Why do most particle crashes do absolutely nothing?
You might think that if your reactant particles hit each other, a reaction should just happen. It doesn’t. Most impacts are useless, and collision theory explains why.
When you use collision theory, you explain reaction speed by looking at particles bumping into each other and asking which of those bumps can actually produce new substances.
For your particles to react, three things must line up at the same time. First, they have to meet at all. Second, the impact must be energetic enough. Third, they must connect in a suitable position. If even one of those is missing, nothing changes.
A successful collision is a particle impact that really leads to products because all the needed conditions are met.
Think of it like trying to log into your phone: you need the device, the battery, and the correct passcode. Having only one or two is not enough. Reactions work the same way.
Start with the most basic condition: your particles must actually collide. If reactant particles never come into contact, there is no chance for old bonds to start changing into new ones.
A collision is the moment when reactant particles come into contact with each other.
The second condition is energy. Some impacts are too weak, so the particles just separate again unchanged. To begin a reaction, the particles need enough energy to start disturbing existing bonds.
Activation energy, written as Eₐ, is the smallest amount of energy your particles need in a collision before a reaction can get started.
Even reactions that give out lots of energy still need that first push. So yes, an exothermic reaction can release energy overall and still refuse to start until enough activation energy is supplied.
A reaction can be energy-releasing overall and still need a starter boost. That catches a lot of people out in tests.
The third condition is orientation. Your molecules are not featureless balls; they have shapes and specific places where bonds can break or form. If they hit at the wrong angle, the right parts do not line up, so the collision fails.
Correct orientation means your particles collide in an arrangement where the parts that need to interact are facing the right way.
Imagine two people trying to connect a charger cable in the dark. Even with enough force, it still will not plug in if the connector is the wrong way round. Particle collisions can fail for the same reason.
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