[Music] hi and welcome back to frees science lessons. co.uk by the end of this video you should be able to balance chemical equations lots of students think this Topic's tricky but I'll show you a method that always works before I start I'm going to recap what's meant by a chemical formula as that will help us later this shows the formula of the compound sodium carbonate remember that capital letters tell us that we have an element so you can see that we've got three elements in this compound we've got sodium carbon and oxygen so let's look at the number of atoms of each element the little two on the right of the sodium tells us that we've got two atoms of sodium there's no little number on the right of the carbon so that means we've got one atom of carbon finally the small three on the right of the oxygen tells us that we've got three atoms of oxygen now this brings us to one of the most important rules in chemistry you are never allowed to change the small numbers in a chemical formula as this produces a different molecule I've now put a large three in front of the whole formula so what does that mean well this means that we now have three molecules of sodium carbonate and I'm showing you these here we often use large numbers like this in chemistry and it's perfectly acceptable okay here's here's a chemical reaction calcium plus chlorine makes calcium chloride this is a balanced chemical equation because the number of atoms of each element is the same on both the left hand side and on the right hand side on the left hand side we've got one atom of calcium and we've got two atoms of chlorine and on the right hand side we've also got one atom of calcium and two atoms of chlorine so can you see that this equation is balanced in the exam you could be asked to balance a chem equation so let's see how to do this here's another chemical equation and this one's not balanced we've got sodium plus iodine making sodium iodide the first thing we need to do is count the number of atoms of each element on the left hand side and the rightand side of the equation on the left hand side we've got one atom of sodium and on the right hand side we've also got one atom of sodium so the sodium atoms are balanced let's look at the iodine on the left hand side we've got two atoms of iodine but on the right hand side we've only got one atom of iodine so the iodine atoms are not balanced we need to get one more atom of iodine on the right hand side now remember that we cannot change small numbers so this is not allowed however we are allowed to use large numbers in front of a chemical so if I place a large two in front of the sodium iodide like this I now have two atoms of iodine so now the iodine is also balanced however we've got a problem because now we've got two atoms of sodium on the right hand side but we only have one sodium atom on the left hand side we need to get an extra sodium atom on the left hand side and we can do that by putting a lodge two in front of the sodium like this so now you can see that this entire equation is balanced now I should point out that in the exam you're not normally asked to balance an entire equation usually you're only given one part to balance so I'm going to give you a couple of examples to try yourself now and both of these are very typical of the ones that you could get in your exam here's the first example we've got calcium oxide plus hydrochloric acid produces calcium chloride plus water I'd like you to balance this equation by inserting a large number in the space here you should pause the video now and try this okay as you can see we've got one calcium atom on both the left and the right hand sides so the calcium is balanced we've also got one oxygen on both the left and the right hand sides so the Oxygen's balanced as well however we've got one hydrogen atom on the left hand side and we've got two hydrogen atoms on the right hand side so the hydrogen is not balanced we've also got one chlorine atom on the left and two chlorine atoms on the right so this means that the chlorine is not balanced if we place a large two in the space here then this means that we now have two atoms of high hydrogen and two atoms of chlorine on the left hand side so now this equation is balanced here's a final one for you to try in this reaction we've got ion oxide reacting with carbon monoxide and we're producing ion and carbon dioxide I'd like you to balance the equation by inserting a large number in this space you should pause the video now and try this yourself okay on the left hand side we've got two atoms of ion and three atoms of carbon we've also got six atoms of oxygen in total on the left hand side on the right hand side we've got two atoms of iron one atom of carbon and two atoms of oxygen so we need two more atoms of carbon and four more atoms of oxygen on the right hand side and we can get that by adding a large three in the space like this now we have three atoms of carbon on the right and also six atoms of oxygen so the equation's balanced you'll find plenty more question questions on balance and chemical equations in my revision workbook which you can get by clicking on the link above okay so hopefully now you should be able to balance chemical equations [Music]