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chem 2--exam2
ch#13.4-13.9, ch#14, ch#15
Question | Answer |
---|---|
chemical kinetics | is the study of how fast chemical reactions occur |
reaction rate | aA + bB ---->cC + dDreactants are (-) and products are (+) |
what does the reaction depend on | it depends on the amount of reactants that are present |
method of initial rate | you measure the rate at the beginning of the reaction; after mixing the reactants, and assume that the reactant concentrations does not change enough to change the reaction rate |
instateneous rate | is the rate of a reaction changes as it poceeds it decreases. as the reactants are used up. this tells us that the rate of the reaction in general depends on the cencentration of the reactants and this gives us the rate law. |
units for rate | mol/liter sec or mol/liter min |
rate constant | takes whatever units it must in order for the rate units to be correct, and this depends on the order of the reaction |
integrated rate laws | expresses the time dependence of reactant concentrations. need reactant concentration as a function of time |
first order reaction | rate = k[A] |
half life | is the amount of time it takes from the [A] = 1/2 [A]o |
example | isomerization of cis-2-Butene |
explain the series of reaction called mechanism | it must be simple. an overall reaction can be an elementary reaction, but more commonly, an overall reaction consists of series of elementary reactions that had form reactants to products. this series of reaction is called the mechanism |
how do you determine validity of a mechanism | knowing the rate law |
3 types of elementary reaction | unimolecular, bimolecular, trimolecular |
unimolecular | only 1 molecule by itself react. simple, ex isomerization of cis-2-butene,and it reacts with 1st order rate laws. rate = k[A] |
bimolecular | 2 molecules (or atoms or ions) react with each other, reactions must have 2nd order rate laws. rate = k [I] [CH3Br] |
trimolecular | 3 molecules (atoms or ions) react with each other. ex have 3rd order rate law, but these are very rare (3 things collide) |
intermediate | is an species produced in one step of a mechanism and consumed on a later step |
catalyst | is a substance that increases the rate of reaction without being consumed |
what is an elementary reaction | is a sone step precess whose equaation describes which nanoscale particles break apart, rearrange their positions, or collide to make a reaction occur. |
equilibrium is | the rate of the forward reaction is equal to the rate of the backward reaction |
forward rate is | cis (f) |
backward rate is | k(b) trans |
k (c) | equilibrium constant and is a function of temperature only |
k (c) is equal to | products/reactants |
k (b) is < 1 then is favored to | the reactants because the products are smaller than the reactants. |
k (b) is > 1 then is favored to | the products. this is a typical for reactions that go, to compleation and not equilibrium. |