 Hi students, welcome to year 12 chemistry and module 5 equilibrium and acid reactions. This is video number 8 and we're going to be continuing our look at the three factors that can affect equilibrium systems. This time we're going to be looking at, hopefully it makes sense to understand that changing the volume or changing the pressure is only going to be relevant in systems where the equilibrium involves one or more gases. This is where pressure can make quite a difference and there are a couple of general things that we just need to be aware of. There is obviously a relationship between pressure and volume which we looked at in the year 11 course when we were looking at Boyle's law. So in systems involving gases it's very difficult to affect one of these without affecting the other one of these. If you want to increase the pressure of an equilibrium system involving gases the easiest way to do that is to decrease the volume and vice versa. Now of course we also know that concentration is equal to number of moles over volume so therefore there is potentially going to be an effect of change in the concentration as well when we are making changes in the pressure.