Lecture 6: Catalysts Flashcards
catalysts homogeneous catalyst heterogeneous catalyst enzyme rate expression competing/parallel reactions explosions oscillating reactions
Define a catalyst
substances which speed up the rate of the reaction; without being CONSUMED in the overall process; usually react in the early step in the reaction mechanism
regenrated again in a later step
What does homegeneous catalyst mean?
a catalyst which is the same phase as the reaction itself ( like aliquid phase acid catalyst)
What does heteroegneous mean?
a catalyst which is a DIFFERENT phase as the reaction itself (eg. metal catalyst Pt during hydrogentation of an alkene)
Does the concentration of a catalyst usually appear in the rate expression?
yes. [H3O]+ is involved in the slow transfer of a proton eg. to a carbonyl group
rate = k[ester] [H3O]+
What does a catalyst provide which enables it to lower the Ea barrier of a reaction?
it provides an alternative reaction pathway of lower activation energy; therefore the rate of the reaction will be faster
What is an enzyme?
a biological catalyst, usually a large protein, the reaction occurs at its active site
What happens during competing/ (parallel) reactions
lead to different products from the same reactants
Why does an explosion occur?
because the concentration of reactive intermediates increase rapidly as the reaction proceeds
What happens during an oscillating reaction
the product appears as a series of bursts, and he concentrations of intermediates rise and fall periodically with time
What happens during the Michaelis and Menten mechanism
a substrate and enzyme react REVERSIBLY to form short lived ENZYME SUBSTRATE COMPLEX
in the slow step, this complex then BREAKS DOWN to form the product, plus the enzyme again
