 The one thing just to quickly look at before we finish this video is this area of stereochemistry. We've got to remember that we are dealing with three dimensional collisions and this is what makes life very difficult because we're trying to model processes in two dimensions that are actually occurring in three. One of the things that's important in collisions is not just how often they occur or how much energy they have but also the orientation. So you can see here we've got a collision between a particle of hydrogen and chlorine, so hydrogen chloride and here a double bonded hydrocarbon. This one is ethene. Now in this region here we have a very high density of electrons, so a very strong electronegative region. For this molecule we have polarity. The polarity is created by the greater electronegativity of the chlorine than the hydrogen which means we get a slightly negative, slightly positive region happening here. Over here slightly positive, slightly negative. You can see for the one that we've said will provide a successful collision reaction is where this very negative region of concentrated electrons is hit by this positive region where the hydrogen is coming in. Two negative regions effectively running into each other or coming in from the side and these bonds here are non-polar and so there be no interaction between them. This additional factor can affect collisions as well. It can not just be a factor of how many particles and how much energy the particles have but also the orientation of those particles and how they approach one another as to whether the reaction occurs. So hopefully this gives you a little bit of an idea of some of the ways that we can use our understanding of particles and collisions of those particles to relate to chemical reactions and specifically equilibrium. Thanks for watching.