all right hi your 12s it's mr lim here again and this is our first video on chemical synthesis multi-step reactions all right so what are multi-step reactions they are uh chemical reactions that are completed over multiple steps duh calculations need to be completed over all of the steps and can be done each step individually or as one big combined step okay so we're really dealing with these multi-step reactions in terms of calculations okay you need to recognize that with multi-step equations the stoichiometry works across the equations so horizontally but not from one equation to another so not moving from one equation to another let's go through an example so for this multi-step equation where you're producing ammonia first and then you're producing ammonium nitrate okay what that might mean is that let's have a look one mole of nitrogen gas so nitrogen gas here will produce two moles of ammonia that makes sense right it's not as if all of a sudden as between when you go from that ammonia to this ammonia you lose half of it so you're not going to do a stoichiometry between that two and the one there what it means is that you have two moles of this nh3 and that two moles of that nh3 is going to form two moles of that nh4no3 because there's a one-to-one ratio okay so the idea is that you do not have stoichiometry down you do not have that stoichiometry down the two equations or from one equation to another but you have stoichiometry across the equations okay so let's have a look at another one so say you have 6.3 moles of hydrogen gas will produce 4.2 moles of ammonia and then the 4.2 moles of ammonia doesn't suddenly halve it just goes on and produces 4.2 moles of ammonium nitrate okay so the idea is that you do not have stoichiometry going down a reaction going from one reaction to another okay so if you really felt like it you can combine multi-step equations in a process similar to that of redox half equations by multiplying the equation so that the common product or reactant ends up with the same coefficient okay you have to do this for each equation you want to add in which makes it quite difficult to do for many steps so i'll show you what i mean here so you look at this first one here and the common reactant product is c okay so you've got 3c in the second equation and 1c in the first equation which means that you need to multiply this entire first equation by 3. right so when you do that you do 6 a plus nine oops that doesn't look right plus nine b goes across uh plus uh three c plus d okay so that means i've just put in from these two here that's there because they're multiplied by one i haven't changed anything to them okay goes across to uh what 3c 3c and e okay so then i can cancel out those and now i'm just left with that okay so 6a plus 9b plus a d goes to e right then what i have to do is i say okay well what's my common what's my common reactant and product for this equation that one there and that one there that e there so i have to multiply this entire reaction by 2 okay which means that i'll have end up something like okay 12 a plus 18 b plus 2 d and then i have to add in the stuff from over here right so plus 2 e plus 2 f and then it goes 2 and then what will it go to it will go to 2e 2 e as well as g okay the two e's cancel out right so all you end up is with this right 12 a plus 18 b plus 2 d plus 2 f makes a g okay um so that's the way to do it but that takes a lot of effort so ultimately it would probably just be easier if you were to just do it one by one by one okay so if i said that okay if i have four moles of a right i'm going to make two moles of c if i have two moles of c i'm going to make what uh two over three moles of e then i have two over three moles of e i'm gonna make one over three moles of g okay and so it's a four to one third uh ratio which is i think uh 12 to one ratio okay so that's the way i would do it but you can do it this way if you really feel like it right so for multi-step reactions also the reaction that occurs the slowest produces the least amount of the least amount in the set amount of time is the rate determining step and the whole process will only go as fast as that reaction so i've only seen this once or twice um but the idea is that you when they'll give you information about how fast each reaction is going and then they'll say well um what is the rate determining step it's the slowest one okay so that's just a little bit about multi-step reactions not much um and then we will continue on with rate and yield optimization in the next video adios