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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. Section 16-1. Expressing Reaction Rates (cont.). Reaction rates are determined experimentally. Section 16-1. Reaction Rates:.

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Section 16-1

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Section 16 1

Expressing Reaction Rates

  • The reaction rateof a chemical reaction is stated as the change in concentration of a reactant or product per unit of time.

Section 16-1


Section 16 11

Expressing Reaction Rates (cont.)

  • Reaction rates are determined experimentally.

Section 16-1


2no 2 g 2no g o 2 g

Reaction Rates:

2NO2(g)  2NO(g) + O2(g)

1. Can measure

disappearance of

reactants

2. Can measure

appearance of

products

3. Are proportional

stoichiometrically


Section 16 12

Section 16.1 A Model for Reaction Rates (cont.)

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

Section 16-1


Collision model

Collision Model

Key Idea: Molecules must collide to react.

However, only a small fraction of collisions produces a reaction. Why?


Collision model1

Collision Model

Collisions must have sufficient energyto produce the reaction (must equal or exceed the activation energy).

Colliding particles must be correctly orientedto one another in order to produce a reaction.


Section 16 13

Collision Theory (cont.)

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

Section 16-1


Activation energy

Activation Energy

The minimum energy required to transform reactants into the activated complex

(The minimum energy required to produce an effective collision)

Flame, spark, high temperature, radiation are all sources of activation energy


Section 16 14

Collision Theory (cont.)

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

Section 16-1


Section 16 15

Collision Theory (cont.)

Section 16-1


Section 16 16

Collision Theory (cont.)

Section 16-1


Section 16 17

Collision Theory (cont.)

Section 16-1


Section 16 18

A

B

C

D

Section 16.1 Assessment

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.

Section 16-1


Section 16 19

A

B

C

D

Section 16.1 Assessment

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

Section 16-1


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