quarta-feira, 25 de setembro de 2013

Collision Theory

Today, we will learn about Collision Theory!

Well, before we start, just stop and think about all the reactions that are happening around you in this exact moment. It is impossible! Every second, there are millions of reactions occurring around us.

When we are driving a car for example, we can analyse two different reactions: the gasoline being combusted and the steel being rusted.

Even though, these two reactions happen to be occurring in the same vehicle, one takes longer to be completed than the other.

Scientifically speaking, the combustion of gasoline has a faster reaction rate than the rusting of steel. But what is reaction rate?

Reaction rate is the change in the amount of reactants consumed or products generated over time.

However, this leaves us with a question: Why does some reactions occur faster than others? 

Collision Theory   

Before we answer that question above, we need to know how a reaction occurs. What causes it?

A theory explains that a reaction occur when two particles collide with each other. These particles may be atoms, molecule, or ions. 

This theory is called collision theory. However, does every collision result in a reaction?

The answer for that question is NO, and here is why:

Not every collision between reactants results in a reaction.

For example, in a lab, in 1 mL sample of gas there are several collisions of particles. This number is so high that all gases' reactions would be completed in less than a second. However, gas' reactions actually take a long time to occur.

For a collision between reactants actually result in a reaction, the collision must be effective.

A effective collision, which is the one that forms products, must satisfy two criteria: 

  1. The correct orientation of reactants (collision geometry);
  2. Sufficient collision energy (activation energy, Ea).



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