 So by now we have a nice list of factors that we should be able to evaluate. Please look at the depth that's required in a verb like evaluate. You need to make a judgment about these things. So therefore you can present a lot of information but you also need to evaluate and judge which of these factors are really important when you are considering a chemical synthesis process. And in our last one we look at some of these broader issues around environmental, social and economic issues. And in order to do that I thought we'd set this last one in the context of sulfuric acid production. So our final case study is around the production of sulfuric acid. Now sulfuric acid is a really important substance. It's one of those substances that we've used a number of times as a catalyst as it is a really good dehydrating agent. So if we think about things like our esterification process, if we also think about the conversion between ethanol to ethane or ethane to ethanol, these both can use sulfuric acid as a catalyst for the reactions. And so and beyond that of course sulfuric acid has a huge range of applications. The process for producing sulfuric acid in an industrial scale or on an industrial scale is quite complex and has a number of different steps associated with it. The first thing we need to do is we need to extract sulfur from the ground. Usually that's tied up in deposits of metallic ores or it can be found underground and removed in a process known as the fresh process. I'm not going to go into detail on that. There is a bit of information. If you want to have a look at it, it's quite an interesting little process of how we get something like sulfur up from underground and there's a few really important environmental impacts associated with that. Not the least of which is that the sulfur will naturally undergo some of these reactions as it oxidizes in the presence of oxygen. And so we get a few of these interesting little things that are contributors to acid rain in the atmosphere as equally as they are a desired product of sulfuric acid production in an industrial context. The next part is called the contact process and the main reason it's called the contact process is because we use a catalyst in order for the reactants to be in contact with the catalyst to speed up the rate of the reaction and also to control that reaction. Because this is an equilibrium, all of the things that we've previously talked about in terms of temperature and pressure and concentration all affect our yield and also are part of our reaction conditions that we can discuss in terms of sulfuric acid production. Once again, you would need a little more background if you wanted to go into this in detail, but even just being given an equation like this should tell you something about the effect of temperature on a delta H negative. So therefore exothermic process, the effect of pressure where we have two and two plus one is three moles of gases and also how we may or may not be able to remove these. The third step is to turn the sulfur trioxide, the SO3, into sulfuric acid. Now this can be a very dangerous process and so often there's a step in between the conversion of sulfur trioxide and the production of sulfuric acid and that produces another little product called oleum.