Chemistry 18.1
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18.1
Rates of Reaction
The heat given off by the
corrosion reaction of an ironmagnesium alloy with salt
water can produce a hot meal.
The rate of reaction is
increased by adding salt
water, so heat is produced
rapidly. You will learn some
ways in which the rate of a
reaction can be increased.
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18.1
Rates of Reaction
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Collision Theory
Collision Theory
How is the rate of a chemical change
expressed?
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18.1
Rates of Reaction
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Collision Theory
In chemistry, the rate of chemical
change, or the reaction rate, is usually
expressed as the amount of reactant
changing per unit time.
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18.1
Rates of Reaction
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Collision Theory
A rate is a measure of the speed of any change
that occurs within an interval of time.
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18.1
Rates of Reaction
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Collision Theory
Rates of chemical reactions are often measured
as a change in the number of moles during an
interval of time.
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18.1
Rates of Reaction
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Collision Theory
According to collision theory, atoms, ions, and
molecules can react to form products when they
collide with one another, provided that the
colliding particles have enough kinetic energy.
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18.1
Rates of Reaction
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Collision Theory
Effective Collision
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18.1
Rates of Reaction
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Collision Theory
Ineffective Collision
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18.1
Rates of Reaction
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Collision Theory
The minimum energy that colliding particles
must have in order to react is called the
activation energy.
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18.1
Rates of Reaction
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Collision Theory
An activated complex is an unstable
arrangement of atoms that forms momentarily at
the peak of the activation-energy barrier.
The activated complex is sometimes called the
transition state.
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18.1
Rates of Reaction
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Factors Affecting Reaction Rates
Factors Affecting Reaction Rates
What four factors influence the rate of a
chemical reaction?
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18.1
Rates of Reaction
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Factors Affecting Reaction Rates
The rate of a chemical reaction depends
upon temperature, concentration,
particle size, and the use of a catalyst.
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Rates of Reaction
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Factors Affecting Reaction Rates
Temperature
Storing foods in a refrigerator keeps them fresh
longer. Low temperatures slow microbial action.
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18.1
Rates of Reaction
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Factors Affecting Reaction Rates
Concentration
a. In air, a lighted splint glows and soon goes out.
b. When placed in pure oxygen (higher oxygen
concentration), the splint bursts into flame.
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Rates of Reaction
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Factors Affecting Reaction Rates
Particle Size
The minute size of the reactant particles (grain
dust), and the mixture of the grain dust with oxygen
in the air caused the reaction to be explosive,
destroying the grain elevator.
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Factors Affecting Reaction Rates
Catalysts
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18.1
Rates of Reaction
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Factors Affecting Reaction Rates
An inhibitor is a substance that interferes with
the action of a catalyst. Antioxidants and
antimicrobials used in drying fruits and
preserving fruit juices slow the action of microbes
and limit contact with air.
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18.1 Section Quiz.
Assess students’ understanding
of the concepts in Section 18.1.
Continue to:
-or-
Launch:
Section Quiz
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18.1 Section Quiz.
1. The units below that would be appropriate to
measure the rate of a chemical reaction is
a. mmol/s.
b. mol/L.
c. kJ/mol.
d. h/mol.
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18.1 Section Quiz.
2. In a chemical reaction, the energy of reactants
is always
a. greater than the energy of the products.
b. more than the activation energy.
c. less than the activation energy.
d. less than the energy of the products.
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18.1 Section Quiz.
3. An increase in which one of the following will
NOT increase the reaction rate?
a. temperature
b. concentration of reactants
c. total mass of reactants
d. surface area of reactants
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18.1 Section Quiz.
4. A catalyst works because it
a. lowers the activation energy.
b. increases the temperature.
c. is permanently changed in a reaction.
d. supplies energy to a reaction.
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