Most Popular
1500 questions
18
votes
4 answers
Is enthalpy additive in mixing?
When mixing two fluids of different composition at constant pressure when no heat can escape, is the enthalpy additive?
If not, how to compute the enthalpy of the mixture resulting from mixing two fluids with given composition after equilibrium is…
Arnold Neumaier
- 461
- 3
- 10
18
votes
3 answers
Does an irreversible reaction have an equilbrium between reactants and products?
Retrospective analysis 2/13/2017 -- The barium sulfate example is a poor choice. Equilibrium equations should really be defined using activities, and the activity of solid barium sulfate is by definition 1.
A previous question, Is every chemical…
MaxW
- 22,242
- 2
- 36
- 80
18
votes
5 answers
Is every chemical reaction in equilibrium?
I read that every chemical reaction is theoretically in equilibrium in an old textbook. If this is true how can a reaction be one way?
user109987
- 191
- 1
- 1
- 6
18
votes
2 answers
Do bare protons exist, even transiently, in aqueous solution?
Generally $\ce{H^+}$ ions in water remain in the form of hydronium ions ($\ce{H3O+}$), and not as "free" aqueous protons, as far as I've been taught.
My question: is this always the case, even when considering dynamics at extremely short time…
Sangkha Borah
- 419
- 2
- 7
18
votes
2 answers
Why do chalcogens (Group VI) stink so badly?
For more fun with Dr. Derek Lowe, see this for a primer: Things I Won't Work With - Carbon Diselenide. The short of it is that we carbon-based life forms generally like oxygen. However, move just one row down in the group, to sulfur, and things…
KeithS
- 6,634
- 1
- 30
- 39
18
votes
3 answers
Why are acids usually depicted in fiction as green?
In cartoons, etc., acid is generally shown as vividly green, as in this scene from the Simpsons:
We even have the colour "acid green".
But when I used to use acids in chemistry class, they weren't bright poisonous green. They were mostly…
Au101
- 901
- 3
- 9
- 17
18
votes
2 answers
Why do all radioactive decay series terminate at lead?
Thorium series:
Uranium series:
Actinium series:
Why do all the radioactive decay series terminate at lead isotope? Why not hydrogen?
(All pictures were taken from Wikipedia.)
Nilay Ghosh
- 25,509
- 26
- 91
- 197
18
votes
1 answer
How does VB theory explain the Si-O-Si bond angles in SiO2?
Silicon dioxide has a huge variety of structures. Most of them are built up from connected $\ce{SiO4}$ units — the $\ce{O–Si–O}$ angle is $109.5°$, accordingly. The VB/hybridization approach to this tetrahedron would consequently assign $4\text{…
Corundum
- 730
- 2
- 7
- 21
18
votes
1 answer
Formation of a stable hydrate
Question: Which of the following does not form a stable hydrate?
I think they mean nucleophilic addition of water. For compound (C), on reaction with water, the product formed is
The product has lesser bond angle strain than the reactant.…
Aditya Dev
- 7,786
- 16
- 67
- 113
18
votes
1 answer
Why is sulfur hexafluoride more stable than selenium or tellurium hexafluoride?
I was just reading about p Block elements from two different books. Both books say that $\ce{SF6}$ is extremely stable in 16th group due to steric reasons but my question is why is it more stable than $\ce{SeF6}$ and $\ce{TeF6}$ when $\ce{S}$ is…
Quark
- 946
- 1
- 9
- 27
18
votes
2 answers
By what reaction does (–)-sparteine decompose in ambient conditions?
In its pure form (–)-sparteine is an only-slightly-yellow clear, viscous liquid. Yet, after only a week of being kept in dry, normal atmosphere (in a round bottom flask covered by a septa), some of it reacts with something to form a sticky,…
Brad
- 181
- 4
18
votes
2 answers
How to convert from spin orbitals to spatial orbitals in the Hartree-Fock approximation?
I need to calculate some of the more complicated self-energy terms from chapter 7 of Szabo and Ostlund's "Modern Quantum Chemistry", and I'm having trouble converting summations from spin orbitals to spatial orbitals.
Exercise 2.18 (page 85) is…
mszep
- 438
- 2
- 9
18
votes
1 answer
How can a group be both a good nucleophile and a good leaving group?
I'm reading about $\:\mathrm{S_N1}$ and $\:\mathrm{S_N2}$ reaction mechanisms, and I have a few questions.
My book has a couple of tables, one lists a bunch of substances grouped as good, moderate and poor nucleophiles. Among the good are $\ce{Br-}$…
user1160
18
votes
2 answers
Saturated vs unsaturated fats - Structure in relation to room temperature state?
I'm sure most of us have heard that saturated fats are solid at room temperature, and unsaturated fats are liquid at room temperature. I'm wondering how this relates to their chemical structure -- saturated fats contain only single bonds between…
yelx
- 281
- 1
- 2
- 6
18
votes
6 answers
Why does the two-electron exchange integral in Hartree-Fock theory have positive values?
In Section 2.3.6 of Szabo & Ostlund's Modern Quantum Chemistry, the exchange integral has the form of
$$\int \mathrm{d}\mathbf{r}_1\,\mathrm{d}\mathbf{r}_2\, \psi_a^*(\mathbf{r}_1)
\psi_b(\mathbf{r}_1)\frac{1}{r_{12}}
\psi^*_a(\mathbf{r}_2)…
Molec
- 181
- 1
- 6