Stoichiometry

Lets think about this H3PO4 + KOH → KH2PO4 + H2O H3PO4 + 3KOH → K3PO4 + 3H2O Each product is useful in their own right We can change what product we get depending on how much KOH we add with relative to H3PO4

So what is it? The relationship between the amount of reactant used in a chemical reaction and the amount of product produced by a BALANCED reaction Think of baking 2 cups of flour 1 egg 3 table spoons of sugar 1 table spoon of baking soda 1 cup of milk

Stoichiometry Reactants and products exist in PROPORTIONAL RELATIONSHIPS! It is just a fancy word saying the mole concept between reactants and products. So we can calculate how much product we produce if we know how much reactant we started with. Or we can find out how much reactant we started with, if we know how much product we produced

Stoichiometry Coefficients tells us how many molecules of each substance we have 2H2 + O2 → 2H2O We have 2 hydrogen gas molecules react with 1 oxygen gas molecule to produce two water molecules HOWEVER, we can write it like this 200H2 + 100O2 → 200H2O

Stoichiometry These are all still balanced In addition, we can have this 1.20 x 1024H2 + 6.02 x 1023O2 → 1.20 x 1024H2O These are all still balanced Remember Avagadros number is the amount of particle/molecules/atoms per mole. 6.02 x 1023 particles = 1 mole 2 mol H2 + 1 mol O2 → 2 mol H2O 2H2 + O2 → 2H2O So we represent our coefficient as moles

Molar Ratio It is our proportional relationship between reactants and product This ratio between the mole coefficient of what we are looking for and the mole coefficient of what is given can be expressed as (Mole’s unknown / mole’s given)

Molar Ratio So if we were looking at the water reaction. We want to know how much water we created and our O2 moles are given, we can put it into a mole ratio 2H2 + O2 → 2H2O 2 mol H2O / 1 mol O2 or 1 mol O2 / 2 mol H2O Unknown chemical amount = what we are solving Given chemical amount = what information did the question already give.

NOTE! It is important to write the chemical formula of the substance that the mole is expressing as we are dealing with more than 1 substance now. 2 mol H2O / 1 mol O2 1 mol O2 / 2 mol H2O

Example - 1 4NH3 + 7O2 → 4NO2 + 6H2O What is the mole ratio of NH3 to O2? NH3 and NO2? NH3 and H2O? These 3 cases all follow the CONSERVATION OF MATTER/ATOM Atoms can neither be produced or destroyed!

Molar Ratio We can do a lot of things Calculate the amount of products formed Calculate the amount of reactants used up The molar ratio is always the same with a BALANCED reaction. Hence why balancing is so important

Example - 2 N2 + 3H2 → 2NH3 If we have 2.00 mol of N2 reacting with H2, how many moles of NH3 will be produced? We have 18.00 mole of H2 reacted with N2, how many moles of NH3 will be produced?

Practice - 1 Page 124 - #1-5

Molar Ratio / Mole Ratio / ? So we call this molar ratio by another name We call it a MOLE BRIDGE because it bridges the different chemical substances together Page 125 of your Hebden has the same diagram! NOTE! We can find anything if we convert to the moles of our given chemical and convert it to the moles of the unknown.

Steps to solving stoichiometry questions Predict the chemical reaction (if the product is not given) Balance the chemical reaction (to find molar ratio) If given an amount in mass/volume/particles, convert to moles of that substance Convert the given chemical to the unknown chemical you are trying to solve by crossing the mole bridge using the molar ratio Convert the amount of moles you found to the mass/volume/particles of the unknown substance

Example - 3 2KClO3 → 2KCl + 3O2 If 1.50 mol of KClO3 decomposes. How many grams of O2 will be produced? If 121.0L of O2 is produced, how many moles of KClO3 were decomposed at STP? We want to produce 2.75 mol of KCl. How many particles of KClO3 would be required?

Example - 4 How many litres of chlorine gas at STP can be liberated (collected) from the decomposition of 64.0g of AuCl3? 2AuCl3 → 2Au + 3Cl2

Example - 5 Calculate the mass of AgCl that can be prepared from 200.0g of AlCl3 and sufficient AgNO3 3AgNO3 + AlCl3 → 3AgCl + Al(NO3)3

Example - 6 How many atoms of Na are required to react completely with 75.0L of chlorine gas at STP? 2Na + Cl2 → 2NaCl

Practice - 2 Page 127-128 - #6-16