AP Chemistry: Kinetics Student Notes

Intro to Reaction Rates

The Rate of a reaction is measured with the units

The chemical that is used to measure the rate is determined by:

For Example

The reaction:

2NO2(g) ® 2NO(g) + O2(g)

Graph: What happens to the concentrations of both reactants and products as the reaction progresses. What is the rate of the reaction displayed graphically?

Rate Laws—Types

Two Types

  • ______
  • ______

______Rate Law

Rate = k[A]x[B]y

k = rate constant: found only by experiment

Determining the ORDER of the rate law

Rate = k[A] ______Order

Rate = k[A]2 ______Order

Rate = k[A][B] ______Order

Rate = k[A][B]2 ______Order

Units of k:

The units of k depend on the order of the rate law

Examples:

______Rate Law

y=mx+b

y has the term for the rate and x has the term for time.

Zero Order

1st Order

2nd Order

Method of Initial Rates

Rules

1.  Choose two experiments such that all but one variable cancels when divided.

2. 

3.  Cancel all but one of the exponents and then repeat to find x and y

4.  Use one (or the average of all) of the experiments to determine the value of k.

5.  Use dimensional analysis to determine the units of k

Example 1:


Integrated Rate Law

This law is used when a plot of ______vs ______is used.

First Order

Plot ______vs ______to get a straight line

Second Order

Plot ______vs ______to get a straight line

Zero Order

Plot ______vs ______to get a straight line

Graphs

How to determine the Order:

Rules

1.  Make a table as below

2.  Plot graphs of each and determine which line is the straightest. (This is easily done on a graphing calculator, but not necessary

a.  STAT EDIT (Enter time into L1 and concentration into L2)

b.  Go to L3 and type ln(L2)

c.  Go to L4 and type 1/(L2)

d.  Quit

e.  STAT CALC LinReg L1,L2 (Check correlation, r2) The closer to 1 or negative 1 the straighter the line

f.  Repeat with other lists: L1,L3 and L1, L4: Straightest line wins.

3.  The slope of the line will be the value of k. k is always positive so if you get a negative slope then the value is just the absolute value of the slope.

Summary Table of Rate Law Equations found on page 572

a.  Reaction Mechanisms

Reactions happen through a series of ______

There are three kinds of steps

Unimolecular

Bimolecular

Termolecular

Some steps are fast and some steps are slow. The rate of the reaction is determined by the ______and this is called the ______.

Chemicals that appear on the product side and then eventually disappear are called ______or simply ______.

For a reaction, the mechanism must meet two criteria for it to be a plausible mechanism:

1.  ______

2.  ______

Catalysis

Definition:

a.  A substance that speeds up a reaction without ______

b.  A chemical that lowers the ______

c.  BY—Changing the ______

- 1 -