DavePhD
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Is delta H a state function?
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$\Delta H$ is a function of two states, the initial state and the final state. For a given final state, there can be infinite $\Delta H$ values depending upon what the inital state was. For a ...

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Can I make a buffer from two different weak acids or bases?
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8 votes

Yes, having multiple weak acids and/or bases having different pKa values would give buffering capacity in more than one pH range, or over a greater pK range. There is a term "universal buffer" ...

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How to know it when I see a covalent network?
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A good source of information on this topic is the website Tetrahedra of Structure, Bonding & Material Type, from which the above image is taken. An extreme example of the metal corner should be ...

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Why do copper (II) complexes contain so many valence electrons?
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I'll address $\ce{[Cu(NH3)4(H2O)2]++}$, but the reason is similar for $\ce{[Cu(NH3)4]++}$ The 9 d-electrons in the complex are in non-bonding and antibonding orbitals. See pages 6-9 of Ligand Field ...

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How quickly does ethanol evaporate?
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Certainly water and ethanol and all mixtures thereof will completely evaporate without boiling given enough time. Water and ethanol form a postive azeotrope that is 95.6% ethanol and 4.4% water and ...

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What is the reason behind choosing the specific elements used for the synthesis of heavier elements?
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There are different strategies for synthesizing superheavy elements. Two of the main strategies are referred to as "hot fusion" and "cold fusion". The first two reactions are good examples of the "...

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It is said that atoms cannot be created. If so, then how did atoms get created after the Big Bang?
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Atoms can be created and destroyed. For example, in nuclear fusion two or more atoms make one atom. In nuclear fission, one atom makes two or more atoms. how did the atoms form after the Big Bang?...

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How could a scientist from the 1800s to the 1920s run spectroscopy of chemicals?
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Light from a flame, the sun, or a star, was passed though a narrow slit, then directed through a prism (F) and observed. The prism is rotatable about a vertical axis to adjust the wavelength range ...

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What is the difference between the Joule and Joule–Thomson coefficients?
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7 votes

The Joule coefficient is $$\left(\frac{\partial T}{\partial V}\right)_U$$ Experimentally, Joule attempted to measure this value by expanding gas into an evacuated, insulated container, thus ensuring $...

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Why is it necessary to consider infinitesimal changes in p,V,T for H,U and G given that they're state functions?
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7 votes

It is important to make clear any requirement that a variable be constant for each equation you write. To go from $$\mathrm{d}G = V\,\mathrm{d}p - S\,\mathrm{d}T$$ to $$\mathrm{d}G = V\,\mathrm{...

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Does a neutral dimercury molecule exist?
7 votes

Yes, $\ce{Hg2}$ has a bond length of $\pu{0.334nm}$ and a dissociation energy of $\pu{7.5 kJ/mol}$. See Mercury Handbook: Chemistry, Applications and Environmental Impact at page 10. and Mass ...

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Reactivity of different isomers of N2F2
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According to Dinitrogen Difluoride Chemistry Inorg. Chem., 2010, 49 (15), pp 6823–6833: This increased reactivity of the cis-isomer can be readily explained. In both $\ce{N2F2}$ isomers, each ...

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Are nuclear spin isomers "allotropes"?
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Some peer review journal articles and an India high school textbook and various study guides do refer to the spin isomers as allotropes. There are physical differences such as different heat ...

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What is the structure of trifluoromethanesulfonic acid in the gas phase?
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Has the structure of trifluoromethanesulfonic acid or a structurally strongly related acid been studied in the gas phase? (Please provide a reference) Yes. See Gas Phase Structure of Methyl ...

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Why does cobalt have a higher atomic mass than nickel?
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Protons in each nucleus repel each other electrostatically. As atomic number increases, there is more repulsion and an increasing advantage of spreading out the protons with neutrons. Calcium-40 is ...

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Are any bonds broken when NO2 becomes N2O4?
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7 votes

No bonds are broken, but there are several isomers of N2O4. The unpaired electron can be on either the N or the O, for each NO2 molecule. The long bond between the monomers involves these two ...

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Is there any notion of pH out of solution?
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7 votes

The IUPAC definition of pH is: The quantity pH is defined in terms of the activity of hydrogen(1+) ions (hydrogen ions) in solution: $pH = − lg [a(H^+)] = − lg [m(H^+) γ_m (H^+) / m^⦵]$ where a$(\ce{...

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Common ion effect and acids
7 votes

The $\ce{Br-}$ would make less $\ce{HBr}$ dissociate, But $\ce{HBr}$ is such a strong acid ($\mathrm{pKa}$ is $\mathrm{-9}$) that still only a trivial amount would be molecular.

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Why will CuSO4 solution be acidic?
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7 votes

Because the second pKa of sulfuric acid is weak, sulfate withdraws protons from water. Therefore, the contribution of sulfate alone is to make the solution slightly more basic than pH 7. However, as ...

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Stability of isomers of N4O
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7 votes

From The Nitrosyl Azide Potential Energy Hypersurface: A High-Energy-Density Boom or Bust? J. Am. Chem. Soc. 1996, 118, 4860-4870 : [Abstract] ...While the ring isomer is predicted to be the most ...

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At what temperature do complex hydrocarbons become ashes?
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What happens depends whether it is being heated in the presence or absence of oxygen. For example, in the manufacture of coke (mostly carbon), coal is heated without oxygen and from Coke Production ...

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When disqualifying trans fat, are we qualifying cis-fat as healthy?
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7 votes

If cis is what's naturally found, by default it's unsaturated fat isn't it? Both cis and trans are unsaturated. "Unsaturated" means having at least one C-C bond that is not a single bond (but ...

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Would C bond with H or D?
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7 votes

C-H would be the weakest bond, then C-D, then C-T would be the strongest. This is due to the zero point energy of the bond and the fact the zero point energy is proportional to: $$\sqrt{\frac{m_C + ...

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Is tetraammine dichloro cobalt (III) an optically active compound?
7 votes

The 6 ligands are at the 6 vertices of an octahedron. There will be cis and trans isomers, but neither isomer is optically active. For the trans isomer, there will be a central axis containing Cl-Co-...

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Methanol skin exposure serious or not?
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"[A] factory worker who spilled a gallon of methanol down his trouser leg, was dizzy on the following day, took a short nap, and woke up total blind" Biochemical aspects of Methanol Poisoning, ...

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Is there a name for the opposite reaction to the dissolution?
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7 votes

Effervescence if there are bubbles and Degasification more generally speaking. There is also the term outgassing, but that term is broader than just gas coming out of liquid solution.

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London dispersion forces and distance relationship
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7 votes

One somewhat simplified way of looking at it is that the London dispersion forces are a dipole-dipole interactions. The interaction between two dipoles depends upon the relative orientation of the ...

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What effects would an electron in the nucleus have?
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An electron being at/in the nucleus results in the Fermi Contact Interaction. This interaction can be observed experimentally through NMR, EPR, and electron capture. In NMR of paramagnetic ...

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Where does the Fe(III) ion go?
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7 votes

In solution, the iron(III) will be hexaaqua iron(III), 6 water molecules coordinating the iron ion, with the oxygen atoms being at the vertices of an octahedron. Hexaaqua iron(III) has a high spin d5 ...

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If the hydroxide ion is such a poor leaving group then why does water dissociate?
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7 votes

Only 1 in 10,000,000 water molecules dissociate. HI, HBr and HCl fully dissociate, and I-, Br-, and Cl- and are much better leaving groups.

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