
Why do only certain acids disassociate in water? |
For most of the metals have a look at [Optical properties of the metals Al, Co, Cu, Au, Fe, Pb, Ni, Pd, Pt, Ag, Ti, and W in the infrared and far infrared Applied Optics, Vol. 22, Issue 7, pp. 1099-1119 (1983)](http://www.opticsinfobase.org/ao/abstract.cfm?id=26571). You will find something like this:
![enter image ... |
**The Story:**
Reaction pathways can be difficult things to deal with using electronic structure methods. Intrinsic reaction coordinates (IRCs) can be determined a number of ways (a discussion of these methods lie way outside the scope of this post). Suffice to say, the reaction pathway is an 'energy' pathway of r... |
**The Story:**
Reaction pathways can be difficult things to deal with using electronic structure methods. Intrinsic reaction coordinates (IRCs) can be determined a number of ways (a discussion of these methods lie way outside the scope of this post). Suffice to say, the reaction pathway is an 'energy' pathway of r... |
**The Story:**
Reaction pathways can be difficult things to deal with using electronic structure methods. Intrinsic reaction coordinates (IRCs) can be determined a number of ways (a discussion of these methods lie way outside the scope of this post). Suffice to say, the reaction pathway is an 'energy' pathway of r... |
I tried to google this but 'element' as a programming term complicated the search.
I'm looking for a site or article that covers how one would find each element in nature, in its most abundant form. For example, what's the best natural source/form of Sulfur? Beryllium? Tugsten? etc.
Any help is appreciated. |
CH2CH2(g) + H2(g) ---> CH3CH3(g)
Using this table: http://www.kentchemistry.com/images/links/Kinetics/TB08_003.GIF
C-C enthalpy = 348 kJ/mol
C-H enthalpy = 413 kJ/mol
H-H enthalpy = 436 kJ/mol
The way I see it, H-H has to break, C-C has to break, and then two C-H bonds have to form.
(Units ... |
What is the energy change of ethene reacting with hydrogen gas? |
$\ce{CH2CH2(g) + H2(g) -> CH3CH3(g)}$
Using this table: http://www.kentchemistry.com/images/links/Kinetics/TB08_003.GIF
C-C enthalpy = 348 kJ/mol
C-H enthalpy = 413 kJ/mol
H-H enthalpy = 436 kJ/mol
The way I see it, H-H has to break, C-C has to break, and then two C-H bonds have to form.
(U... |
Are there any approximate relationships between the (static) dielectric constant of a liquid and properties of the individual molecules?
For example, suppose I know the polarizability and dipole moment of a molecule, as well as it's density in the liquid phase. Can I estimate the dielectric constant of the liquid fr... |
How to estimate the dielectric constant of a liquid? |
$\ce{CH2CH2(g) + H2(g) -> CH3CH3(g)}$
Using this table, source: http://www.kentchemistry.com/images/links/Kinetics/TB08_003.GIF
![http://www.kentchemistry.com/images/links/Kinetics/TB08_003.GIF][1]
> C-C enthalpy = 348 kJ/mol
> C-H enthalpy = 413 kJ/mol
> H-H enthalpy = 436 kJ/mol
The way I s... |
I had read some where that the water we drink should have less surface tensions and in glasses the surface tension is high, but in burbot the surface tension is low, my question is in how much time the surface tension changes? I mean that there was water in a glass but I put it into a burbot in how much time will the s... |
I had read some where that the water we drink should have less surface tensions and in glasses the surface tension is high, but in lota the surface tension is low, my question is in how much time the surface tension changes? I mean that there was water in a glass but I put it into a lota in how much time will the surfa... |
Knowing very little about the nature of water, wondering how it might behave at the centre of a planet or centre of an another massive gravitational body.
Could water take such pressures or might it break into separate hydrogen and oxygen to find something more accommodating for the pressure exerted, if such atmosp... |
What happens to water under high pressures without possibility of escape? |
In air how much CO2 would be required to prevent a match to light or a butane lighter to work?
I have a basement office that is unusable because of an apparent lack of Oxygen, currently it is my guess that the oxygen is being displaced by CO2.
A bit research suggests that it would take a reduction to around 14% fo... |
How much Carbon Dioxide would be required to prevent ignition? |
In air, how much CO2 would be required to prevent a match to light or a butane lighter to work?
