UNIT VII Stoichiome-tree Unit 7: Lesson 1

S TOICHIOMETRY Stoichiometry : The relationship between the amount of reactants used in a chemical reaction and the amounts of products produced by the reaction

C OEFFICIENTS IN A R EACTION E QUATION : 2Mg + O 2 → 2MgO The coefficient 2, means two magnesium atoms react with one oxygen molecule to produce two molecules of magnesium oxide if you double the amounts of Mg and O 2, what will happen to the amount of MgO??? if you use 10 times the amount of reactants, what will happen to the amount of MgO???

2Mg + O 2 → 2MgO What if we multiply the equation by 6.02 x (6.02 x ) Mg + (6.02 x ) O 2 → 2 (6.02 x ) MgO re- write: Everything now is read in terms of moles! Use mol ratio

VII.1 C OEFFICIENTS IN A R EACTION E QUATION : Ex: Consider the reaction equation 2Na + Cl 2 → 2 NaCl How many moles of NaCl are produced when 15 moles of Na are reacted?

VII.1 C OEFFICIENTS IN A R EACTION E QUATION : Consider the reaction equation: 2C 2 H 6 + 7O 2  4CO 2 + 6H 2 O How many moles of Oxygen are needed to produce 18 mols of CO 2 ?

C HEMICAL EQUATIONS WRITTEN IN TERMS OF MOLES ! A chemical equation is written in terms of moles of reactants and products To predict the moles of each substance, you can use the mole ratio Stoichiometry calculations allow you to calculate the amount of CHEMICAL #1 involved in a reaction, based on the amount of CHEMICAL #2 Connects two different formulas.

H OW TO CONNECT ONE CHEMICAL TO THE OTHER From UNIT 5 ( The Mole Unit), we know how to get from L to moles, g to moles, molecules to moles etc.... MOLES are the way to go from CHEMICAL #1 to CHEMICAL #2MOLES ofCHEMICAL #1 #2 ALWAYS convert your values into moles ---- then cross the mole bridge!!

T O GO FROM ONE CHEMICAL TO THE OTHER … ANYTIME you are asked to calculate a mass, # of molecules, or a volume between TWO chemicals you MUST change it first into moles, second use the mole ratio between these two chemicals you have, then third change back to whatever units the question wants! units you have  moles  mole ratio  units you want

Ex #1: How many moles of sodium metal would be needed to react with chlorine gas and make 737 g of sodium chloride ? 2Na + Cl 2 → 2NaCl

Ex: #2 How many grams of potassium chloride, KCl, are produced by decomposing 118 g of potassium chlorate, KClO 3 ? 2KClO 3  2KCl + 3O 2

TRY C 3 H 8(g) + 5O 2(g) → 3CO 2(g) + 4H 2 O (l) A sample of propane is burned, what mass of H 2 O (l) is produced if the reaction also produces 50.0L of CO 2(g) at STP?

Ex: #3 Consider the reaction… 4NH 3 + 5O 2 → 6H 2 O + 4NO How many molecules of NH 3 are required to react with 3.00 mol of O 2(g) ?

TRY: 2NH 3(g) + NaOCl (aq) → N 2 H 4(g) + NaCl(aq) + H 2 O(l) If 1.25 x 10 4 kg of N 2 H 4 is produced, how many litres of ammonia gas, at STP, is required in the reaction?

S TOICHIOMETRY C ALCULATIONS I NVOLVING M OLAR C ONCENTRATION (M) Molar Concentration: M = mols/L Only use 22.4L/mol if it is a gas at STP So sometimes you use M as a conversion factor!!!

Ex: # 1 If copper wire is put in a solution of silver nitrate, how many grams of copper will react to completely replace silver from 208 mL of 0.100M solution of silver nitrate, AgNO 3 ? Cu (s) + 2AgNO 3  Cu(NO 3 ) 2 + 2Ag

Ex: #2 For the reaction: Zn + 2HCl → ZnCl 2 + H 2 a) What volume of 3.00 M HCl is required to react with 12.35g of zinc?

Ex: #2 (continued) For the reaction: Zn + 2HCl → ZnCl 2 + H 2 b) How many moles of hydrogen are produced when 12.35g of zinc are reacted with the correct amount of HCl?

Ex: #3 Let’s start together What volume of CO 2(g) at STP is produced if 2.30 L of 0.5 M HCl reacts with an excess of CaCO 3 ?

N EUTRALIZATION REACTIONS AKA TITRATIONS ! Ex: #1 H 3 PO 4 + 2KOH → K 2 HPO 4 + 2H 2 O What volume of M KOH is required to react with 125mL of M H 3 PO 4 in order to produce a solution of K 2 HPO 4 ?

TRY : A NOTHER NEUTRALIZATION REACTION Ex: #2 H 3 PO 4 + 2KOH → K 2 HPO 4 + 2H 2 O If 19.8 mL of H 3 PO 4 with an unknown molarity react with 25.0 mL of M KOH, according to the above reaction, what is the molarity of the H 3 PO 4 ?

HOMEWORK Stoichiometry: p. 127 # 6,7,8,9,12 Molar Concentrations: p. 131 # 17, 22, 24.