1) why arent they consumed in the reaction ( can you explain step by step how it influences the reaction?)
2) is it energy related?
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It is indeed energy related. In order to get a chemical reaction happening you need a certain amount of initial energy. But a catalyst is able to react to the initial chemicals using less initial energy and then again further to complete the reaction. But even though the catalyst is part of many of the intermediate reactions the end result have the catalyst in the same state as it started in. This is by definition. If this was not the case then we would not call it a catalyst.
Saying that a catalyst is not consumed is a bit misleading. This is because in practical applications it is very hard to keep the catalyst in place during the reaction. It is part of the reaction which means it forms into new chemical compounds and takes on new state of matter. So it might not be in the same place at the end of the reaction as it was at the start of the reaction. This means that practically speaking you are consuming some catalyst.
If you imagine a chemical reaction is someone trying to cross a river, the catalyst works like a ferry.
Sure, you could swim all the way, but that would cost a lot of energy. Instead, you can just ride the ferry to the other side, and you will get to transform into product, while the ferry can keep working.
In more chemical terms, how catalysts works depend on each reaction, but usually the catalyst is going to make a temporary bond with one of the reagents, and form an intermediary product, which is then converted into the final product regenerating (usually) the catalyst. This reduces the Activation Energy, the energy necessary to start a reaction, much like you need a spark to start a fire.
Compound with elements A and B reacts with element C to create compound AC and loose element B. Compound AC then breaks down naturally due to instability. You now have elements A, B, and C completely separate from each other. You should note that element C started the reaction, and finished the reaction in the same state, and as such, is a catalyst.
Different catalyzing reactions work differently, but they all end up where they started. If the element got consumed in the reaction, then it would be a *reactant* not a catalyst.
Now, because it is reacting to the other compounds, and chemical reactions aren’t perfect, most catalysts will degrade over time, but most of the time, it ends up separate from the reactants.
Yeah, it’s energy related. All reactions have a minimum starting energy they need to get going, catalysts provide a separate path that has a lower minimum energy than the direct reaction.
Well, consider a concrete example: destruction of ozone by chlorine. The reactions are:
* Cl + O3 => ClO + O2
* ClO + O3 => Cl + O2 + O2
That is, chlorine (Cl) reacts with ozone (O3) to produce chlorine monoxide (ClO) and oxygen (O2). The chlorine *is* consumed in the reaction. But then a second reaction occurs: the chlorine monoxide reacts with more ozone to produce chlorine and more oxygen. So then we have chlorine again, which is the same chemical we started with. So when we consider the sequence as a whole (which amounts to Cl + 2O3 => Cl + 3O2), the chlorine was not consumed.
And, I mean, yes, you can talk about it in terms of energy. O3 is lower energy than O2 + O, so the ozone molecules are somewhat stable on their own. But Cl + O3 is higher energy than ClO + O2, so chlorine can break ozone molecules. And then ClO + O3 is also higher energy than Cl + 2O2, so chlorine monoxide can *also* break ozone molecules.
TLDR; Lowers activation energy meaning it kicks off chemical reactions like you light up paper so the flames start spreading. Example for mechanism, scroll down to ethanol synthesis
So chemical reactions work with energy. If a chemical reaction happens, it either relesses energy (meaning the outcome is more stable) or takes it (you basically force a reaction that doesn’t want to happen). This basically is how your smartphone battery works. If you charge it, you give it electrical energy. The chemicals take this energy to react and form less stable things (that have higher energy). Using your smartphone releases the energy
This happens by a reaction that forms more stable chemicals, the energy is given off.
But every reaction still need energy to kick off the reaction. Imagine a hill with a ball on it. The higher sits, thr higher it’s energy. If the ball can, he will just roll down and decrease it’s energy. But our hill has a small incline! So in order to roll down you actually need to give it a little kick or else ir just sits there uphill. We call this kick the “activation energy (lets abbrecviate it to AE) “, the energy required to start the reaction.
It is also known that the speed of a chemical reaction is directly dependent on the activation energy.
For many reactions, the AE is very low, so it happens instantly. For many others, it is very high. This is the reason why we don’t just ignite in air. Even though we could. The energy to start the burning reaction is waaayy to high.
Catalysts choose a different reaction pathway that loerrs the activation energy. So chemical reactions happen thaz otherwise woukd not have kicked off. Because the molecules seek the lowest energy, the start following whatever the catalyst is doing. It’s as if the catalysts bores a hole through the little incline. But as a trade off, thr ball has to get green, because the boring machine is full of green paint.
So not only do we have thr ball at the ground level now. Something that requires a big kick off (like heat).But it is also green, something that could have never happend without the boring machine, even with heat.
For your other question, here is the synthesis of ethanol as an example (not really used, but you can do it).
H2C=CH2 + H2O -> H3C-CH2OH
This reaction doesn’t happen. Unless we catalyze that with sulfuric acid.
H2SO4 -> HSO4- + H+ (our catalyst was just used)
H2C=CH2 + H+ -> H3C-CH2+
H3C-CH2+ + H2O -> H3C-CH2OH + H+
HSO4- + H+ -> H2SO4 (our catalyst is back)
This is of course a bit simplified, but you see that we get back the catalyst in the reaction and it’s ready to do this exact same process roughly 10^23 times.
For a lot of things, the catalyst is a surface of some type. One of the reactants attaches itself to the catalyst, and that binding process causes the reactant to slightly change its shape (which consequently makes the reaction barrier lower). Then the second reactant can come in and has better access to react with the first one—maybe the binding process leaves the reaction site a little more exposed, maybe it just moves some of the electrons around enough to make it a more reactive site. Once the reaction has happened, the products are able to release from the catalyst and move on.
You can think about it sort if like trying to write on a piece of paper. You can hold the paper in one hand and draw on it with the other, but it’s faster and easier if you put the paper down in a table first. When you’re done, the paper and your writing implement are both changed (slightly) but the table is just the same as it was.
Catalysts effectively make an environment the promotes a reaction. They mostly do this two ways: they make a physical pocket that two molecules fit into so they line up just right, and they have atoms that have hydrogen or electrons positioned to push/pull electrons on molecules in a way that favors a reaction. Some also temporarily lend an electron or hydrogen to a reaction.
The catalyst is not consumed because it’s not changed when the reaction it catalyzes takes place. All it does is make the reaction more favorable and quicker / require less energy to happen.
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