New answers tagged physical-chemistry
1
Without doubt, the previously provided answers will work well if the crystallographic model is a description in space group triclinic $P1$. However on occasion, the symmetry of the unit cell is higher and the molecule of interest is on a special position, for example a centre of inversion. As a result, the underlying .cif file need not to contain as many ...
3
The answer by porphyrin is correct and arguably the proper way to perform the transformation. But there is another / simpler way to convert between fractional and cartesian coordinates that requires a little less programming.
Provided you have the lattice vectors of the cell $\vec{a}_1$, $\vec{a}_2$, and $\vec{a}_3$ (in cartesian coordinates), you can ...
3
You can actually calculate orbital "energies" with MO theory. The resulting "energies" for $\ce{N2}$ are the following (calculated with molpro and CASSCF(10,8)/aug-cc-pVTZ):
Orbital "energies" in atomic units
orbital
energy/a.u.
1σg
-1.11
2σg
-0.99
1σu
-0.77
πu
-0.59
πg
0.29
2σu
1.22
As you can see, the "energy"...
3
OP's question is: Is the conductivity of $\ce{CaSO4}$ the difference of $\pu{7.0 \times 10^{−4} S cm−1}$ and $\pu{2.6 \times 10^{−4} S cm−1}$?
In this question, $\pu{2.6 \times 10^{−4} S cm−1}$ is the conductivity of original aqueous $\ce{Na2SO4}$ solution and $\pu{7.0 \times 10^{−4} S cm−1}$ is the conductivity of original aqueous solution when saturated ...
3
Yes, even very small particles can "stick" permanently to solid surfaces in solution just like gases or liquids. Just note that the particles have to be nanometer sized. One classical discovery, which made million dollar business in the field of chromatography is that of so-called agglomerated ion-exchange phases (Dionex).
Basically you have ...
2
Neither one of the following two might be rigorous enough from the perspective of a mathematician because of some overlap of the fields within chemistry, or by initial inspiration / interaction with fields outside chemistry. Thus I think the answer is no.
However, curricula at universities typically divide chemistry into general, inorganic, organic, ...
0
There is no good solution
Salts, silicagel, anhydrides - are all requiring some recharge later, usually with high tenperature. Which makes it unhandy, because it is another thing you have to think about.
Peltier dehumidifier - requires a large battery, and still require recharging. With electricity this time. But still after evrey use unless battery is heavy....
2
How high atomic number can go is a nuclear question. Any lump of positively-charged matter will find and bind as many electrons as it needs.
While it is true that the limiting value of Z is unknown an unpredictable, the same is not true for an outer boundary to the region of a (Z,N) or (Z,A) plane within which atomic nuclei can exist. Since an outer ...
-2
There is a similar question on StackExchange from 6 years ago (Ref 1), from which I have taken Diagram #1:
DIAGRAM #1
And a quote from the answer: "Many of the diagrams (on the internet) are different one from another - that's a tip off that s-p mixing is not something that can always be predicted in advance." Something like Diagram #2 below, ...
0
If the system is at lower pressures where the ideal gas law is close to valid, then the partial pressure of the volatile species (mole fraction times total pressure) can be used in place of the vapor pressure with the Clausius Clapeyron equation. At higher pressures, the free energy of the liquid is affected by the higher overall pressure, as is the partial ...
5
First, be aware that the order of a chemical reaction depends on its mechanism and a great deal of chemical reactions have more than one mechanism, depending on the conditions.
The traditional example for zeroth order reaction is a reaction fully dependent on a catalyst (e.g. enzymes in biochemistry).
When you have enough reactants and a scarce amount of the ...
2
Two carbon dioxide scrubbers come to mind: lithium hydroxide and soda-lime.
(https://en.wikipedia.org/wiki/Lithium_hydroxide)"Lithium hydroxide is used in breathing gas purification systems for spacecraft, submarines, and rebreathers to remove carbon dioxide from exhaled gas by producing lithium carbonate and water:
2 LiOH•H2O + CO2 → Li2CO3 + 3 H2O
or
...
13
A standard example in biochemistry are enzyme-catalyzed reactions with a single substrate (e.g. ATPase, where we ignore the second substrate, water, because it is the solvent). At low substrate concentration (low reactant concentration), the reaction is first order (actually, pseudo-first order because of the water). At high susbtrate concentration (high ...
15
I think to some extent, you can think about all zero-order reactions as "pseudo-zero-order" reactions. This is because it's not possible for a reaction to be true zero-order. How can it be that the rate of a reaction does not depend on any one of the reactants? So, anything that is zero-order means that there is some artifact in the system, or that ...
