Chemical kinetics

varun i dont think that definition is there everywhere. I can show you sources where the definiton of catalyst is something else altogether.. but lets not get into that :)

I am sure that if NCERT says that.. we should not conflict it. I dont think IIT Profs take (neither should they) any other book as a standard(if at all they do) .... I know my extreme limitations in Chemistry.. but still i pulled myself into this discussion)

A word of caution!

Be very careful if you are asked about this in an exam. The correct form of words is

"A catalyst provides an alternative route for the reaction with a lower activation energy."

It does not "lower the activation energy of the reaction". There is a subtle difference between the two statements that is easily illustrated with a simple analogy.

Suppose you have a mountain between two valleys so that the only way for people to get from one valley to the other is over the mountain. Only the most active people will manage to get from one valley to the other.

Now suppose a tunnel is cut through the mountain. Many more people will now manage to get from one valley to the other by this easier route. You could say that the tunnel route has a lower activation energy than going over the mountain.

But you haven't lowered the mountain! The tunnel has provided an alternative route but hasn't lowered the original one. The original mountain is still there, and some people will still choose to climb it.

In the chemistry case, if particles collide with enough energy they can still react in exactly the same way as if the catalyst wasn't there. It is simply that the majority of particles will react via the easier catalysed route.

source: http://www.chemguide.co.uk/physical/basicrates/catalyst.html

btw you must have heard.. that inhibitors are used in a nuclear reaction to reduce the speed or the rate of nuclear reaction.

Otherwise there is an exponential increase (as you must have read/known)

Just recalled this from my course on nuclear from IIT :)

http://www.chem4kids.com/files/react_catalyst.html

this is one source (not an authentic one i must confess.. but just for refernece for what is the difference between catalyst and inhibhitor!!)

it is called "Inhibitors" just google for this term :) ;)

i hope this settles all issues :)

Read section 4.5.1 page 114 of NCERT. I have read 3-4 very very authentic sources (in my view!) for this and they all say that a catalyst decreases the activation energy

@sky (Yes even i read that and that was my first reaction on seeing this question. That only correct answer should be "c" !) but a lot of what we read then has gone into the dustbin ;) :(

Is it (c)?

dont go by the wiki.. but Varun i think if NCERT says that then yes b has to be an option

@sky.. to me and i think for all guys giving AIEEE, JEE should not try to conflict anything given in NCERT (why i am saying this is that the book is prepared by the best ppl in India. There is a big group that does it and every single line in there has been discussed by these people before putting it in there!) To that extent it is the bible.

Does any of you have the NCERT chemistry book. I wud say that the best place to verify this definiton is that book

No other book!

but i think that may be varun u are right.

The definiton of catalyst as i remember it is that some substance that increases or decreases the rate or reaction........

no it is not necessary that a catalyst always causes an increse in the reaction speed!