by lowering the activation or "Trigger" energy.

To expand on YT's answer, catalysts bring the reactants together in the right positions to react. For example, enzymes, which are biological catalysts, do this by having "active sites" specific for the substrate (what they act upon). When the substrate or substrates bind, the active site changes to reduce the activation energy. It might bring two molecules together to join them, or it might strain a bond to split a molecule. Once the reaction is complete, the enzyme releases the product(s) and can be reused.

A very complicated, biological reaction requiring light: photosynthesis. YT, Agitation would not fit under surface area, since under any specific area the reaction can be agitated. Whether its a test tube of 20 mL or a test tube of 100mL, agitation provides 'excessive' collisions between molecules. Atoms/molecules can only interact with each other if they are being 'hit' by another atom/molecule. Increasing the collision frequency is directly proportionate to bonds created.

sorry but I must disagree with you there (and I hate disagreeing with good people)

collisions are brought about by thermal causes as the molecules vibrate at a much higher rate, agitation I reccomend be under the surface area catagory as there would be insufficient energies to qualify as proper "collisions" but enough energy to keep most surface areas exposed

Light isn't a catalyst, it's a reactant in it's own right! Just because it's little doesn't mean it's not important!

YT2095 said in post # :

sorry but I must disagree with you there (and I hate disagreeing with good people)

collisions are brought about by thermal causes as the molecules vibrate at a much higher rate, agitation I reccomend be under the surface area catagory as there would be insufficient energies to qualify as proper "collisions" but enough energy to keep most surface areas exposed

If you're talking about Brownian Motion, that's a manifestation of agitation and not surface area.

 

Surface area is an attribute of the reactants, not the reaction. The reactants can have as much surface area as they like but this won't necessarily change the rate of collisions.

 

[surface area absolute] and [% chance of collision] are not the same thing.

this maybe usefull to read also: http://scidiv.bcc.ctc.edu/wv/7/0007-005-rea-t-cat.html

Ok. Thanx alot guys. Thanx for the info!