4 Factors Affecting Reaction Rates

  • temperature – speeds up (heat) or slows down interaction between particles involved in the reaction
  • stirring – increases interaction between particles involved in reaction
  • surface area of reactants – larger surface area = quicker reaction rate
  • concentration of reactants – higher concentration = quicker reaction rate
  • catalyst and inhibitors

Catalysts

  • catalysts are substances that help a reaction happen faster
  • they are present with the reactants BUT are not used up or consumed in the reaction
  • a catalyst is still present at the end of the reaction
  • A catalyst is like adding a bit of magic to a reaction.
  • Reactions need a certain amount of energy to happen.
  • A catalyst lowers the amount of energy needed so that a reaction can happen easier.
  • A catalyst is about energy; it doesn't have to be another molecule. If you fill a room with hydrogen gas and oxygen gas, very little will happen. If you light a match in that room (or just a spark), all of the hydrogen and oxygen will combine to create water molecules. It is an explosive reaction.

/ → The spark is the activation energy.
  • The energy needed to make a reaction happen is called the activation energy.
  • As everything moves around, energy is needed.
  • The energy a reaction needs is usually in the form of heat.
  • When a catalyst is added, something special happens.
  • Maybe a molecule shifts its structure.
  • Maybe that catalyst makes two molecules combine and they release a ton of energy.
  • That extra energy might help another reaction to occur.
  • catalysts are found in reactions involving living and non living things
  • catalysts are very important to the chemical reactions that happen in our bodies
  • in fact, almost all chemical reactions that take place in our bodies involve special catalysts called enzyme
  • an enzyme is a natural catalyst made by all living things
  • without enzymes many reactions in our bodies would need much higher temperatures… temperatures that could be deadly
  • enzymes are particularly important in helping us break down food so our bodies can use the energy the food provides
  • for example we have an enzyme in our saliva that helps start breaking down food while we chew it (what other action is helping this reaction??)
  • enzymes also help to get rid of harmful wastes from our bodies
  • for example one product of reactions in our cells is hydrogen peroxide
  • H2O2 is a poison … but an enzyme in our bodies called catalase speeds up the breakdown of H2O2 into harmless oxygen and water

Catalyst / Inhibitor

Inhibitors

  • An inhibitor that works exactly the opposite of catalysts.
  • Inhibitors slow the rate of reaction. Sometimes they even stop the reaction completely.
  • You might be asking, "Why would anyone need those?"
  • You could use an inhibitor to make the reaction slower and more controllable.
  • Without them, some reactions could keep going and going and going. If they did, all of the molecules would be used up. That would be bad, especially in your body.