I have a basement office that is unusable because of an apparent lack of Oxygen, currently it is my guess that the oxygen is being displaced by CO2.
A bit research suggests that it would take a reduction to around 1... |
The IRC algorithm usually follows the gradient from TS to product state B and by definition has to go always downhill in energy. In best case, it treats the Potential Energy Surface (PES) around the given point as quadratic and just integrates Newtonian equation of motion and does it until it reaches **local** minimum.... |
How much Carbon Dioxide would be required to displace enough oxygen to prevent ignition? |
Branched chain molecules have lower boiling point than straight chain molecules because branched chain molecules have a smaller surface area where they can be attracted by other molecules. Then, why Isodecane (a branched chain molecule) has a higher boiling point than Decane (a straight chain molecule)? |
Why Isodecane (B.P.: 327 *C) has a higher boiling point than decane (B.P.: 174.1 *C)? |
I am a bit confused 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 Al2O3 to a value lower then would be expected with perfect ionic bonding so does it decrease or increase bond strength, please explain?? |
Does covalent character increase or decrease bond strength? |
Actually it is not necessary to dig deep into quantum mechanics. There are several reasons why noble gasses are stable (as gasses at room temperature).
First of all, there is the obvious full valence shell.
Trend in the periodic table make clear that the charge of the nucleus grows from left to right in every peri... |
The parameter you are asking about is called the [Minimum Oxygen Concentration][1] (MOC), and is a measurement of the minimum amount of oxygen present in air to propagate a flame. The amount depends on the fuel being burned, and varies from about 4% for hydrogen to about 18% for some solid combustibles.
Let us consi... |
The parameter you are asking about is called the [Minimum Oxygen Concentration][1] (MOC), and is a measurement of the minimum amount of oxygen present in air to propagate a flame. The amount depends on the fuel being burned, and varies from about 4% for hydrogen to about 18% for some solid combustibles.
Let us consi... |
What exactly does the excitation spectrum tell us about a sample in Florescence Spectroscopy, what information does it tell us? I know that we will get an output of concentration vs intensity but that's it. |
**Disclaimer**: I have very limited knowledge of chemistry
My problem is the following: I have motorcycle part made from some sort of [Aluminium alloy](http://en.wikipedia.org/wiki/Aluminium_alloy) - most probably 6005, 6061-T6 or 7005. And inside of this **aluminium part** there is **steel part** which is simply **... |
In air, how much $CO_{2}$ would be required to prevent a match to light or a butane lighter to work?
I have a basement office that is unusable because of an apparent lack of Oxygen, currently it is my guess that the oxygen is being displaced by $CO_{2}$ .
A bit research suggests that it would take a reduction ... |
London Dispersion Forces are present in all either polar or non polar molecules. Molecules also exhibiting Dipole-Dipole Interactions (in addition to the LDP) must have stronger forces of attraction than those molecules which exhibit only London Dispersion Forces.
Then, why Tetra chloro methane (also called Carbon tet... |
Why Tetrachloromethane has a higher boiling point than Trichloromethane? |
Is Diethyl ether (also known as ethyl ether) a polar molecule? What type of intermolecular forces dominate it? Dipole-Dipole Interactions, London Dispersion Forces or Hydrogen Bonding? Please Explain. |
What type of Inter molecular forces will dominate Diethyl ether? |
What type of intermolecular forces will dominate Diethyl ether? |
In a book about electrochemistry the situation of a cell is described of which one half cell has an "undefined thermodynamic potential" as no redox couple exists:
$$
Pt/Cu^{2+}\ (0.01\ M),\ Cd^{2+}\ (0.01\ M),\ H_2SO_4\ (1\ M)
$$
Estimating the potential where reduction of Cu sets in by thermodynamic data when ... |
How long burned tobacco smoke remain toxic? |
How will the amount of each element change if the pressure is increased?
