[Music] hi and welcome back to three science lessons cold UK by the end of this video you should be able to describe the effect of catalysts on the rate of chemical reactions over the course of this topic we've been looking at the factors that affect the rate of reaction all through the topic we've seen the idea of collision theory this states that chemical reactions can only take place when the reacting particles collide with each other and the collisions must have sufficient energy the rate of a chemical reaction is determined by the frequency of successful collisions in other words the number of collisions per second in the last video we saw that the activation energy is the minimum amount of energy that the particles must have in order to react this graph shows the energy profile for a chemical reaction and we can see the activation energy here so in this video we're looking at how catalysts affect the rate of reaction here's the definition of the catalyst catalysts increase the rate of chemical reactions but are not used up during the reaction now catalysts are really important in chemistry they allow us to carry out reactions quickly without needing to increase the temperature and this saves money and because catalysts are not used up during the reaction we can reuse them again and again if we go back to our energy profile we can see our catalysts work as we said before the rate of the reaction depends on the number of particles but I've got enough energy to cross the activation energy barrier and collide successfully catalysts increase the rate by providing a different pathway for the reaction that's got a lower activation energy and you really need to learn that definition so I'm showing you the effect of a catalyst here as you can see when a catalyst is present the particles require less energy to cross the activation energy barrier this means that more particles can successfully collide per second and that increases the rate of the reaction now there are a couple of key points were catalysts that you also need to learn firstly we do not include catalysts in the chemical equation for reaction but because they're not used up in the reaction catalysts are not a reactant secondly different reactions need different catalysts and lastly enzymes act as catalysts in living organisms and we will see those in much more detail in the biology videos remember you'll find plenty of questions on catalysts in my vision workbook and you can get that by clicking on the link above ok so hopefully now you should be able to describe the effect of catalysts on the rate of chemical reactions [Music]