CHEM 113 1st Edition Lecture 6 Current Lecture16.6: Reaction Mechanisms: The steps from reactant to product- Reaction Mechanismso The mechanism of a reaction is the sequence of single reaction steps that make up the overall equation.o The individual steps of the reaction mechanism are called elementary steps because each one describes a single molecular event. Each elementary step is characterized by its molecularity, the number of particles involved in the reaction. - Types of molecularity of elementary stepso Unimolecular reaction: reaction that involves the decomposition or rearrangement of a single particle.o Bimolecular reaction: one in which two particles reacto Can be the two of the same particles or two different particles.o Termolecular: Three particles are used, these are extremely rare because the probability of three particles colliding simultaneously with enough energy and an effective orientation is very small. Because an elementary reaction occurs in one step, its rate law, unlike that for an overall reaction, can be deduced from the reaction stoichiometry. - Reaction order equal molarity!- Therefore, we use the equation coefficients as the reaction orders in the rate law.o Unimolecular: Rate = [A]o Bimolecular (same particle): Rate= k[A]^2o Bimolecular (two different particles): Rate= k[A][B]- Correlating mechanism with the rate lawo A valid mechanism must meet three criteria: The elementary steps must add up to the overall balanced equation.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. The elementary steps must be reasonable. The mechanism must correlate with the observed rate law.o A mechanism is a hypothesis, we cannot prove it is correct but if it is consistent with the data and can be used to predict results accurately, it is a useful model for the reaction.- The rate-determining step of a reactiono The slowest step in a reaction is the rate-determining or rate-limiting step.o The rate law for the rate-determining step becomes the rate law for the overall
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