CoffeeIsLife
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Aside from carbon, what other substances can be made "superhard"?
21 votes

Here are some compounds that have other structures, followed by their hardest structure (based on Moh's Scale). Titanium dioxide: Rutile structure or Cotunnite structure Aluminum oxide: Corundum ...

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A comprehensive list of theoretical approximations that are used in computational chemistry
19 votes

The goal of computational chemistry is to obtain the properties of a system. This is done by solving Dirac's Equations. Treating particles as point particles with mass In most computational software, ...

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What's the difference between reactant, excess reactant and limited reactant in a balanced equation?
14 votes

Suppose that you want to make a cake. You would first need to go your fridge to check whether you have the necessary ingredients to make one. So you go to your fridge. Luckily, you have all the ...

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Covalent and Ionic Bonds
13 votes

Bonds are usually used to describe how electrons are shared. "Partially ionic bonds" are polar covalent bonds. Which is not the same as saying that a compound has different types of bonds in the whole ...

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What is the nature of interstitial hydrides?
Accepted answer
10 votes

Nonstoichiometric compounds are simply compounds that cannot be represented with integer number of atoms. What the book probably is trying to say is that the hydrogen atoms do not simply fill the ...

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Why does paper turn yellow over time?
9 votes

from "Stuff Matters" by Mark Miodownik: Paper yellows with age for two reasons. If it is made from cheap low-grade mechanical pulp, it will still contain some lignin. Lignin reacts with ...

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Polarity index vs. Dipole moment
Accepted answer
8 votes

From Roger E. Schirmer "Modern Methods of Pharmaceutical Analysis": Solvents are generally ranked by polarity, but polarity is not a uniquely defined physical property of a substance. Hence the ...

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What are Lattice Points?
6 votes

There are different types of lattices. A lattice point is a point in any of these lattices. Lattices are used to describe highly ordered systems such as crystals and some supersolids. I am unsure ...

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How are N95 masks different from dust masks?
6 votes

The principle on which they depend isn't that different. This does not mean, however, that you can wear a dust mask instead of an N95. From the Review article of "Respiratory Protection" from the New ...

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Do non-English speaking countries use the same element symbols?
6 votes

Both North Korea and South Korea use the periodic table. The names, however, are different. Here is a periodic table in North Korea The title translates to "Mendeleev's atomic periodic table." The ...

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Reaction intermediates of MnO2 catalyzed H2O2 decomposition reaction
6 votes

I am adding a more recent study to complement the answer given by tschoppi. This journal addresses the kinetics and mechanism for the decompostion of $\ce{H2O2}$ on transition metal oxide surfaces. ...

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Why is it that the least reactive metals are the best electrical conductors?
6 votes

One of the reasons why non reactive metals are good conductors is that they are good at staying as metals. Most metals react with the atmosphere to form oxides. And the majority of oxides are ...

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Does a diatomic gas have one or two vibrational degrees of freedom?
5 votes

There are two ways to think about the degrees of freedom for a vibration. One of them is to think only about the number of vibrational modes. The number of vibrational modes for a linear molecule is ...

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Transiesta Electrode Run
5 votes

There is a manual available that states (page 111). TranSiesta defines the Left Electrode to be the first atoms specified in the SR .fdf file, and the Right Electrode to be the last ones. ...

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Can formaldehyde be stored at a higher temperature than room temperature?
Accepted answer
5 votes

Trimerization of formaldehyde can happen at high temperatures, but appear to require catalysts. There is a patent for synthesizing 1,3,5-trioxide at high temperature. This patent uses phosphoric acid ...

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Is there a general way to predict products of a chemical reaction
5 votes

Often times it is possible due to previous data. Trends appear and you can make deductions from such trends. Reactions may not happen at all. There may be deviations from the trends as well. The ...

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Phosphate extraction from sewage
Accepted answer
4 votes

The idea has been proposed by several journal articles and Wikipedia suggests that it is being done already. In "Phosphate fertilizer from sewage sludge ash (SSA)", Franz proposes a method ...

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Band gap of Transition Metal Dichalcogenides
4 votes

From "The indirect to direct band gap transition in multilayered MoS2 as predicted by screened hybrid density functional theory"[1]: First, in the bilayer, there is strong splitting in the ...

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How are solvents chosen in organic reactions?
4 votes

There are many factors. You have to consider the solubility of reactants since the reactants have to mix to react better. There is a solubility chart for several organic solvents. A lab that I used to ...

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How to calculate the heat released by the combustion of ethanol in excess oxygen?
Accepted answer
3 votes

It says that 2 moles of of $\ce{CH3OH}$ release $\text{1354 kJ}$. This is the same as saying that 1 mole of of $\ce{CH3OH}$ releases $\text{677 kJ}$. Here I just divided the 1354 by 2 to obtain the ...

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Solubility curve for uranium hexafluoride (in any solvent)
Accepted answer
3 votes

So far I have found that it is soluble in: Bromine Pentafluoride Chlorotrifluoroethylene Liquid Polymer, Dichlorotetrafluoroethane, Perfluorotributylamine, Perfluoroisopropyl ether, 1,2-...

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Why does ethanol have a health rating of [2] in NFPA 704 whereas methanol, which is far more toxic, has a rating of only [1]?
3 votes

I believe that the rating is dependent on toxicity tests. The acute oral toxicity LD50 value of acetone is 5800 mg/kg The acute oral toxicity LD50 value of methanol is 5628 mg/kg The acute oral ...

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What's considered a "higher" level of theory in quantum mechanics calculations?
3 votes

If you want to solely know about DFT functionals, read about Jacob's ladder of functionals. There's a good recent review of a slew of DFT functionals: http://dx.doi.org/10.1063/1.4948636 I do not ...

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Why does ammonia have sp hybridization?
3 votes

This question has been answered before. Look here: http://answers.yahoo.com/question/index?qid=20130803221208AAYOCBr If you look at the MO diagram for $\ce{NH_3}$ you'll find that the orbital which ...

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Calculating ppm of an ion in a solution
2 votes

You are wrong. Assuming that you are doing ppm in terms of mass: There are $0.0055$ grams of $\ce{Fe(NO3)2}$. Its molar mass is $179.8548$ grams/mol. Thus, you have $3.058022\!\times\! 10^{-5}$ moles. ...

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The MO and unpaired electrons
2 votes

Oxygen can exist in two states, the singlet and triplet state. The triplet state is the ground state whereas the singlet state is the higher energy state. In the triplet state the highest energy ...

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Does a red hot metal reflect light in the same way as a cold metal?
2 votes

The light that you see from hot metals is incandescence. Incandescence is caused by high temperature. The high temperature promotes electrons to higher energy levels. These electrons then relax and ...

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Solid state and packing
2 votes

An unit cell is a periodic structure. There are two types of unit cells: conventional unit cells and primitive unit cells. The conventional unit cell is the one that is used most often. Nevertheless, ...

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Diels Alder reaction with maleic anhydride. Reactivity of different dienes
Accepted answer
2 votes

a) The compound can rotate into a trans configuration that is not suitable for Diels Alder b) The compound is locked into a cis configuration that is favorable. Furthermore, a carbon group is ...

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Does increasing electronegativity imply more covalent character?
2 votes

The main force responsible for holding together covalent bonds and ionic bonds is different. Ionic bonds are held together through electrostatics. A transfer of electrons causes one atom to be ...

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