Chapter 15: Chemical Kinetics Flashcards Preview

Chemistry 143 > Chapter 15: Chemical Kinetics > Flashcards

Flashcards in Chapter 15: Chemical Kinetics Deck (29)
Loading flashcards...
1

Rate of reaction is impacted by what factors?

- Collision model (concentration of reactant particles) - Temperature of reactant mixture (generally occur faster with increasing temperature) - Structure and relative orientation of colliding particles

2

Rate of Reaction (definition)

- Measure of how fast the reaction occurs - Large fraction of molecules is produced from a faster rate

3

Speed Equation

change in distance / change in time = ∆x / ∆t

4

Instantaneous Rate of Reaction: aA + bB --> cC + dD

Rate = -1/a (∆[A]/∆t) = -1/b (∆[B]/∆t) = +1/c (∆[C]/∆t) = +1/d (∆[D]/∆t)

5

Rate Law

Express relationship between rate of reaction and concentration of reactant:
Rate = k[A]n

k = constant of proportionality (rate constant)
n = reaction order

6

Reaction Order:

n = 0

- Zero order

- Rate is independent of concentration

- Concetration decreases linearly over time

- Occurs when amount of reactant available for reaction unaffected by changes in overall quantity of reactant

7

Reaction Order:

n = 1

- First order

- Directly proportional to concentration

- Rate slows down as reaction proceeds

8

Reaction Order:

n = 2

- Rate of reaction proportional to square concentration of reactant

- Rate is more sensitive to concentration

9

How to determine order of reaction?

- Order of reaction is determined by experiment

- Common method is to use method of initial rates

k = rate 2 / rate 1 = k[A]n2 / k[A]n1

10

Integrated Rate Law

- Relationship between concentrations of reactants and time

11

First Order Integrated Rate Law

ln[A]t = -kt + ln[A]0

slope = -k

12

Second Order Integrated Rate Law

-∆[A] / ∆t = k[A]2 or

1/[A]t = kt + 1/[A]0

NONLINEAR

13

Half-Life 

t1/2 = 0.693/k

14

Arrhenius Equation

k = Ae-Ea/RT

- Ea = activation energy

- Frequency factor (A): number of times the reactants approach activation barrier/time

- Frequency factor (Ea): Energy barrier to be surmounted by reactants

- In a graph, E of products will be contained on the right side after bump in activation energy

15

Activated Complex

- Transition state in which it has a higher energy than either reactant or product

16

Exponential Factor

- Number between 0 and 1 representing fraction of molecules that have enough E to make it over the activation barrier on given approach

= e-Ea/RT

17

Arrhenius Plot

- Plot of natural log of rate constant (lnk) versus the inverse of temperature in Kelvins (1/T) 

- Creates straight line with slope -Ea/R and y-intercept lnA

18

Two-Point Arrhenius

lnk2/k1 = Ea/R (1/T1 -1/T2)

19

Collision Model

- Chemical reaction occurs after a sufficiently energetic collision between two molecules

20

Orientation Factor

- Measure of how specific the orientation of the collision must be

21

Reaction Mechanism

- Series of individual chemical steps by which an overall chemical reaction occurs

- Comprised of elementary steps (each step in the reaction mechanism)

22

Molecularity

- Number of reactatnt particles involved in step; used to characterize elementary steps

- Unimolecular, bimolecular, termolecular

23

Rate Determining Step

- Limits the overall reaction and determines the rate law for the overall reaction

- Obtain rate law from "slow step"

24

Catalyst

- Substance that increases rate of chemical reaction but is not consumed by the reaction

- Provides alternative mechanism for reaction (in which rate-determining step has lower Ea)

25

Homogenous Catalyst

- Catalyst exists in same state as reactants

 

26

Heterogenous Catalyst

- Catalyst exists in different phase than reactants

 

27

Hydrogenation

- Involves hydrogenation of double bonds of alkenes

28

Catalyst Procedure

1) Absorption: Reactants absorbed onto metal surface

2) Diffusion: Reactants diffuse on surface until they approach each other

3) Reaction: Reactants react to form products

4) Desorption: Products desorb from surface to react

29

Enzymes

- Biological catalysts that increase rates of biochemical reaction

- Usually large protein molecule with 3D structures

- Active site: Binds reactant molecule

- Substrate: Fits into active site (only catalyze one substrate)