halophilic substitution,heterogenous and homogenous catalysis?

[youngjock]

I was just doing an MCAT question, it had those 3 choices. I don't know what they are, can you explain?

thanks.

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[Spudster]

A few hints for you...
HALOphilic - halo, think halogens
HETERO vs. HOMO catalysis - different vs. same phase catalyst

 

[youngjock]

what is a heterogenous catalysis?

a combination of mixed catalysts?

•••quote:•••Originally posted by Spudster:
•A few hints for you...
HALOphilic - halo, think halogens
HETERO vs. HOMO catalysis - different vs. same phase catalyst•••••

 

[mr.annoying]

nerds

 

[CoffeeCat]

You can try the MCAT forum :wink:

 

[guitarguy]

In heterogeneous catalysis, the catalyst/enzyme and substrate are of the same phase (solid, liquid, gas). In homogeneous catalysis, however, they are of the same phase. Organic chemists know from experience the optimum conditions under which a certain reaction can be catalyzed. Hetero. and homo. catalysis have various advantages and disadvantages for every reaction. For the MCAT, besides these definitions, you should probably just be familiar with the fact that a major disadvantage of homogeneous catalysis lies with the fact that the substrate and enzyme cannot always be easily separated after catalysis has occurred. My guess is that halophilic substitution refers to a substitution reaction (SN1 or SN2) involving halogens. Usually you can eliminate these ambiguous answer choices on the MCAT.

 

[guitarguy]

Oops, I meant to say that in heterogeneous catalysis, the catalyst/enzyme and substrate are of different phases

 

[Spudster]

Perhaps an example to clarify...

One every day example of HETEROgeneous catalysis is the simple catalytic converter in your car - there is solid Pt embedded in a solid support over which the exhaust gases flow. The Pt is a catalyst for a reaction that removes some of the more onerous compounds produced by the internal combustion engine.

So, HETERO since solid catalyst and gaseous substrate.

 

[youngjock]

thanks for the answers.

<a href="http://www.geocities.com/youngjock4u/mcat.jpg" target="_blank">http://www.geocities.com/youngjock4u/mcat.jpg</a>

that is the whole problem. i just scanned it.

the question is
"what type of reaction is illustrated by step 3?"

can someone tell me why "heatero catalysis" is the correct one? thanks.

 

[Doctor Octopus]

You have a solid phase catalyst (Palladium/Carbon) and your substrate is in the aqueous phase. Two different phases = hetero

 

[The Fly]

Definitely getting orgo flashbacks. . .

PLEASE take this somewhere else!! :wink:

 

[Bikini Princess]

•••quote:•••Originally posted by Doctor Octopus:
•You have a solid phase catalyst (Palladium/Carbon) and your substrate is in the aqueous phase. Two different phases = hetero•••••Far more often, however, is when your substrate is in the organic phase, and your catalyst is in the aqueous. This gives a constant recycling of catalyst at the phase boundary.

Oh how I wish i was in P-chem again making phase diagrams! ~Sigh~

 

[medname]

Hey-

Just a tip for studying for the MCAT-

There is so much material that you may be losing time spending 20+ minutes trying to figure this kind of thing out. Look in you text and then quickly more on.