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chem_ch12
| Question | Answer |
|---|---|
| the area of chemistry that concerns reaction rates | chemical kinetics |
| is the change in concentration of a reactant or product per unit of time | reaction rate |
| rx rate= | conc. of A at t2-conc. of A at t1/t2-t1 |
| reaction rate is always _____, but we define it as a _______ # | negative; positive |
| rate= | K[molecule]^n |
| the arrangement of atoms found at the top of the potential energy barrier as reaction proceeds from reactants to products | activated complex (transition state) |
| the threshold energy that must be overcome to produce a chemical reaction | activation energy |
| the equation representing the rate constant as k=Ae^Ea/RT, where A represents the product of the collision frequency and the steric facot and e^-Ea/RT is the fraction of collisions with sufficient energy to produce a reaction | Arrhenius equation |
| a reaction involving the collision of two molecules | bimolecular step |
| a substance that speeds up a reaction without being consumed | catalyst |
| the area of chemistry that concerns reaction rates | chemical kinetics |
| a model based on the idea that molecules must collide to react; used to account for the observed characteristics of reaction rates | collision model |
| an expression that gives the rate of a reaction as a function of concentrations; often called the rate law | differential rate law |
| a reaction whose rate law can be written from its molecularity | elementary step |
| a large molecule, usually a protein, that catalyzes biological reactions | enzyme |
| the time required for a reactant to reach half of its original concentration | half-life of a reactant |
| an expression that shows the concentration of a reactant as a function of time | integrate rate law |
| a species that is neither a reactant nor a product but that is formed and consumed in the reaction sequence | intermediate |
| orientations of molecules during collisions, some of which can lead to reactions while others cannot | molecular orientations |
| the number of species that must collide to produce the reaction represented by an elementary step in a reaction mechanism | molecularity |
| the positive or negative exponent, determined by experiment, of the reactant concentration in a rate law | order |
| the proportionality constant in the relationship between reaction rate and reactant compositions | rate constant |
| an expression that shows how the rate of reaction depends on the concentration of reactants | rate law |
| the slowest step in a reaction mechanism, the one determining the overall rate | rate-determining step |
| the series of elementary steps involved in a chemical reaction | reaction mechanism |
| the change in concentration of a reactant or product per unit of time | reaction rate |
| a reaction involving the simultaneous collision of three molecules | termolecular step |
| a reaction step involving only one molecule | unimolecular step |
| chemica reactions are _____ and the reverse reaction can also occur | reversible |
| depends on how the rate is defined | rate constant |
| often simply called the rate law | differential rate law |
| expresses how the rate depends on concentration | differential rate law |
| two types of rate laws | differential rate law and integrated rate law |
| expresses how the concnetration depends on time | integrated rate law |
| a common experimental method for determining the rate law | method of initial rates |
| several experiments are carried out with different initial concentration of reactants | method of initial rates |
| only the forward reaction is important | method of initial rates |
| is the sum of n and m | overall reaction order |
| for an nth order reaction the units of k will be | L^n-1/mol^n-1s |
| the time required for a reactant to reach half of its original concentration | half life |
| n=0 integrated rate law | [A]=-kt + [A]0 |
| n=0 half life | t1/2 = [A]0/2k |
| n=1 integrated rate law | ln[A]= -kt + ln[A]0 |
| n=1 half-life | t1/2 = 0.693/k |
| n=2 integrated rate law | 1/[A] = kt + 1/[A]0 |
| n=2 half-life | t1/2 = 1/k[A]0 |
| describes how a chemical reaction occurs | reaction mechanism |
| can never be proved absolutely | reaction mechanism |
| consists of a series of elementary steps | reaction mechanism |
| is a reaction whose rate law can be written from its molecularity | elementary step |
| is the number of species that collide to produce the reaction indicated by an elementary step | molecularity |
| when the step only involves one molecule | unimolecular |
| when the step involves two molecules colliding with each other | bimolecular |
| when the step involves theree molecules colliding with each other simultaneously. This rarely happens | termolecular |
| two criteria must be mut if a mechanism is to be considered acceptable | 1. the sum of the elementary steps must give the overall balanced equation for the reaction. 2. the mechanism must agree with the experimentally determined rate law |
| a species that is neither a reactant or a product | intermediate |
| is formed and consumed during the reaction sequence | intermediate |
| the slowest step | rate-determining step |
| the overall reaction can be no faster than this step | rate-determining step |
| there are two important empirical (experimental) facts about the rate of chemical reactions | 1. the more concentrated the reactants, the faster the reaction. 2. the higher the temperature, the faster the reaction |
| says that molecules must collide to react | collision model |
| used to accound for the observed characterisitcs of reaction rates | collision model |
| two requirements must be satisfied for reactants to collide successfully | 1. the collisions must involve enough energy to produce the reaction; that is the collision energy must equal or exceed the activation energy 2. the relative orientation of the reactants must allow formation of any new bonds necessary to produce products |
| the threshold energy that must be overcome to product a chemical reaction | activation energy |
| rate depends on the size of | Ea |
| the bigger Ea is | the slower the rate |
| the arrangement of atoms found at the top of the potential energy barrier as reaction proceeds from reactants to products | activated complex (transition state) |
| this complex cannot be isolated and studied | activated complex |
| you can't store it in a container. It's too unstable. | activated complex |
| many collisions, even though they have the required energy, still do not produce a reaction. why? | their molecular orientations during collisions are not correct |
| arrhenius equation | k = Ae^-Ea/RT |
| is the frequency factor | A |
| Ea can be calculated from the values of k at only two temperatures by using this equation: | ln(k2/k1) = Ea/R (1/T1 - 1/T2) |
| is a substance that speeds up a reaction without being consumed itself | catalyst |
| provides a new pathway for the reaction, one with a lower Ea | catalyst |
| does not affect the energy difference delta E between products and reactants | catalyst |
| a large molecule, usually a protein, that catalyzes biological reactions | enzyme |
| many of the complicated biological reaction which keeps us aluve would not occur wihtout them | enzyme |
| two classes of catalysts | homogeneous catalyst and heterogeneous catalyst |
| are present in the same phase as the reactants | homogeneous catalyst |
| exists in a different phase (usually solid) | heterogeneous catalyst |
Created by:
md4