Reaction Mechanisms and Catalysis: Flashcards
Revise elementary steps, molecularity, pre-equilibria, catalysts versus intermediates, surface catalysis and enzymes.
Reaction Mechanisms and Catalysis: Flashcards
- QuestionWhat is an elementary step?Answer
A single molecular event (one collision or one molecule breaking apart) that happens exactly as written. Its rate law follows its coefficients.
- QuestionWhat is molecularity?Answer
The number of particles reacting in an elementary step: unimolecular (1), bimolecular (2), termolecular (3, rare).
- QuestionGive three tests of a proposed mechanism.Answer
The steps add up to the overall equation; the predicted rate law matches experiment; the steps are reasonable (mostly uni- or bimolecular).
- QuestionHow do you handle an intermediate in the slow step?Answer
Use the fast, reversible step before it (pre-equilibrium): K₁ = [intermediate]/[reactants], then substitute into the slow step's rate law.
- QuestionHow do you tell a catalyst from an intermediate in a mechanism?Answer
A catalyst is used first and regenerated later. An intermediate is made first and used up later.
- QuestionName the four stages of surface catalysis.Answer
Adsorption onto active sites, weakening of bonds, reaction on the surface, desorption of products.
- QuestionWhat is catalyst poisoning?Answer
A substance (such as lead or sulfur) binds permanently to the active sites, blocking them.
- QuestionWrite the Michaelis–Menten equation.Answer
v = Vmax[S] / (Km + [S]). Km is the substrate concentration at which v = ½Vmax.
- QuestionWhy does an enzyme's rate level off at high substrate concentration?Answer
All the active sites are occupied (saturated), so extra substrate cannot be processed any faster: v approaches Vmax.
- QuestionHow do competitive and non-competitive inhibitors differ?Answer
Competitive: binds the active site; more substrate overcomes it (Km appears larger, Vmax unchanged). Non-competitive: binds elsewhere; lowers Vmax.
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