Tuesday 14 December 2010

The difference between yield and rate of reaction

This is bugging me a bit, but I think it boils down to this:

Yield means what percentage of the reaction ends up doing what you want. Remember that if it is a reversible reaction, it can make the product and then undo it again.

Rate of reaction means how fast the reaction goes; how quickly you get what you want.

Questions dealing with pressure be about either:
  • If you increase the pressure you push the particles closer together so that they collide more often and the rate of reaction increases.
  • If you increase the pressure of a reversible reaction involving gases, you favour the direction that goes from more molecules to less molecules. If that is the forward direction, then increasing the pressure will increase the yield.

It is the same with temperature:

  • If you increase the temperature, the particle move faster and so collide more frequently. More collisions reach the activation energy. Hence the rate of reaction increases.
  • If a reversible reaction is endothermic in the forward direction and you increase the temperature, then you will increase the yield.

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