in this video we're going to talk about mole ratio and we're going to solve some problems related to it but let's understand it first so consider this reaction let's say that nitrogen gas reacts with hydrogen gas to produce ammonia which is uh NH3 and let's balance it so we have two nitrogen atoms on the left side so need to put a two in front of ammonia and now we have six hydrogens on the right side 2 * 3 is six so therefore we need to put a three in front of H2 now the coefficients which are the numbers in front of the reactants and the products gives us the mol ratio between compounds for example notice the numbers 1 3 and two so what this means is that one mole of nitrogen gas reacts equivalently with three moles of hydrogen gas to produce 2 moles of ammonia that's the ratio but it doesn't have to be these numbers for example you could multiply everything by two so therefore 2 moles of nitrogen gas reacts with six moles of hydrogen gas to produce four moles of ammonia likewise three moles of N2 reacts with 9 moles of H2 to produce 6 moles of NH3 now here's a question for you let's say if we have 1.5 moles of N2 how many moles of H2 will react with 1.5 moles of N2 so if you want to find out how many moles of H2 reacts with N2 you can convert it start with what you have so we have 1.5 moles of N2 over one our conversion factor is the mol ratio between N2 and H2 which we can use this so for every one mole of N2 that reacts 3 moles of H2 react with it notice that the moles of N2 cancel so it's going to be 1.5 * 3 which is 4.5 and 4.5 is right in between three and six so that number does make sense because 1.5 is right between 1 and two now let's start with this example propane reacts with oxygen gas to reduce carbon dioxide and water now here's the question how many moles of oxygen gas are required to produce 14 moles of water so feel free to pause the video and work on this example now the first thing we need to do is write a balanced chemical reaction so propane is C3 h8 and it reacts with oxygen gas which is datomic and that's O2 carbon dioxide is CO2 water is H2O so we have three carbon atoms on the left side side so therefore we need to put a three in front of CO2 now notice that we have eight hydrogen atoms on the left to balance the equation we need an equal number of hydrogen atoms on the right side so 2 * 4 is 8 so therefore we need to put a four in front of H2O now notice that we have four oxygen atoms in the four water molecules and six oxygen atoms in the three carbon dioxide molecules so on the right side we have a total of 10 oxygen atoms so what number do we need to put in front of o2 to balance it well 10 / 2 is 5 so we need to put a five in front of o2 to balance the chemical reaction and so now everything is balanced so now at this point we can answer the question how many moles of oxygen gas are required to produce 14 moles of water well let's see if we can ballpark the answer the ratio is 5 to 4 so let's say if we have 10 moles of o2 10 moles of oxygen will react with 8 moles of water if you simply multiply 5 by two and 4 by two if we multiply 5 by three we could say that 15 moles of o2 will react with 4 * 3 that is 12 mol of water now let's multiply this by four 20 mol of o2 will react with 4 * 4 16 moles of water now we're looking for 14 moles of water 14 is right in between 12 and 16 so therefore how many moles of oxygen would give us this so it has to be between 15 and 20 so since 14 is in the exact middle of 12 and 16 then this has to be 17.5 that's going to be our answer but let's prove it so first let's start with what we're given and that's 14 moles of water over one now let's use the conversion factor to convert between H2O and O2 the conversion factor is the mo ratio it's 5 to 4 so you can make this statement 5 mol of o2 is chemically equivalent to four mol of water because for every 5 moles of o2 that react four mol of water will be produced now now since we have moles of water on the top we need to put it on the bottom of the second fraction we want the units moles of H2O to cancel so on top we have to put this part of the conversion factor 5 moles of o2 and so now we just need to do the math so let's get a calculator let's multiply 14 * 5 which is 70 and 70 ID 4 is 17.5 moles of o2 and so what this means is that 17.5 moles of o2 is needed to produce 14 moles of water and it's just math that's what it is now let's move on to our next problem here is another one ammonia NH3 reacts with oxygen gas to produce nitrogen gas and water so here's the first part of the question how many moles of oxygen gas is required to react completely with 11 moles of ammonia so go ahead and take a minute and work on this example so let's write a reaction first so we have ammonia and H3 reacting with oxygen gas producing nitrogen gas which is diatomic like O2 and water so let's Begin by balancing the chemical equation so initially we can see that we have two atoms of nitrogen on the right side so that may indicate that we have to put a two in front of any stram and so we have six hydrogen atoms so we may need a three in front of water so we have six hydrogen atoms on both sides but notice that we have an odd number of oxygen atoms and to balance it we're going to have to put a fraction in front of o2 so this will give us three atoms of oxygen on the left and on the right so to avoid the fraction we can double everything so let's make this a four so if we have four atoms of nitrogen on the left we need to put a two in front of N2 to balance it now we have 12 hydrogen atoms in the left 12 / 2 is 6 so we need six in front of H2O now we have have six oxygen atoms and so we need to put a three in front of o2 because 3 * 2 gives a six and now everything is balanced so now we could start with part A so we have 11 moles of NH3 we need to convert it to the moles of o2 so let's start with 11 moles of NH3 the mol ratio between NH3 and O2 is 4 to 3 so for every four moles of ammonia that reacts three moles of oxygen reacts with it so now we need to put the moles of NH3 on the bottom so we're going to put four moles of NH3 based on that number and three moles of o2 based on this number and so we want the units most M of NH3 to cancel and now we just do the math so it's going to be 11 * 3 which is 33 / 4 so the answer is about 8.25 moles of NH3 now let's move on to Part B how many moles of water are produced in this process so we'll still have 11 moles of so let's convert that to the moles of H2O so let's start with 11 M of NH3 now the mol ratio between NH3 and H2O is 4 to 6 so for every four moles of NH3 that reacts six moles of water are produced so once again let's put the four moles of NH3 on a bottom so that those units will cancel and let's put six moles of water on top based on that number so this is going to be 11 * 6 which is 66 / 4 and so that's 16.5 and this should be NH3 this should be O2 by the way and here we're going to have moles of H2O so 11 mol of ammonia will produce 16.5 moles of water and 11 mol of ammonia will react completely with 8.25 moles of o2 so that's it for this video hopefully this gives you a better understanding of how to solve mol ratio problems and stereometry multim problems for