9
Zero-order kinetics can also appear in certain industrial settings. In some steel strip annealing processes where improved bendability of the product is required, steam is applied to decarburize the steel near the surfaces of the strip according to the reaction
$\ce{C(s) + H2O(g) -> CO(g) +H2(g)}$
The decarburization process requires carbon to diffuse out ...
7
The best example of a zero-order reaction is the combustion of a candle. If the candle weighs $m_o$ grams at the beginning, and $m$ at any time afterwards, and if $a$ grams of it are burned per minute, the reaction rate $r$ is constant from the very beginning to the end of the candle, and it is : $r = dm/dt = a$ in grams per minute. The integrated rate law ...
3
As it has been pointed out, molecular oxygen is paramagnetic. It is exceptional in that. Usually, you require either a transition metal ion, or a lanthanide ion, or a radical, for a molecule to be paramagnetic.
For most other molecules, including as far as I can tell the fuels you mention, you can safely assume that they are diamagnetic. Paramagnetism is ...
1
Okay, so I managed to get a solution without too many equations by making the right approximations.
First with your expressions:
$\ce{K_{sp} = [Mg^2+][NH_4^+][PO_4^3-]}$
$\ce{K_{sp} = (S)(0.1)(S-x})$
Here we want to find S-x which is $\ce{[PO_4^3-]_{eq}}$. To do this, I did the following:
$\ce{\frac{[PO_4^3-][H+]}{[HPO_4^2-]}=K_{a3} = 10^{-12.4}}$
Assuming $\...
1
Let's consider an example of your galvanic cell : the Daniell cell, made of a zinc anode ($\ce{Zn}$) and a copper cathode ($\ce{Cu}$). When zinc $\ce{Zn}$ is in contact with water, it "prefers" being transformed into the cation $\ce{Zn^{2+}}$ in order to be dissolved in water. In your language, you say that they are more "comfortable" in ...
-1
I was also confused at this same problem, but what I found out is that there are 2 possible explanations for this conundrum:
Entropy causes everything to become more disordered, and so ionic compounds will dissolve to increase entropy.
Each ion can participate in multiple ion-dipole interactions when dissolved, and these multiple ion-dipole interactions ...
2
Thermodynamics courses usually start by calculating amounts of heat and amounts of work enterring a container. And the work is $\pu{p\Delta V}$. No mention of concentration ! Just the pressure. Afterwards, enthalpy is introduced, then gas chemistry is developed, always using pressures. Equilibrium constants are then introduced, always with gases and ...
6
I've only basic training in chemistry, since my competences are in Electrical Engineering, but I'd like to tackle your question from another angle.
I'm assuming your question is sort of an X-Y problem and you are not really interested in increasing the efficiency of an actual lemon-based cell.
From an engineering POV, what you want from a power source is, ...
2
When you are implying reaction quotient, you should use $Q$ instead of $K$. As $Q$ is defined at any concentrations other than equilibrium.
When you are changing $[\ce{A}]$ and $[\ce{B}]$, $[\ce{A2B}]$ may change also, which you have neglected.
From the given data, the change in rate of reaction cannot be calculated for the reason you have pointed out in ...
14
Yes, you can have same the electrolyte and a pair of two different metals, but the key point is that if you wish to increase voltage difference, you need to connect them in series and use separate containers for each pair, and of course each pair must be connected. Your postulate in the comment is correct. If we use a large bucket, only the pair connected to ...
18
Yes, you could have multiple electrodes in the same electrolyte, but to some extent, that would short-circuit the battery. For example, if you stack copper and silver coins with blotting paper (bp) between them, in the order:
Cu bp Ag Cu bp Ag ... Cu bp Ag and immerse the whole in an electrolyte, rather than just wetting each piece of blotting paper, some of ...
5
the Larmor frequencies of A and X are not the same despite being homonuclear (already called 'AX', chemical shift very different, Larmor frequency also differ), so the states should have different energy
Yes, that is precisely correct, so the two states $|\alpha\beta\rangle$ and $|\beta\alpha\rangle$ do not have the same energy. More formally, the ...
1
I'll continue after volume of $\ce H_2O$ vapours = $0.5 ml$
Vapour pressure is equal to the partial pressure of water in gas phase.
$P_{\ce H_2O} = P_{total}$ × mole fraction of $\ce H_2O$
Where $P_{total}$ is $1 atm$ and mole fraction = $0.5/25$
So $$P_{\ce H_2O} = \frac{1}{50} atm = \frac{760}{50} mm Hg$$
Now for the solution of non volatile solute $A$
...
1
Who says it's exponential? That the reaction is first-order?
If the rate is "too high" early in the reaction when concentration is high, but "too low" later on when concentration is low, that indicates you have a higher concentration dependence than the first-order you assumed when you expected an exponential curve.
If we were to assume ...
