 Hi students, welcome to year 12 chemistry and module 5 on equilibrium and acid reactions This is video number 5 looking at and a slightly more deeper analysis of chemical equilibria So what we want to try and do now is see if we can link these ideas of collision theory and reaction rate in order to Help us understand what's going on in an equilibrium system. So firstly, let's just recall that definition of Collision theory, which is that for a reaction to occur particles must collide with sufficient energy to break the bonds and have the appropriate Orientation to allow the new bonds to form. So this is about sufficient energy and Appropriate orientation and we'll look at appropriate orientation a little bit later in a in a subsequent video But for the moment, I want to concentrate on the idea of sufficient energy So we know that sufficient energy is Equivalent to the energy of activation. Okay, so that's one of the things that we've looked at from a year 11 course we know that the energy of activation is the Difference between where the reactants are and the top of this Energy hill so that represents our energy of activation. Now, of course now that we're looking at Reversible reactions or reactions where an equilibrium is established We need also realize that the reaction path doesn't just go in a single direction But can also go in the opposite direction and of course in the opposite direction the energy of activation for a reaction here Which is? endothermic That is the reactants are at the product Sorry are at a higher energy level than the reactants then we have an endothermic reaction and notice that as we go back from the Direction in the direction of y to x so we're going in the reverse direction the energy of activation is now much smaller So for the endothermic reaction, we have a smaller EA Now this is always the case because when we go from y to x this is an exothermic reaction and So therefore now the what was the reactant is now the product and it's at a lower energy level So therefore energy must have been released These energy diagrams show us the relationship between Something which is endothermic in the forward direction then becoming Exothermic in the reverse direction and you can see the difference between the activation energies in each of these cases