Collision Theory

Use the Collision Theory to explain the rate of chemical reactions. Include: Activation energy Draw potential energy diagrams for various reactions. Include: exothermic, endothermic, activated complex, enthalpy Additional KEY Terms transition state

In order for a chemical reaction to occur, the reacting particles must collide with each other. If the particles do not collide, no reaction occurs. The collision theory states:

1. Particles must collide with correct orientation

2. Particles must collide with enough energy: Activation Energy (E A ): Minimum energy needed for a reaction to take place. Energy is required to break old bonds Energy (Potential) is stored within new bonds Colliding particles have Kinetic Energy (velocity) If total energy (PE + KE) ≠ Activation Energy - NO REACTION

Activation Energy Particles with Activation Energy Each reaction has its own specific activation energy. Maxwell-Boltzman Curve Frequency of successful collisions determines the Rate of a reaction.

At point of collision: Particles form unstable intermediate particle called the activated complex or transition state. AC has maximum potential energy but exists for a very small time. + Kinetic Energy Potential Energy Kinetic Energy

Enthalpy (H) is the heat content or total energy possessed by the particles in a system. Energy released or absorbed in a reaction is called the change in enthalpy, ΔH, or heat of reaction. Units of energy are Joules (J). ΔH = H products - H reactants

-ΔH : products have less enthalpy (energy) then reactants. Heat flows out of the system – exothermic. +ΔH : products have more energy than reactants. Heat absorbed into the system – endothermic. ΔH = ΔH = H products - H reactants ΔH = ΔH = H products - H reactants

Reaction coordinate diagram or Potential energy (PE) diagram Represents the PE change during a reaction.

Greater activation energy - slower reaction rate - longer the reaction takes.

2 H 2 + O 2 → 2 H 2 O

CH 3 CH 2 Br + OH − → CH 3 CH 2 OH + Br −

CAN YOU / HAVE YOU? Use the Collision Theory to explain the rate of chemical reactions. Include: Activation energy Draw potential energy diagrams for various reactions. Include: exothermic, endothermic, activated complex, enthalpy Additional KEY Terms transition state