hi and welcome to the section of the chemistry tutor in this section we're going to do some problems directly related to what we had just learned in the previous section in the atomic theory of matter so if you haven't watched that section go ahead and watch it right now and then come back and work these problems here because what we're going to do is work these problems using those those laws that we just learned in the previous section so we learned about several things in the previous section some of the most important things you'll understand and need to know in chemistry are the law of conservation of mass which we talked about extensively in the last section the law of definite proportions which we talked about extensively in the last section the law of conservation of mass big picture just means when you have a chemical reaction the mass the total mass of everything you start with must equal the total mass of everything you have after the reaction is done and that's because none of this matter is created or destroyed it's just the atoms have rearranged themselves into different components so when we add up the mass on the left and the right hand side of the reaction or before and after same-same difference it means that the total mass is the same in both cases that's crucial you'll be using that in lots and lots of problems law of definite proportions we talked about that's also another really really important guy what it basically means is if you have a chemical compound like h2o for instance it basically says that the atoms that make up that molecule or that compound they join in very specific ratios and so that guy specifically says that if you take a look at the mass ratio of the different elements present the mass that left for instance the mass of oxygen compared to the mass of hydrogen and a water molecule right and you compare that to different molecules from all around the room or all different water molecules all around the world if it's water then it's going to have the same exact mass ratio in other words the same ratio the elements are combining over and over again h2o it's something you kind of already know before joining in to chemistry but we're going to use it a lot because it turns out that if you just know that simple fact you can do quite a bit of calculations and really understand going on chemically just by knowing those two things and so that's what we're going to do in this section we're going to work a few problems to flex our muscles a little bit make sure we really understand what we're doing so the first problem goes as follows if you heat 1 gram of zinc and 0.2 grams of sulfur in a closed container and then after the reaction proceeds you capture 0.608 grams of zinc sulfide and 0.592 grams of unreacted zinc is this possible so if you notice this is going to happen a lot in chemistry it's never going to tell you use the law of conservation of mass to figure out if this is possible it's never going to tell you use the law of definite proportions to figure out this as possible notice it doesn't tell you any law to use and that's because these laws of chemistry that we've learned are so fundamental that you're expected to know them and apply them to every problem because they obey you know it's like a universal thing these are always going to be true so what we need to do is really read this problem and avoid the temptation to just start adding numbers together and we really need to understand what's happening so that we'll know what to do so let's read it one more time we have one gram of zinc and we heat it with 0.2 grams of sulfur in a closed container so we have a closed vessel nothing can get in nothing can get out we heat the grant the zinc and the sulfur in the container we let the reaction proceed so there's some kind of chemical reaction zinc and sulfur coming together right after it's done we open the container up and we look and we see that we have point six zero eight grams of zinc sulfide and zinc sulfide is a chemical compound when we join zinc and sulfur together and we