STOY-KEE-AHM-EH-TREE It's a big word that describes a simple idea.

STOICHIOMETRY STOY-KEE-AHM-EH-TREEIt'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”

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

STOICHIOMETRY PRACTICE BREAKDOWN: find the mass for these compounds N2 3(PO4) 3 2NH3 14 + 14 31 X 3= 93 14 + 1 + 1 + 1 16X 12= 192 28 grams 285 grams 17 grams NO2 X’s 2 (the coefficient) X’s 3 (the coefficient) 14 + 16 + 16 285 x 3= 855 grams 17 x 2= 34 grams 46 grams

STOICHIOMETRY 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 ( Reactants ) ( Products ) N2 + 3H2 --- > 2NH3 6g 28g Both sides must be equal 34g 34g

MOLES 13 27 20 40 1 atom = 27 amu (atomic mass unit) 27 amu = 1 atom 1mole of Al = 27 grams Al C • .5 mole = 20 grams • 1 mole = 40 grams • 2 mole = 80 grams • 2.5 mole=100 grams ½ or .5 moles = 6.02 divided by 2 = 3.01 x 1023 (remove the exponent to do this)

The following expressions are all EQUAL: 5 11 1 mole = the elements mass # = 6.02 x 1023 B 11 grams = 1 mole = 6.02 x 1023boron atoms MAKING CONVERSIONS: 2 Rules 1) numerator & denominator must be equivalent 2) set is up to CANCEL the unit that you want to get rid of 1 mole=11g Ex: If you have 50 grams of Boron, how many moles do you have? 50g 1 mole 50 g 4.5 moles x = = 11g 1g 11g

11 23 Ex: If you have 80 grams of Sodium, how individual particles do you have? Na 1 mole=23g 80g 6.02 x 1023 80 x 6.02 481.6 x = = = 20.93913 23g 1 mole 23 23g Round to 20.9 Answer 2: 2.09 x 1024 Answer 1: 20.9 x 1023

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

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 + F2 -------- > NaF Step 1 2Na + F2 -------- > 2NaF Balance First! 2Na + F2 -------- > 2NaF Find individual masses Step 2 38g 38g 46g 84g 84g

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 2Na + F2 -------- > 2NaF Find # to multiply by Step 4 38g 46g 84g 500g ÷84g = 5.95 46x 5.95 38 x 5.95 226.1g 273.7g Step 5 Check your work! 273.7 + 226.1g = 499.8 which rounds to 500

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 CO2 were used? 6CO 2 + 6H2O -------- > C6H12O6 + O 2 Sugar - C6H12O6 Step 1 Looks alreadybalanced! 6CO 2 + 6H2O ---- > C6H12O6 + 6O2 Find individual masses Step 2 92g 108g 264g 180g 84g 84g

6CO 2 + 6H2O ---- > C6H12O6 + 6O2 Find individual masses Step 2 192g 108g 264g 180g 372g 372g Find # to multiply by 800g ÷180g = 4.44 Step 4 Step 5 Check your work! Answer for grams of CO2 = 479.52g

STOY-KEE-AHM-EH-TREE It's a big word that describes a simple idea.