# Tag Info

29

Your realisation is correct and something chemistry teachers try to hammer into their students’ heads time and time again (and yet, the point is still often lost): Catalysts will never change the thermodynamics of a reaction. They only ease the path of the reaction. Forward and backward reactions will be accelerated equivalently. So what is the benefit of ...

20

The function of pyridine is actually not so simple and not so easy to notice at first glance. There is a fundamental reason why pyridine is used to promote the acylation reaction, which is that it can act as a catalyst. Despite its basicity and the subsequent formation of its chlorhydrate salt after the tosylation reaction, pyridine is also an excellent ...

17

In short, a catalyst does participate in a chemical reaction the rate of which it increases, it just do so in a somewhat tricky way so that it does not appear in the overall reaction equation. Wikipedia article on catalysis provides a concise explanation of why this is the case: Catalysts generally react with one or more reactants to form intermediates ...

16

This is a rather interesting question because these names actually refer to classes of reactions (specific to certain reagents and products), and aren't constrained by specific proportions of substances or even the identity of these substances. $\hspace{4cm}$ A Rosenmund catalyst is used to reduce acyl chlorides to their corresponding aldehydes, and is ...

15

$\ce{Pd}$ can dissociate $\ce{H2}$ because the resulting $\ce{Pd-H}$ bonds are more stable than the starting $\ce{H2}$. But the reason why $\ce{Pd}$ is so good at dissociating $\ce{H2}$ is related to the energy barrier to bond formation. The dissociation of $\ce{H2}$ on a $\ce{Pd}$ surface (and on $\ce{Pt}$ and maybe several other metals) has no barrier. So ...

14

Step one: trap $\ce{CO2}$. This can be done using specially selected amines, like triethanolamine. Aminosilicones (a common chemical used in hair conditioner), can also do this. Step two: release trapped $\ce{CO2}$. In case of triethanolamine you'll have to boil mixture. Step three: mix $\ce{CO2}$ with hydrogen (hydrogen is produced by electrolysis of ...

14

I think some of the other transition elements have also catalytic properties. For example, rhodium is generally used in addition to platinum or palladium in catalytic converters to oxidize carbon monoxide and hydrocarbons on one hand, and reduce $\ce{NO_x}$ to nitrogen on the other hand. So, the choice is often made on the basis of relative cost. But of ...

14

According to original paper (1), KIT-6 is a highly ordered cubic $Ia3d$ silica ($\ce{SiO2}$) templated by Pluronic P123 ($\ce{[EO20PO70EO20]}$) block-copolymer surfactant. As a source of $\ce{Si}$, tetraethoxysilane (TEOS) or sodium silicate are primarily used. (1) Kleitz, F.; Choi, S. H.; Ryoo, R.; Chem. Commun. 2003, 0 (17), 2136–2137. DOI: 10.1039/...

13

Yes, the Raney nickel catalyst is different from simple, fine nickel powder. Raney nickel is prepared in two steps. First, the nickel is alloyed with aluminum and then in second step much of the aluminum is removed through a leaching process with sodium hydroxide. As the aluminum is removed two things happen. The resulting nickel-aluminum alloy becomes ...

13

Reaction conditions As Watts et al. have shown, the decomposition products of this Fenton-like reaction strongly depend on the $\mathrm{pH}$ of the solution.1 If performed in acidic conditions, the reaction generates mostly hydroxy radicals, but no reductants (which would be the hydroperoxide and superoxide anions). If, conversely, the reaction is held in ...

13

Some substances do exist that slow down reactions and they're different from catalytic inhibitors/poisons. Such substances are called negative catalysts. Here is one example I can think of right now: $$\ce{2H2O2 \xrightarrow{\large\mathrm{glycerol}} 2H2O + O2}$$ Glycerol, in this case behaves as a negative catalyst and slows down the reaction. Another ...

12

His work is about developping new catalysts based on copper and iron, to replace to traditional catalysts based on palladium. Copper and iron are both very common elements in nature, while palladium is considered a high supply risk (see the 2012 British Geological Survey risk list for details). The new RSC Visual Elements Periodic Table can be used to check ...

12

A naked aluminum surface (freshly sanded) in air immediately grows about 4 nm of adherent aluminum oxide that passivates the surface. Iodine slightly dissolves in water and disproportionates $$\ce{I2_{(s)} + H2O_{(l)} -> HOI_{(aq)} + I^{-}_{(aq)} + H+_{(aq)}}$$ Iodine is strongly solubilized by forming triiodide. $$\ce{I2 + I- -> [I3]-}$$ The ...

12

The used analytical reaction of purple permanganate to colourless $\ce{Mn^2+}$ occurs under acidic conditions: $$\ce{MnO4- + 8H+ + 5e- <=> Mn^2+ + 4H2O}$$ Under neutral conditions, permanganate would be reduced to dark brown manganese(IV) oxide: $$\ce{MnO4- + 4H+ + 3e- <=> MnO2 + 2H2O}$$ Therefore, sulfuric acid is added to make the solution ...

