# STOY-KEE-AHM-EH-TREE It's a big word that describes a simple idea. Stoichiometry: is the part of chemistry that studies amounts of substances that are.

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STOY-KEE-AHM-EH-TREE It's a big word that describes a simple idea. Stoichiometry: is the part of chemistry that studies amounts of substances that are involved in reactions OR… Simply the “math of chemistry”

You might be looking at the amount of material that is produced by the reaction. You might be looking at the amounts of substances before the reaction Stoichiometry is all about amounts.

PRACTICE BREAKDOWN : find the mass for these compounds N2N2 NO 2 2 NH 3 3 (PO 4 ) 3 14 + 14 28 grams 14 + 16 + 16 46 grams 14 + 1 + 1 + 1 17 grams X’s 2 (the coefficient) 17 x 2= 34 grams 31 X 3= 93 285 grams X’s 3 (the coefficient) 285 x 3= 855 grams 16X 12= 192

GOAL – to find the mass of the reactants and the products in a chemical reaction Example: find the mass of each compound or molecule for the following equation N 2 + 3H 2 --- > 2NH 3 ( Reactants ) ( Products ) 28g 6g 34g Both sides must be equal

13 27 20 40

5 11 2) set is up to CANCEL the unit that you want to get rid of Ex: If you have 50 grams of Boron, how many moles do you have? 1 mole=11g 50g1 mole 1g 11g 50 g 11g 4.5 moles =x=

Ex: If you have 80 grams of Sodium, how individual particles do you have? 1 mole=23g 80g 1 mole 23g =x = 481.6 23 = 20.93913 Round to 20.9 Answer 1: 20.9 x 10 23 Answer 2: 2.09 x 10 24 11 23

Ex: If you have 7.8 moles of magnesium, how grams do you have? 1 mole=24g 1 7.8 mole 1 mole 7.8 x 24 1 =x = 187.2grams 12 24

Producing a set quantity of a product using stoichiometry Example: While working for Crest, you are instructed to generate 500grams of sodium flouride, how many grams of each of the reactants (Na & F) will you need? Na + F 2 -------- > NaF Balance First! 2Na + F 2 -------- > 2NaF 46g 38g 84g 38g 84g Step 1 Step 2 Find individual masses

2Na + F 2 -------- > 2NaF 46g 38g 84g Step 4 Find # to multiply by Problem asked you to find how much using 500g of sodium fluoride…so figure out how many times 500 is in NaF and use that number to recalculate the rest 500g ÷84g = 5.95 38 x 5.9546x 5.95 273.7g 226.1g 273.7 + 226.1g = 499.8 which rounds to 500 Step 5 Check your work!

Producing a set quantity of a product using stoichiometry Example: Based on the following problem, if an apple tree produces 800grams of sugar, how many grams of CO 2 were used? 6CO 2 + 6H 2 O -------- > C 6 H 12 O 6 + O 2 Looks already balanced! 264g 108g 84g 92g 84g Step 1 Step 2 Find individual masses Sugar - C 6 H 12 O 6 6CO 2 + 6H 2 O ---- > C 6 H 12 O 6 + 6O 2 180g

264g 108g 372g 192g 372g Step 2 Find individual masses 6CO 2 + 6H 2 O ---- > C 6 H 12 O 6 + 6O 2 180g Step 4 Find # to multiply by Step 5 Check your work! 800g ÷180g = 4.44 Answer for grams of CO 2 = 479.52g

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