Insight 2010 Multi Choice

[toshibaj]

Hey guys, this one question from the insight exam is bugging me.

Question 2

Which changes will result in a greater proportion of successful collisions between reactant particles.

I     addition of catalyst
II    grinding reactant lumps into a powder
III   increasing concentration of reactants

The answer states that I increases the proportion of successful collisions and that II and III only increase the total number of successful collisions.
 
Is this correct?

[scocliffe09]

Hey guys, this one question from the insight exam is bugging me.

Question 2

Which changes will result in a greater proportion of successful collisions between reactant particles.

I     addition of catalyst
II    grinding reactant lumps into a powder
III   increasing concentration of reactants

The answer states that I increases the proportion of successful collisions and that II and III only increase the total number of successful collisions.
 
Is this correct?

addition of a catalyst definitely increases the proportion of successful collisions.
Grinding lumps into a powder leaves more surface area exposed i.e. more molecules exposed for more collisions and thus faster reaction. I don't think that powdered molecules have any higher chance / proportion of successful collisions though, as their energy pathway is the same as when they are in a lump.
increasing concentrations, again, causes more collisions, but their reaction pathway is the same, activation energy is the same as it was before and thus proportion of successful collisions is unchanged. (think of an energy profile - none of these changes alter the energy of products or reactants (i.e. don't change delta H) but catalysts reduce activation energy)
hope that helps.

[Xavier1234]

Hey guys, this one question from the insight exam is bugging me.

Question 2

Which changes will result in a greater proportion of successful collisions between reactant particles.

I     addition of catalyst
II    grinding reactant lumps into a powder
III  increasing concentration of reactants

The answer states that I increases the proportion of successful collisions and that II and III only increase the total number of successful collisions.
 
Is this correct?

yeah. try drawing a graph of it. if you use a catalyst, the bonds of the reactants are weaker, hence the activation energy is smaller and rate increases bla bla. knowing that, a greater proportion of collisions will be deemed successful since 'the cut off' energy is lowered.

[toshibaj]

ah k thanks guys. I guess I was thinking too literally.