Activation Energy
This animation follows the energy profile for both an endothermic and an exothermic reaction. Select
different areas on the energy profile to view the reaction progress on a molecular level.
1) Endothermic Reaction
The animation starts with an energy profile for the reaction
NO + Cl2  NOCl + Cl
You can select four points on the energy profile (A, B, C, and D). At each point, the molecular
changes occurring in the reaction will be shown below the energy profile.
[A]:
As the two molecules approach each other, an attractive force begins to form between the
nitrogen of NO and one of the chlorines of Cl2 (indicated by a dashed line). The bond between
the chlorines begins to weaken (bond length increases).
[B]:
When molecules collide, they form an activated complex -- a temporary species formed by the
reactant molecules as a result of the collision before they form the product. In this reaction, the
activated complex is NOCl2.
[C]:
At this point, the bond between nitrogen and chlorine continues to strengthen and the bond
between the two chlorines continues to weaken.
[D]:
A bond has now formed between nitrogen and chlorine. The bond between the two chlorines
has broken. The products of the reaction are NOCl and Cl.
2) Exothermic Reaction
The animation starts with an energy profile for the reaction
NO2 + CO  NO + CO2
You can select four points on the energy profile (A, B, C, and D). At each point, the molecular
changes occurring in the reaction will be shown below the energy profile.
[A]:
As the two molecules approach each other, an attractive force begins to form between one of the
oxygens of NO2 and the carbon of CO (indicated by a dashed line). The bond between nitrogen
and oxygen of NO2 begins to weaken (bond length increases).
[B]:
When molecules collide, they form an activated complex--a temporary species formed by the
reactant molecules as a result of the collision before they form the product. In this reaction, the
activated complex is NO2CO.
[C]: At this point, the bond between carbon and oxygen continues to strengthen and the bond
[D]: A bond has now formed between carbon and oxygen. The bond between nitrogen and oxygen
has broken. The products of the reaction are NO and CO 2.