hey it's professor Dave, let's learn how to balance equations when substances interact and chemistry occurs we can describe the process using something called a chemical equation. for example when sodium metal reacts with chlorine gas you get sodium chloride or table salt. the arrow here is what separates the reactants, the things that react from the products, the things that you get. the arrow also shows the direction of the reaction. when you see a chemical reaction it describes the substances involved but if we want to be very accurate we need to balance the equation so that there are the same number of atoms on both sides because atoms won't just appear or disappear they all have to be accounted for. for example in order to make one molecule of sodium chloride we need one sodium atom and one chlorine atom. but chlorine gas molecules have two atoms of chlorine each so one molecule of chlorine gas will react with two sodium atoms to give two molecules of sodium chloride. we need to include coefficients before each substance to indicate how many of each we need to make the equation balanced. let's make the distinction that these subscripts tell us how many atoms of a given element are in one molecule, whereas these coefficients tell us how many of that molecule there are. in the reaction where hydrogen gas and oxygen gas go to make water we can see that the gases have two atoms each and water has two hydrogen atoms and one oxygen atom we will need to combine the substances in this ratio to make this equation balanced. now there are the same number of hydrogen and oxygen atoms on both sides of the equation even though they have rearranged their combinations. so if we have an unbalanced equation like this one that we need to balance there's an easy way to do it. we will balance things one element at a time. if an element exists by itself do that one last. start with an element that is present in just one compound on each side let's do carbon first on the left there are three carbon atoms for every molecule of propane and on the right there is just one for every molecule of carbon dioxide so according to the carbons we're going to make three CO2's with every propane. let's put a three there. now the carbons are balanced, three carbon atoms on each side. next let's do hydrogen. there's eight on the left and two on the right, that means we will make four waters with every propane. now hydrogen is balanced eight on each side. last is oxygen. on the right there's six from CO2 and four from water for a total of 10, that means we will need five molecules of 02 to get 10 oxygen atoms on the left side. now the equation is balanced. there is the same number of each type of atom on both sides showing us the correct ratio in which these molecules will have to react. these coefficients are going to be very important as we move forward as we will have to be able to balance equations to make predictions about chemistry let's check comprehension thanks for watching guys. subscribe to my channel for more tutorials and as always feel free to email me