lesson
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A wooden match sits safely in a box surrounded by oxygen gas, never catching fire on its own. It only ignites when you strike it against the rough strip with force.
Why do some particles ignore each other while others react in an instant?
The Two Rules of Collision Theory
Around 1916, chemists Max Trautz and William Lewis proposed collision theory to explain chemical reactions: reactant particles must physically collide with each other to form products.
However, bumping into each other is not enough on its own. For a collision to be successful, the particles must collide with sufficient kinetic energy and the correct orientation to break existing bonds.
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What determines whether a collision has enough energy to trigger this change?
Activation Energy
The minimum amount of energy that colliding particles must have to react is called the activation energy (Ea).
Think of activation energy as an energetic hurdle. If particles collide with less energy than Ea, their electron clouds repel each other and they simply bounce apart.
📊Interactive diagram
Evaluating Collisions: A Worked Example
Suppose a reaction between gas molecules has an activation energy of Ea=50 kJ/mol.