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STOICHIOMETRY Mass relationship of reactants and products in a chemical reaction zHydrogen gas + nitrogen gas ----> ammonia gas zQualitative: describes the “nature” of the reactants and products zQuantitative: describes the amounts of reactants and products

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Steps for solving Stoichiometry problems: 1.Write a balanced equation for the question. 2.Understand the mole and molar ratio 3.Convert mass of reactant to moles of reactant. 4.Convert moles of reactant to moles of product. 5.Convert moles of product to grams of product. 6.Pick up the calculator and do the math!!

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How about something a little easier to follow???? Like…………. FOOD!!!!!

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The Stoichiometry of a sandwich….. The SMCHS famous sandwich consists of 2 slices of bread, 2 slices of deli meat, 1 slice of cheese, and 3 slices of pickle. Write an equation for the recipe…... 2 slices bread + 2 slices meat + 1 slice cheese + 3 slices pickle 1 sandwich OR….. OR….. 2B + 2M + 1C + 3P 1B 2 M 2 CP 3 2B + 2M + 1C + 3P 1B 2 M 2 CP 3

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How many SMCHS famous sandwiches can be produced when 8 slices of bread, 8 slices of meat, 4 slices of cheese, and 12 slices of pickles are available? Break it down….. BREAD: 8B = 4 B 2 M 2 CP 3 MEAT: 8M = 4 B 2 M 2 CP 3 CHEESE: 4C = 4 B 2 M 2 CP 3 PICKLES: 12P = 4 B 2 M 2 CP 3 EVALUATION: WE CAN MAKE 4 COMPLETE SANDWICHES!!

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How many of each ingredient is needed to make 10 SMCHS famous sandwiches? BREAK IT DOWN….. BREAD: 10B 2 M 2 CP 3 x (2B / B 2 M 2 CP 3 )= 20B MEAT: 10B 2 M 2 CP 3 x (2M / B 2 M 2 CP 3 )= 20M CHEESE: 10B 2 M 2 CP 3 x (1C / B 2 M 2 CP 3 )= 10C PICKLES: 10B 2 M 2 CP 3 x (3P / B 2 M 2 CP 3 )= 30P THUS: 10 Sandwiches require 20B, 20M, 10C, and 30P

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But what if you ran out of pickles? zPickles would be the LIMITING REAGENT for the sandwiches z In any reaction you will likely have a limiting reagent AND an excess reagent. yToo little of one yToo much of the other

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3 H 2 + 1 N 2 2NH 3 zWhat do the coefficients mean? z3 molecules : 1 molecule : 2 molecules zOR 3 moles : 1 mole : 2 moles

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1N 2 + 3H 2 2NH 3 1 molecules : 3 molecules : 2 molecules 10 molecules : 30 molecules : 20 molecules 100 molecules : 300 molecules : 200 molecules 1 (6x10 23 ) : 3 (6x10 23 ) : 2 (6x10 23 ) 1 MOLE : 3 MOLE : 2 MOLE

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1N 2 + 3H 2 2NH 3 1mole of : 3mole of : 2mole of N 2 molecules H 2 molecules NH 3 molecules This is the MOLAR RATIO allowing you to solve problems dealing with masses of substances!

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1 N 2 + 3 H 2 2 NH 3 If 75g of hydrogen reacts, A) How many g of N 2 reacts? Use the molar ratio!! First convert the grams to moles…… 75g H 2 x 1moleH 2 / 2.02g H 2

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Next use molar ratio….. 75g H 2 x 1mole x 1mole N 2 2.02g H 2 3mole H 2 Now you’ve converted to moles of N 2, make the final conversion into grams!!! 75g H 2 x 1mole x 1mole N 2 x 28g N 2 2.02g H 2 3mole H 2 1mole N 2

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75g H 2 x 1mole H 2 x 1mole N 2 x 28g N 2 2.02g H 2 3mole H 2 1mole N 2 = 346.5g = 350g of N 2

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1 N 2 + 3 H 2 2 NH 3 If 75g of hydrogen reacts, B) How many g of NH 3 are formed? 75g H 2 x 1mole H 2 x 2mole NH 3 x 17g NH 3 2.02g H 2 3mole H 2 1mole NH 3 2.02g H 2 3mole H 2 1mole NH 3 MOLAR RATIO: 3mole H 2 : 1mole N 2 : 2mole NH 3 = 420g NH 3

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Use the same system for these zMass - Volume Stoichiometry yInstead of converting the moles of unknown to grams you convert to volume (L) zVolume - Volume - Stoichiometry yInstead of using the molar ratio you use volume ratio and solve for volume

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