Properties of Solutions
Colloids, or colloidal dispersions, are suspensions in which the suspended
particles are larger than molecules but too small to separate out of the
suspension due to gravity.
Particle size ranges from 5 to 1000 nm
14.1 Factors that Affect Reaction Rates
Chemical kinetics is the study of how fast chemical reactions occur.
There are several important factors which affect rates of reactions:
physical state of the reactants,
concentration of the
14.3 Concentration and Rate
In general, rates:
increase when reactant concentration is increased.
decrease as the concentration of reactants is reduced.
We often examine the effect of concentration on reaction rate by
14.4 The Change of Concentration with Time
Goal: Convert the rate law into a convenient equation that gives
concentration as a function of time.
For a first-order reaction, the rate doubles as the concentration
Temperature and Rate
Most reactions speed up as temperature increases.
We can illustrate this with chemiluminescent Cyalume light sticks.
A chemiluminescent reaction produces light.
Two light sticks are placed in water, one at room
Arrhenius: Molecules must posses a minimum amount of energy to
In order to form products, bonds must be broken in the reactants.
Bond breakage requires energy.
Molecules moving too slowly, with too lit
The balanced chemical equation provides information about substances
present at the beginning and end of the reaction.
The reaction mechanism is the process by which the reaction occurs.
Mechanisms provide a pict
Mechanisms with a Slow Initial Step
Consider the reaction:
NO2(g) + CO(g) NO(g) + CO2(g)
The experimentally derived rate law is: Rate = k[NO2]2
We propose a mechanism for the reaction:
Step 1: NO2(g) +
Step 2: NO3(g) +
A catalyst is a substance that changes the rate of a chemical reaction
without itself undergoing a permanent chemical change in the process.
There are two types of catalysts:
Enzymes are biological catalysts.
Most enzymes are large protein molecules.
Molar masses are in the range of 104 to 106 amu.
Enzymes are capable of catalyzing very specific reactions.
For example, catalase is an enzyme fou