UNIT VIIStoichiome-treeUnit 7: Lesson 1

STOICHIOMETRY

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

COEFFICIENTS IN A REACTION EQUATION:

2Mg + O2 → 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 O2, 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 + O2 → 2MgOWhat if we multiply the equation by 6.02 x 1023

 2(6.02 x 1023)Mg + (6.02 x 1023)O2 → 2(6.02 x 1023)MgO re-write:

 Everything now is read in terms of moles!

Use mol ratio

VII.1 COEFFICIENTS IN A REACTION EQUATION:

Ex: Consider the reaction equation 2Na + Cl2 → 2

NaCl

How many moles of NaCl are produced when 15 moles of Na are reacted?

VII.1 COEFFICIENTS IN A REACTION EQUATION:Consider the reaction equation:

2C2H6 + 7O2 4CO2 + 6H2O

How many moles of Oxygen are needed to produce 18 mols of CO2?

CHEMICAL 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.

HOW 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 #2

MOLES of MOLES ofCHEMICAL CHEMICAL #1 #2

ALWAYS convert your values into moles ---- then cross the mole bridge!!

TO 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 + Cl2 → 2NaCl

Ex: #2How many grams of potassium chloride, KCl, are produced by decomposing 118 g of potassium chlorate, KClO3?

2KClO3 2KCl + 3O2

TRYC3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l)

A sample of propane is burned, what mass of H2O(l) is produced if the reaction also produces 50.0L of CO2(g) at STP?

Ex: #3

Consider the reaction…4NH3 + 5O2 → 6H2O + 4NO

How many molecules of NH3 are required to react with 3.00 mol of O2(g)?

TRY:

2NH3(g) + NaOCl(aq) → N2H4(g) + NaCl(aq) + H2O(l)

If 1.25 x 104 kg of N2H4 is produced, how many litres of ammonia gas, at STP, is required in the reaction?

STOICHIOMETRY CALCULATIONS INVOLVING MOLAR

CONCENTRATION (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, AgNO3?

Cu(s) + 2AgNO3 Cu(NO3)2 + 2Ag

Ex: #2

For the reaction: Zn + 2HCl → ZnCl2 + H2

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 → ZnCl2 + H2

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 CO2(g) at STP is produced if 2.30 L of 0.5 M HCl reacts with an excess of CaCO3?

NEUTRALIZATION REACTIONS AKA TITRATIONS!

Ex: #1H3PO4 + 2KOH → K2HPO4 + 2H2O

What volume of 0.500 M KOH is required to react with 125mL of 0.300 M H3PO4 in order to produce a solution of K2HPO4?

TRY: ANOTHER NEUTRALIZATION REACTIONEx: #2

H3PO4 + 2KOH → K2HPO4 + 2H2OIf 19.8 mL of H3PO4 with an unknown molarity react with 25.0 mL of 0.500 M KOH, according to the above reaction, what is the molarity of the H3PO4?

HOMEWORK

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

24.