this is going to be our last lecture in the chemical kinetics catalysis. So what is catalysis? It's basically making a reaction. Go faster and catalysis, gets into the reaction and gets out off the reaction without being consumed. So how does that happen? So let's say we have this reaction. All three plus oxygen goes through til ity and we have this graph. This is energy versus progress. So we have this activation energy for all. Triano is quite high. So this reaction is going thio happen. But it's going to be really slow. So instead off that we can make this direction go faster. How we can do that is if we have c l plus all tree C l o plus o two and Cielo plus O C l plus O two, whatever you're going to get in the overall is left hand side, right hand sides again. This guy's cancel. These guys canceled. So we have or three plus O goes to chill too. Now, do you remember the intermediates? Cielo? This isn't the products. In the first step, reacting in the second step gets consumed. We don't see that. So Cielo is our reaction. Intermediate however cl we see it in the reactant and then we see it in the products. So what happens here? We have the CL in the product and in the next cycle it gets back in because reaction with old poultry, you get everything and then gets up and then again gets back. And then again it gets back. We call these substances catalysts, and if you want to look at this graph off, how this works is normally this energy off activation for the very first and overall energy overall reaction is quite high. We need to bring this energy down. So once you add the chloride, what happens is this big energy is getting broken down to two smaller energies, and going uphill from here is very easier than going uphill from there. So there's going to be a faster reaction. That's why we're using catalysts. And lastly, what we have is the enzymes. So we have this model that we call locking key, and let's try to show it this way. Let's say we have something like that. Let's say this is our n science and let's say we have a substrate that looks like this so What will happen is this guy enzyme and substrate needs and it gives us the enzyme substrate complex. And after that are enzymes stays the same, but our substrate iss from this site broken apart. And then we can use this enzyme over here again to meet another substrate. So this cycle goes on and on, and then basically, that's what happens in our body. So for writing it mathematically, what we have is mhm plus s is in equilibrium with E s, and those are fast step and then e s goes to enzyme and product, and this is a slow step.