States that atoms, ions, and molecules must collide in order to react. Collision Theory: States that atoms, ions, and molecules must collide in order to react.

Collision Theory: According to collision theory, particles can react to form products if they collide with enough kinetic energy. Particles that do not have enough energy to react bounce apart unchanged when they collide (no reaction).

When two reactant particles collide, they may form an activated complex. An activated complex is an unstable arrangement of atoms that forms for a moment at the peak of the activation- energy barrier. The activated complex forms only if the colliding particles have enough energy and if the atoms are properly oriented.

Enough energy ? Activation Energy barrier (minimum amount of energy Activated Complex (minimum amount of energy required)

The activation-energy barrier must be crossed before reactants are converted to products.

Remember: An endothermic reaction absorbs heat, and an exothermic reaction releases heat. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

An effective collision of oxygen and hydrogen molecules produces water molecules. Activated Complex 2 H2 + O2 2 H2O

An ineffective collision of oxygen and hydrogen molecules produces no reaction; the reactants bounce apart unchanged. 2 H2 + O2 Activated Complex 2 H2 + O2

Particles must collide with: (Effective collision) Favorable (correct) orientation to form the activated complex (transition state) Sufficient energy to form the activated complex, and overcome the Activation Energy, Ea (minimum amount of energy required for a reaction to occur)

Energy absorbed by reaction Reaction progress Activated Complex Endothermic Reaction Ea Products ∆H Reactants Energy absorbed by reaction