Lesson 18: Rates of Chemical Reactions

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Reactions are where it is at in chemistry.

Textbook Reading:  First part of Chapter 15, sections 15.1-15.6, pp. 531-top of 546.

What controls the rate of chemical reactions?

According to the collision theory, when more atoms and molecules in a system are undergoing collisions, there is a higher chance they will bump together in such a way that a reaction can occur. For a reaction to occur particles must collide with enough energy and in the correct orientation. Even if correctly oriented, not all collisions successfully produce products because not all particles have minimum energy needed for the reaction to occur, or activation energy.

Hank Green of Crash Course Chemistry has a concrete way of explaining collision theory, activation energy, and reaction rate: demolition derby!

Another useful (but not too serious) analogy for increasing the rate of reaction can be found in this TED video: How to speed up chemical reactions (and get a date) by Aaron Sams.

So in summary, to speed up chemical reactions you need to:

1. Shove the reactants together by increasing the pressure.
2. Increase the concentration of the reactants or number of particles.
3. Heat the mixture to increase the energy level and number of collisions.
4. Increase the surface area of the reactants.
5. Add a catalyst to lower the activation energy level to what is available in the system.

We’ll be trying some of these methods in lab.


Edit: I’m adding this video from Mr. Anderson at Bozeman Science, too. He talks about the equilibrium constants.

Please let me know if you have any questions.

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