Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
163
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 16
1. Calculate the average reaction rate over 150 s expressed in
terms of the disappearance of Br 2 .
2. Calculate the average reaction rate over 150 s expressed in
terms of the appearance of HBr.
3. Explain the difference between the rate calculated in problem 2
and the rate calculated in problem 1.
Collision Theory What must happen in order for substances to
react? According to the collision theory, atoms, ions, and molecules
must collide with each other in order to react. The following three
statements summarize the collision theory.
1. Particles must collide in order to react.
2. The particles must collide with the correct orientation.
3. The particles must collide with enough energy to form an unstable activated complex, also called a transition state, which is
an intermediate particle made up of the joined reactants.
The minimum amount of energy that colliding particles must have in
order to form an activated complex is called the activation energy
of the reaction. Particles that collide with less than the
activation energy cannot form an activated complex.
16.2 Factors Affecting Reaction Rates
Other than the requirement that substances must be able to react,
what conditions affect the rates of chemical reactions? Recall the
collision theory. In order to react, particles of reactants must have an
opportunity to collide, they must collide in the right orientation, and
they must collide with enough energy to form an activated complex.
Surface Area One way to increase the opportunity for collisions
is to increase the surface area of a solid reactant. For example, a
solid chunk of iron will rust slowly, but the same amount of iron
made into extra-fine iron wool will rust so rapidly in moist air that it
gives off heat.
Concentration Increasing the concentration of one or more
reactants puts more particles of the reactants in the same space,
thereby increasing the frequency of collisions. The extra-fine iron
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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
163
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 16
1. Calculate the average reaction rate over 150 s expressed in
terms of the disappearance of Br 2 .
2. Calculate the average reaction rate over 150 s expressed in
terms of the appearance of HBr.
3. Explain the difference between the rate calculated in problem 2
and the rate calculated in problem 1.
Collision Theory What must happen in order for substances to
react? According to the collision theory, atoms, ions, and molecules
must collide with each other in order to react. The following three
statements summarize the collision theory.
1. Particles must collide in order to react.
2. The particles must collide with the correct orientation.
3. The particles must collide with enough energy to form an unstable activated complex, also called a transition state, which is
an intermediate particle made up of the joined reactants.
The minimum amount of energy that colliding particles must have in
order to form an activated complex is called the activation energy
of the reaction. Particles that collide with less than the
activation energy cannot form an activated complex.
16.2 Factors Affecting Reaction Rates
Other than the requirement that substances must be able to react,
what conditions affect the rates of chemical reactions? Recall the
collision theory. In order to react, particles of reactants must have an
opportunity to collide, they must collide in the right orientation, and
they must collide with enough energy to form an activated complex.
Surface Area One way to increase the opportunity for collisions
is to increase the surface area of a solid reactant. For example, a
solid chunk of iron will rust slowly, but the same amount of iron
made into extra-fine iron wool will rust so rapidly in moist air that it
gives off heat.
Concentration Increasing the concentration of one or more
reactants puts more particles of the reactants in the same space,
thereby increasing the frequency of collisions. The extra-fine iron
▲
▲
▲