basic introduction to Stoichiometry I will teach you all the important stoichiometric conversions using Matrix firstly let me teach you that what is stoichiometry well the word strike you means element and the word metri means measurement so Stoichiometry is the calculation of products and reactants and a chemical reaction for example consider this general chemical reaction with the help of Stoichiometry we can find the number of moles of reactants and the number of moles of products so remember that Stoichiometry is the calculation of products and reactants and a chemical reaction now let me teach you the important concept of coefficients and a chemical reaction which a lot of students are not understanding for example consider this chemical reaction hydrogen gas react with nitrogen gas to form a ammonia NH3 now I will balance this chemical reaction there are two hydrogen atoms in the reactants well there are three hydrogen atoms in the products I place two with products and three with the reactants now three n two two is equal to 6 atoms 2 into 3 is equal to 6 atoms there are two nitrogen atoms and there are also two nitrogen atoms so this is complete balanced chemical reaction now these three with hydrogen gas is known as coefficient of hydrogen gas secondly this one with nitrogen gas is known as coefficient of nitrogen gas while these two with NH3 is known as coefficient of NH3 here I will teach you three different stories of coefficients firstly the coefficients represents the amount of substances for example this three coefficient of hydrogen gas shows 3 moles of hydrogen gas one coefficient of nitrogen gas represents one mole of nitrogen gas and two coefficient of NH3 represents 2 moles of NH3 secondly coefficients represent a ratio of reactants to products for example I write hydrogen gas ratio to nitrogen gas to NH3 we know that the coefficient of hydrogen gas is 3 that of nitrogen gas is 1 and that of NH3 is 2. hence this is the ratio of reactants to products thirdly coefficients represents number of molecules let I write three hydrogen gas one nitrogen gas two NH3 now this three coefficient of hydrogen gas represents three molecules of hydrogen gas this one coefficient of nitrogen gas represents one molecule of nitrogen gas and these two coefficient of NH3 represents two molecules of NH3 just remember that Story 1 tells that the coefficient represents the number of moles Story 2 tells that the coefficient represents the ratio of reactants to the products Story 3 tells that the coefficient represents the number of molecules now how can we use these stories to calculate the amount of reactants and products well consider this question how can you form six molecules of NH3 the answer is simple according to the Second Story the ratio of hydrogen to nitrogen to NH3 is three to one one to two we need 6 molecules of NH3 I just multiply 2 N to 3 I also multiply the ratio of n 2 by 3 and that of H2 by 3 now 2 and 2 3 is equal to 6 1 into 3 is equal to 3 3 into 3 is equal to 9. this reveals that we need 9 molecules of hydrogen gas to react with three molecules of nitrogen gas in order to form six molecule of NH3 let me repeat this important statement we need 9 molecules of hydrogen gas to react with three molecules of nitrogen gas in order to form six molecules of NH3 to conclude this whole concept any coefficient and a reaction shows either number of moles a ratio or number of molecules and snorted down all these important Concepts now let me teach you the different conversions of Stoichiometry like mold to mole conversion consider this problem how many moles of nitrogen gas is needed to react with 13.5 moles of hydrogen to form NH3 well I Write the balanced chemical reaction we know that hydrogen gas plus nitrogen gas react together to form NH3 I put here 3 1 and 2. this is the complete balanced chemical reaction now according to the given statement 13.5 moles of hydrogen gas is given we need to find the number of moles of nitrogen gas although there are several ways to calculate it but I will teach you my way to calculate such type of questions firstly I write ratio of hydrogen to the ratio of nitrogen gas we know that it is three to one now listen carefully we are already given the number of moles of hydrogen I will write this 13.5 moles below the hydrogen gas let me repeat it we are already given the number of moles of hydrogen gas I will write this 13.5 moles below this hydrogen gas here if three moles of hydrogen gas react with one mole then 13.5 moles of hydrogen gas react with X moles now I will just cross multiply them 3 into X is equal to 1 into 13.5 I divide both sides by 3 after calculation I get X is equal to 4.5 moles this we need 4.5 moles of nitrogen to react with 13.5 moles of hydrogen hence noted down this important conversion secondly consider this problem how many moles of sulfur trioxide will form when 8.5 moles of sulfur dioxide react with oxygen firstly I Write the balanced chemical reaction according to the given statement sulfur dioxide plus oxygen gas react together to form sulfur trioxide now two oxygen atoms plus two oxygen atoms is equal to four oxygen atoms while in the products there are three oxygen atoms I place here too and the product there are two sulfur atoms in the reactant I plus here too hence this is the complete balanced chemical equation according to the given statement 8.4 moles of sulfur dioxide will react with oxygen to form X moles of sulfur trioxide now I will use my personal way to calculate the number of moles of sulfur trioxide I established ratio between sulfur dioxide and sulfur trioxide we can see that it is 2 ratio to 2 the number of moles of sulfur dioxide is 8.4 moles we need to calculate the number of moles of sulfur trioxide let it is X now I cross multiply them 2 into X is equal to 2 into 8.4 I divide both sides by 2 after calculation I get 8.4 moles thus 8.4 moles of sulfur dioxide will react with excess of oxygen to form 8.4 moles of sulfur trioxide hence noted