Chapter 16: Reaction Rates

CHEMISTRY Matter and Change

• Calculate average rates of chemical reactions from experimental data.

energy: the ability to do work or produce heat; it exists in two basic forms: potential energy and kinetic energy

• Relate rates of chemical reactions to collisions between reacting particles.

SECTION16.1

A Model for Reaction Rates

reaction rate

collision theory

activated complex

activation energy

Collision theory is the key to understanding why some reactions are faster than others.

SECTION16.1

A Model for Reaction Rates

Expressing Reaction Rates• The reaction rate of a chemical reaction is stated

as the change in concentration of a reactant or product per unit of time.

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A Model for Reaction Rates

• Reaction rates are determined experimentally.Expressing Reaction Rates (cont.)

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A Model for Reaction Rates

• Collision theory states that atoms, ions, and molecules must collide in order to react.

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A Model for Reaction Rates

Collision Theory

• An activated complex is a temporary, unstable arrangement of atoms in which old bonds are breaking and new bonds are forming.

SECTION16.1

A Model for Reaction Rates

Collision Theory (cont.)

• The minimum amount of energy that reacting particles must have to form the activated complex and lead to a reaction is called the activation energy.

• High activation energy means that few collisions have the required energy and the reaction rate is slow.

Collision Theory (cont.)

SECTION16.1

A Model for Reaction Rates

SECTION16.1

A Model for Reaction Rates

Collision Theory (cont.)

Collision Theory (cont.)

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A Model for Reaction Rates

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A Model for Reaction Rates

Collision Theory (cont.)

• Are more spontaneous reactions faster than less spontaneous reactions?

• ΔG indicates only the natural tendency for a reaction to proceed—it does not affect the rate of a chemical reaction.

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A Model for Reaction Rates

Spontaneity and Reaction Rate

Which of the following is NOT a requirement for a reaction to occur, according to the collision theory? A. Reacting substances must collide. B. Reacting substances must be in an

exothermic reaction. C. Reacting substances must collide in the

correct orientation. D. Reacting substances must collide with sufficient energy to form an activated complex.

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Section Check

A temporary, unstable arrangement of atoms in which old bonds are breaking and new bonds are forming is called ____. A. reaction complex B. reaction substrate C. activated complex D. activated molecule

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Section Check

Key Concepts• The rate of a chemical reaction is expressed as the rate

at which a reactant is consumed or the rate at which a product is formed.

• Reaction rates are generally calculated and expressed in moles per liter per second (mol/(L ● s)).

• In order to react, the particles in a chemical reaction must collide.

• The rate of a chemical reaction is unrelated to the spontaneity of the reaction.

SECTION16.1

A Model for Reaction RatesStudy Guide

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