-4
Yes, one can calculate the specific heat capacity of the compound from its constituent elements that is just some of its constituent element's specific heat capacity. As it is known that specific heats of elements remain unchanged when they enter into compounds. However, the density/volume/mass may change and so the heat capacity.
4
The first representation is ball and stick, because atoms represented as spheres, and bonds in rod-like shape. The lower illustration is an example of stick, where atoms and bonds share the visualization as a stick. The question is not limited to the visualization of coordination compounds, nor the file type read by the program. If you use Avogadro 1.2.0 (e....
5
TL;DR: The data from the assignment is correct.
You confused yourself by assigning $h_i^2 + k_i^2 + l_i^2$ to the ratio of $\sin^2\theta_i$ values, and keep in mind $(100)$ might be absent.
First, let's get bold and assume that we are indexing a cubic system.
This is usually the first step in analytical indexing, plus it's an extremely common system for ...
23
To convert this into a generic linear algebra problem you'd rewrite it in the form $Ax=b$ where $A$ is a matrix of stoichiometric coefficients of size $m \times n$; $x$ is a vector of length n of unknown fitting parameters (the heats you want to determine) and $b$ a known vector of length n.
For the example problem the set of equations can be written in ...
1
Which of these functional groups is soluble in aqueous HCl and/or NaOH?
Functional groups don't have solubility. Their presence in a compound, however, can have an effect on solubility.
My approach before was this : Esters do not dissolve in cold aqueous bases or acids, nor do amides or alcohols. Amines dissolve in aqueous acids. Phenols and Carboxylic ...
2
The answer by A.K. is eminently reasonable, but I wondered if stability constants were available. I quote from the summary of Ref. 1 :
The solubility of silver chloride in concentrated solutions of various
chlorides was determined mainly at 25°.
The solubility is nearly doubled in going from o° to 25°, the rate of increase above and below 25° being nearly ...
6
Two water drops 1 mm apart do not attract each other, if I omit gravity and electrostatic charges. Are they hydrophobic ? No, they are not. The relevant intermolecular forces are contact ones, decreasing very fast with high power order of distance.
Water molecules in a gaseous phase have still strong attraction during their collisions, what reflects in vapor ...
4
Yes. The universal condition for equilibrium is that, given the current constraints on the system, no further spontaneous change can take place. I.e., that the entropy of the universe (system + surroundings) is maximized.
At constant temperature and pressure, a maximization of the entropy of the universe corresponds to a minimization of the Gibbs free ...
1
tl;dr– Hydrophobic-water would be water that doesn't significantly cohere to itself. So, water's hydrophobic when it wouldn't form a condensed-phase (e.g., if it boils and preferentially exists as a gas at equilibrium). Can't have hydrophobic-water in an equilibrium-preferred condensed-phase, as a condensed-phase means that the material's sticking to ...
25
You can't make hydrophobic water molecules. You can, however, make hydrophobic droplets containing mostly water. They are not made of pure water, but are coated with a substance that remains on the surface of the water droplet and changes the properties of the surface.
Here is an example of making such a hydrophobic drop: https://www.youtube.com/watch?v=...
10
Water cannot be made hydrophobic. Water drops can be set to act like if water were hydrophobic, but it would not be pure water anymore.
The drop surface can be made hydrophobic by hydrophobic liquid, film or dust. See the links in the Karsten's answer.
A dirty trick could be electrostatic charging of separated water drops, e.g. in the Kelvin_water_dropper, ...
2
Consider the partial pressures separately. If you answer these questions you have your own solution.
Oxygen does not condense, may be deemed an ideal gas. What does halving the volume do to its partial pressure? (We assume that exactly half the volume, 50 ml vs 100 ml, is available because we neglect the liquid volume in this problem.)
Water can condense, ...
2
According to IUPAC Goldbook:
A chemical species that behaves both as an acid and as a base is called amphoteric. This property depends upon the medium in which the species is investigated: $\ce{H2SO4}$ is an acid when studied in water, but becomes amphoteric in superacids.
Most common example for amphoteric compound is water, which can act either as an ...
3
According to Nickel Metal Hydride (NiMH): Handbook and Application Manual of Energizer Nical Metal Hydride:
The nickel-metal hydride battery chemistry is a hybrid of the proven positive electrode chemistry of the sealed nickel-cadmium battery with the energy storage features of metal alloys developed for advanced hydrogen energy storage concepts. This ...
3
The cathode is made of $\ce{NiOOH}$ when the cell is new. This can also be written $\ce{NiO(OH)}$,where the oxidation degree of $\ce{Ni(III)}$ is more evident. The cathode is made of $\ce{Ni(OH)2}$ when the cell is discharged. Whatever the nature of the anode (cadmium, hydrogen, or any other material), the cathode is working according to the equation $$\ce{...
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