My guess is that the equilibrium will shift to the left, because the right side has 1 gas molecule. I know my solution contradicts with La Chateliers principles, but there is no gas on the left. So how will the the amount of the elements on the ... |
We know that for strong acids with a 1:1 mole ratio between all particles involved are suitable for use with the aforementioned formula for titration problems. I want to know the limits on this formula, that is:
Consider if we had H2SO4(aq) + 2HCl(aq) = 2H2O(l) + SO2(aq) + 2Cl-(aq)
Since the moles of H+ = moles o... |
What's the mechanism for the oxidation of primary alcohol to carboxylic acid with HNO3? |
$$\ce{CaCO3(s) <=> CaO(s) + CO2(g)}$$
How will the amount of each element change if the pressure is increased?
My guess is that the equilibrium will shift to the left, because the right side has 1 gas molecule. I know my solution contradicts with La Chateliers principles, but there is no gas on the left. So how ... |
How does equilibrium change when the products are solid and gas? |
lets say we increased the excitation wavelength higher than it should be, what effect would this have on the sensitivity on our analysis, or changing the emission wavelength to a higher value than it would be.
My guess is that the higher wavelength leads to a lower frequency and so lowers the sensitivity but I have no... |
Wood countertops are frequently sealed, when a non-hardening, food-safe finish is desired, with some [magic cocktail of waxes and oils][1]. Typical components might include [mineral oil][2], [beeswax][3], and [carnauba wax][4], mixed in some unspecified ratio and then sold at premium prices.
Not being content with p... |
Wood countertops are frequently sealed, when a non-hardening, food-safe finish is desired, with some [magic cocktail of waxes and oils][1]. Typical components might include [mineral oil][2], [beeswax][3], and [carnauba wax][4], mixed in some unspecified ratio and then sold at premium prices.
Not being content paying... |
Why do certain solutes dissolved in water release heat and other solutes absorb heat? |
What is the pKa of the oxonium / hydronium / H3O+ ion? |
Although the wikipedia page on Hydronium indicates a pKa of -1.74, I noticed in the discussion of this page that the subject seems debated (cf. http://en.wikipedia.org/wiki/Talk:Hydronium#pKa.3F) since alternative (apparently more rigorous) reasoning leads to $pK_{a} = 0$ for $\ce{H3O+}$.
Also, many demonstrations... |
![enter image description here][1]
[1]: https://i.stack.imgur.com/oIRra.png
Why is the textbook answer Ca.... Why not Ca2+ ? |
We know that for strong acids with a 1:1 mole ratio between all particles involved are suitable for use with the aforementioned formula for titration problems. I want to know the limits on this formula, that is:
Consider if we had H2SO4(aq) + 2KOH(aq) --> 2H2O(l) + K2SO4(aq)
Since the moles of H+ = moles of OH- i... |
![enter image description here][1]
[1]: https://i.stack.imgur.com/oIRra.png
Why is the textbook answer $\ce{Ca}$, why not $\ce{Ca^2+}$ ? |
Flame test: Is the metal atom or the metal ion responsible for the flame colour? |
We know that for strong acids with a $1:1$ mole ratio between all particles involved are suitable for use with the aforementioned formula for titration problems. I want to know the limits on this formula, that is:
Consider if we had $$\ce{H2SO4(aq) + 2KOH(aq) -> 2H2O(l) + K2SO4(aq)}$$
Since the moles of $\ce{H+}$... |
I had read some where that in glasses the surface tension is high, but in a lota the surface tension is low.
My question how much time does the surface tension take to change? I mean that there was water in a glass but I put it into a lota in how much time will the surface tension of water change? Immediately?
Thi... |
Is there any trick to memorize the angles and sides of 7 crystal systems of crystalline solids?
1. Cubic
2. Tetragonal
3. Orthorhombic
4. Monoclinic
5. Hexagonal
6. Rhombohedral or Trigonal
7. Triclinic
|
How to memorize 7 crystal systems? |
Although the wikipedia page on Hydronium indicates a pKa of -1.74, I noticed in the discussion of this page that the subject seems debated (cf. http://en.wikipedia.org/wiki/Talk:Hydronium#pKa.3F) since alternative (apparently more rigorous) reasoning leads to $pK_{a} = 0$ for $\ce{H3O+}$.
Also, many demonstrations... |
I am studying a reaction using electronic structure methods using various software packages (ORCA,GAMESS, G09) and have found two possible transition structures between product and reactant. Both have imaginary frequencies, but each has a different energy value, frequencies and geometries. Some software coincide in the... |
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