11

The role of the acid in this reaction (really a polymerization) is two-fold. First, it protonates the acetone carbonyl oxygen making the acetone carbonyl carbon more electrophilic. This speeds up the rate of attack by the nucleophilic hydrogen peroxide (or other hydroperoxides formed later in the reaction) on this carbon. Second, the acid also protonates ...

11

Here is a method for converting secondary and tertiary alcohols into the corresponding alkane using $\ce{InCl3}$ as a catalyst. Chlorodiphenylsilane is the only reagent used in addition to the catalyst. The method works in the presence of common functional groups leaving them untouched. Since primary alcohols are unreactive, this reaction can be used to ...

11

There are a couple of ways to think about this. First, considering your atom economy equation. Typically a catalyst is used in place of a stoichiometric reagent. A catalyst is (strictly speaking) not a reagent, so its effect on the atom economy is neutral. The alternative stoichiometric reagent is a reactant, so it will reduce the atom economy. This leads to ...

11

Yes, one expects both forwards and backward reactions to speed up as you suggest; there seems to be no reason why microscopic reversibility would be suspended. The point of the catalyst will be to speed up a reaction so that it can happen on a reasonable time-scale, say hours not days or even years, and also (industrially) to use less energy to do the same ...

11

Usually when we say something "burns", it's being oxidized. In the case of carbon dioxide only the oxygen can be oxidized, by displacing it as the element; that requires fluorine or a sufficiently powerful fluorinating agent. Carbon dioxide supports combustion, acting as the oxidizer instead of being oxidized, with some active metals such as magnesium. ...

11

KIT-6 is a mesoporous silica, the chemical formula is the same for all silica which is $\ce{(SiO2)_n}$. The tridimensional structure though is usually represented as

10

You make the assumption that the ozone concentration in the upper atmosphere is in equilibrium. It isn't. $\ce{O3}$ is a much less stable molecule than $\ce{O2}$ (the heat of formation from $\ce{3/2 O2}$ is $143~\mathrm{kJ/mol}$) and the concentration at equilibrium would be very low. A significant concentration exists in the upper atmosphere because $\ce{... 10 TL;DR Your Maxwell–Boltzmann diagram up there is not sufficient to describe the variation of rate with$E_\mathrm{a}$. Simply evaluating the shaded area alone does not reproduce the exponential part of the rate constant correctly, and therefore the shaded area should not be taken as a quantitative measure of the rate (only a qualitative one). There is a ... 9 Alkali metal, main group, and transition metal (TM) alkoxides all have significantly different chemistry. Early- and Late-TM alkoxides also have different behaviour, so we should split this family into at least four categories. All of them are basic and will decompose via hydrolysis if dissolved in water; however, this type of chemistry is not usually ... 9 That should pose no issue regarding the glass Without images to see how unevenly you will apply the heat, I have to modify my instinctual reaction "That cannot possibly be an issue" to "Most likely it will be OK". I'd be much more worried about variation in the distilling if you are at some point drawing a distillate. If you cannot control the heat flux, ... 9 The first answer is great and the borosilicate glass can indeed survive harsh conditions. Here I'd like to suggest a DIY-project to improve the efficiency of the heater and make the column be warmed more evenly. Take a sheet of fiberglass cloth, sew the heating element in a serpentine pattern with the fiberglass threads, then wrap the crafted heating mantle ... 8 When two materials precipitate at the same time, you'll often get an extremely intimate mix of the two. I'm assuming that the notation you've got here means a precipitate consisting of a mixture of both nickel (II) ions, iron (II) ions, and sulfide ions, or a mix of nickel and iron sulfides (NiS & FeS). Iron and nickel (II) have similar ionic radii and ... 8 For what it's worth, problems like this can be solved very nicely with Mathematica and I find that it provides access to some really cool chemistry even when the math is a bit overwhelming for some students. One can obtain the same solution as @ManishEarth with the following Mathematica code: soln = DSolve[ { wood'[t] == -wood[t] (k1 + k2 + k3), ... 8 This is the solution I get:$\$\begin{align}\rho _T(t) &= -\frac{K_2 \rho _{w0} \left(e^{\left(-K_1-K_2-K_3\right) t}-e^{t (-K4-K5)}\right)}{K_1+K_2+K_3-K4-K5}\\\rho _W(t) &= e^{\left(-K_1-K_2-K_3\right) t} \rho _{w0}\\\rho_C(t) &=\tiny{-\frac{\rho _{w0} e^{-t \left(K_1+K_2+K_3+K4+K5\right)} \left(K_2^2 K5 e^{\left(K_1+K_2+K_3\right) t} \left(e^{...

8

I'm only directly attacking your direct question, "what sort of catalysts might be used, and what are the performance / lifetime issues with them?" because the rest is ill-defined. I'll mention some electrochemical conversion aspects. I hope to illustrate why your question is problematic. There are several different products one could imagine reducing ...

8

This is a very limited situation, but benzylic alcohols can be reduced to the corresponding alkyl group with simple hydrogenolysis conditions, hydrogen gas with Pd/C. This is similar to the cleavage of benzyl ethers, a common protecting group. Looking at it this way, the reaction deprotects water. An example of this reaction that I ran long ago is depicted ...

Only top voted, non community-wiki answers of a minimum length are eligible