 Hi students, welcome to Year 12 Chemistry and Module 5, Equilibrium and Acid Reactions. This is video number 6, where we start to look at how we can change what's happening in an equilibrium system. So we're going to focus on the effect of temperature, first of all. In order for us to start analyzing these equilibria, what we need to do is realize that there are certain factors that we can change with respect to each of these different equilibrium systems that we've been examining in order to see what happens as a result. Now what we're going to be doing is we're going to be invoking Lyscia-Telier's principle. Lyscia-Telier's principle says when a system in equilibrium is subject to a change in concentration, temperature, external pressure, or some other factor which upsets the equilibrium, the system reacts in such a way as to counteract that change. Basically, if you do something to a system, the system tries to shift in order to undo that change, to reverse what it was that you did. There are three factors which are very important in equilibrium systems, the first of which I have already mentioned, temperature, and that's one that we will have a look at in this particular video. The concentration of both reactants or products can be important as well as the pressure and for gases, the volume specifically relating to gases that are present. When we talk about equilibria, we tend to talk about two different types of equilibria, homogeneous. These are often easier to deal with because say all species are gases. There's ways that we can deal with the fact that all the species are gases and look at them both in terms of their concentration and their pressure or volume. But occasionally we have heterogeneous equilibria. So something where maybe we warm a solid, the solid turns into perhaps another solid and or liquid and or gas. And then we have a combination of different types of states of matter as well as different substances being produced. And this can sometimes make things a little bit easier, sometimes it makes things a little bit more complex.