down this important problem the second type of stoichiometric conversion is mole to gram conversion for example consider this problem firstly I write the complete balanced chemical reaction according to the given statement propane c3h8 react with oxygen to form carbon dioxide plus water it is a simple combustion reaction now there are three carbons in the reactants and one carbon and the products I plus here 3 there are 8 hydrogen in the reactants and two hydrogen in the products I place here for 2 into 4 is equal to 8 hydrogen atoms now 2 and 2 3 is equal to 6 oxygen atoms plus four oxygen atoms is equal to 10 oxygen atoms I write here 5 hence this is the complete balanced chemical equation now four moles of propane will react with oxygen to form X grams of carbon dioxide Alto there are several ways to calculate it but I will use my personal way I solve this type of problem in two steps in the first step I find the number of moles of unknown species like carbon dioxide I establish relationship of ratio between propane and carbon dioxide we can see that it is one two three four moles of propane is given and the moles of carbon dioxide is unknown I have to cross multiply them 1 into X is equal to 4 into 3 after calculation I get X is equal to 12 moles of carbon dioxide hence four moles of propane will react with oxygen to form 12 moles of carbon dioxide let me repeat it four moles of propane will react with oxygen to form 12 moles of carbon dioxide and the Second Step I just convert the number of moles to grams the number of moles of carbon dioxide is 12 moles which we calculated now the molar mass of carbon dioxide is 44 gram to convert the number of moles of carbon dioxide to grams I use this formula number of moles into molar mass we know that the number of moles of carbon dioxide is 12 moles and two the molar mass of carbon dioxide is 44 gram after calculation I get 528 grams of carbon dioxide therefore we say that 4 moles of propane will react with oxygen to form 528 grams of carbon dioxide in such type of problems I convert given number of moles to moles of unknown species then I convert number of moles to grams hence noted down this important conversion the third type of stoichiometric conversion is grams to mole conversion consider this problem how many moles of hydrogen are necessary to react with 6 gram of nitrogen to produce NH3 well as usual I write balanced chemical chemical reaction hydrogen gas plus nitrogen gas will react together to form NH3 I put here 3 1 and 2. this is the complete balanced chemical equation to solve this type of stoichiometric problems I follow two steps in the first step I convert the given Mass to mole of the known species for example 6 gram of nitrogen gas is given and we have to find X moles of hydrogen gas we know that the given mass of nitrogen gas is 6 gram and the molar mass of nitrogen gas is 28 gram now I will use this formula to find the number of moles of nitrogen gas given Mass upon molar mass the given mass of nitrogen is 6 gram and the molar mass of nitrogen gas is 28 gram after calculation I get 0.23 moles of nitrogen gas and 6 gram are 0.23 moles of nitrogen gas react with X mole and the Second Step I will find the number of moles of unknown species like hydrogen gas I establish relationship of ratio 2 between hydrogen gas and nitrogen gas it is three to one we know that 0.23 moles of nitrogen gas react with X moles of hydrogen gas I cross multiply them 1 and 2x is equal to 3 and 2 0.23 after calculation I get X is equal to 0.69 moles of hydrogen gas therefore 6 gram of nitrogen gas will react with 0.69 moles of hydrogen gas to produce NH3 in such type of problems I convert given Mass to number of moles then I convert number of moles to number of moles of unknown species hence noted down this important conversion lastly let me teach you grams to grams conversion for example consider this problem how many grams of oxygen react with 10 grams of hydrogen gas to form H2O well as usual I write the complete balanced chemical equation hydrogen gas plus oxygen gas react together to form water I write 2 1 and 2. now it is a complete balanced chemical reaction here the mass of hydrogen gas is given which is 10 grams I need to find the mass of oxygen gas also I need to find the number of moles of hydrogen gas and oxygen gas firstly I find the molar mass of hydrogen gas oxygen gas and H2O the molar mass of hydrogen gas is 2 gram that of oxygen gas is 32 gram and that of water is 18 Gram now I will follow these three steps to solve such type of problems in the first step I will find number of moles of non-specy like hydrogen gas I use this formula number of moles of hydrogen gas is equal to given Mass upon molar mass the given mass of hydrogen gas is 10 gram and its molar mass is 2 gram after calculation I get 5 moles of hydrogen gas thus 10 gram are 5 moles of hydrogen gas react with X grams of oxygen and the Second Step I find the number of moles of unknown species like oxygen gas to do so I establish relationship of ratio between hydrogen gas and oxygen gas we know that it is two to one also we know that 5 moles of hydrogen gas react with X moles of oxygen gas now I cross multiply them 2 into X is equal to 1 into 5. after calculation I get 2.5 moles hence 5 moles of hydrogen gas react with 2.5 moles of oxygen gas now I will convert 2.5 moles of oxygen gas to grams and the third step I convert the number of moles to grams to do so I use this formula mass of oxygen gas is equal to number of moles and to molar mass the number of moles of oxygen gas is 2.5 and its molar mass is 32 grams after calculation I get 80 grams of oxygen in case therefore 10 grams of hydrogen gas react with 80 grams of oxygen gas to produce H2O in such type of problems remember these three steps firstly I convert given Mass to number of moles secondly I convert number of moles to number of moles of unknown species thirdly I convert number of moles to grams I hope that you have learned all about basic stoichiometry