[TabooTalk]

My instructor asked the following question:

What is the catalyst in the reaction C2H4+H2+Pt?

I've viewed his PowerPoint presentation and he says that a catalyst is something added to a reaction in order to speed it up or slow it down. That's great, but he doesn't ever explain to us how to determine what component of a reaction is the catalyst. Is there an easy way to look at a problem and instantly know what the catalyst is? He also gives us reactions without a catalyst and tells us to specify what agent could be added as a catalyst.

I tried looking this up online and found this question (which is very similar to the ones on my instructor's homework assignment:

What is the catalyst for the reaction between isoprene and hydrogen?

Someone answered: "Nickel"

How did they come to this conclusion? I've read the entire chapter that has information on catalysis, but it doesn't speak in laymen terms so I'm not better off than when I started.

Can you guys give me some pointers please?

[Arkcon]

A catalyst has another property used to identify it.  Do you have a better definition of catalyst in your text book?  You may be able to tell, which is the catalyst, if you have a complete reaction:  starting reactants and resulting products.

[TabooTalk]

Could that first one be a trick question? He does that a lot.

Here's another example question:

The catalyst in the reaction C2H4 + H2 + Pt → C2H6 + Pt is
a. C2H4
b. H2
c. Pt
d. C2H6

I'm guessing the catalyst would be Pt, because it is the only one that is separate on both sides of the reaction. I doubt most questions would be this easy though. He said on the exam we will have to name a good catalyst to add to a reaction, and that is where I'm really worried. (like the example in my OP regarding hydrogen, isoprene, and nickel) I do not know how to determine which element will speed up (or slow down) a reaction. What properties do I have to look for in an element? Does this make sense?

I'm generally quite good at chemistry, at least I've earned a B thus far this year, but I can't seem to be able to grasp this concept of the course. It is driving me a bit mad.

[Dan]

I'm guessing the catalyst would be Pt, because it is the only one that is separate on both sides of the reaction.

Basically yes, but do what Arkcon suggested: Find a complete definition of the term catalyst and see if it starts to make more sense.