Collision theory

Collision theory

1. Reactions happen if particles collide, so if you increase the number of collisions, the reaction happens more quickly. there are 4 factors that all lead to more collisions:

   • Temperature, concentration, the presence of a catalyst and the size of the particles

2. Temperature

   • Increasing the temperature means the particles are going faster and have more energy
     • If the temperature is increased: the reactant particles move more quickly they have more energy the particles collide more often, and more of the collisions result in a reaction the rate of reaction increases
     • Higher temperatures also increase the energy of the collisions since the particals are moving faster. reactions only happen if the particles collided with enough energy. at a higher temperature there'll be more particles colliding with enough energy to make the reaction happen.

3. Concentration

   • Increasing the concentration ( or pressure ) means the particles are more crowded together
     • If the concentration of a dissolved reactant is increased, or the pressure of a reacting gas is increased: the reactant particles become more crowded there is a greater chance of the particles colliding the rate of reaction increases

4. Size of particles

   • The rate of a chemical reaction can be raised by increasing the surface area of a solid reactant. This is done by cutting the substance into small pieces, or grinding it into a powder.
     • Smaller solid particles ( or more surface area) means other particles can get to it more easily
   • If a solid reactant is broken into small pieces or ground into a powder: its surface area increases more particles are exposed to the other reactant there are more collisions the rate of reaction increases
     • For Example : calcium carbonate + hydrochloric acid = calcium chloride dioxide + water
       • Calcium carbonate is the chemical name for marble, you can change the surface area by breaking large marble chips into small chips
   • Fine powders of combustion materials dispersed in the air burn very very fast because they have such a big surface area, if they spark they will explode
     • Explosions are very fast reactions in which a lot of gaseous product is released very quickly. For example: burning hydrogen explosions from TNT or dynamite

5. Catalysts

   • A catalyst is a substance that can increase the rate of a reaction, without being chemically changed or used up in the reaction, and because it isn't used up you only need a tiny bit of it to catalyst large amounts or reaction
   • Catalyst are very specific, they only work in certain reactions
     • eg: iron, making ammonia from nitrogen and hydrogen
   • A catalyst works by giving the reaction particles a surface to stick to where they can bump into each other, and reduces the energy needed by the particles before they react.
     • The number of collisions is NOT increased but there are just more successful collisions

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