unit vii stoichiome-tree lesson 1. vii.1 c oefficients in a r eaction e quation : stoichiometry :...

UNIT VII

Stoichiome-treeLesson 1

VII.1 COEFFICIENTS IN A REACTION EQUATION:

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

VII.1 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???

VII.1 COEFFICIENTS IN A REACTION EQUATION:

*the balanced equation describes the ratio in which the substances combine

  In terms of MOLES:

2(6.02 x 1023)Mg + (6.02 x 1023)O2 → 2(6.02 x 1023)MgO

  2 mol Mg + 1 mol O2 → 2 mol MgO

  The ratio

VII.1 COEFFICIENTS IN A REACTION EQUATION:

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

NaCl a.)How many atoms of Na are required to react

with 10 molecules of Cl2?

b.) How many moles of NaCl are produced when 15 mol of Na are reacted?

p. 124 #1-5

VII.1 COEFFICIENTS IN A REACTION EQUATION:

Consider the reaction equation:

VII.2 STOICHIOMETRY CALCULATIONS INVOLVING MOLES, MASS, AND GAS VOLUME AND MOLECULES

* 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

VII.2 STOICHIOMETRY CALCULATIONS INVOLVING MOLES, MASS, AND GAS VOLUME AND MOLECULES

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!!

IN OTHER WORDS…

ANYTIME AT ALL, you are asked to calculate a mass, # of molecules, or a volume between TWO chemicals, each on one side of the equation,

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 u have moles mole ratio units you want

VII.2 STOICHIOMETRY CALCULATIONS INVOLVING MOLES, MASS, AND GAS VOLUME AND MOLECULES

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

VII.2 STOICHIOMETRY CALCULATIONS INVOLVING MOLES, MASS, AND GAS VOLUME AND MOLECULES

Ex: #2How many grams of potassium chloride, KCl, are produced by decomposing118 g of potassium chlorate, KClO3?

VII.2 STOICHIOMETRY CALCULATIONS INVOLVING MOLES, MASS, AND GAS VOLUME AND MOLECULES

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?

VII.2 STOICHIOMETRY CALCULATIONS INVOLVING MOLES, MASS, AND GAS VOLUME AND MOLECULESEx: #3

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

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

VII.2 STOICHIOMETRY CALCULATIONS INVOLVING MOLES, MASS, AND GAS VOLUME AND MOLECULESTRY:2NH3(aq) + NaOCl(aq) → N2H4(aq) + 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?

VII.3 STOICHIOMETRY CALCULATIONS INVOLVING MOLAR CONCENTRATION

Molar Concentration:

c = n/V

Only use 22.4L/mol if it is a gas at STP

VII.3 STOICHIOMETRY CALCULATIONS INVOLVING MOLAR CONCENTRATIONEx: # 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?

VII.3 STOICHIOMETRY CALCULATIONS INVOLVING MOLAR CONCENTRATION

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

a) What volume of 3.00 M HCl is required to react with 12.35g of zinc?

VII.3 STOICHIOMETRY CALCULATIONS INVOLVING MOLAR CONCENTRATION

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?

VII.3 STOICHIOMETRY CALCULATIONS INVOLVING MOLAR CONCENTRATION

Ex: #3What volume of CO2(g) at STP is produced if 2.30 L of 0.5 M HCl reacts with an excess of CaCO3?

VII.3 STOICHIOMETRY CALCULATIONS INVOLVING MOLAR CONCENTRATION

TITRATIONS

Definition: a process used to determine the unknown concentration of a solution (SAMPLE) by reacting it with a measured amount of a solution with known concentration (STANDARD) until a desired equivalence point is reached.

Usually, it is an acid-base titration.

VII.3 STOICHIOMETRY CALCULATIONS INVOLVING MOLAR CONCENTRATION

Equivalence Point = Stoichiometric Point

Point in titration where the ratio of the moles of each species involved exactly equals the ratio of the coefficients of the species in the balanced reaction equation

 Ratio of COEFFICIENTS = Ratio of MOLES

PRESENT

@ this point the indicator changes colour

VII.3 STOICHIOMETRY CALCULATIONS INVOLVING MOLAR CONCENTRATION

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?

VII.3 STOICHIOMETRY CALCULATIONS INVOLVING MOLAR CONCENTRATION

Ex: #2H3PO4 + 2KOH → K2HPO4 + 2H2O

If 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?

VII.3 STOICHIOMETRY CALCULATIONS INVOLVING MOLAR CONCENTRATION

TRYH2SO4 + 2NaOH → Na2SO4 + 2H2O

If 20.8 mL of H2SO4 with an unknown molarity react with 23.0 mL of 0.400 M NaOH, according to the above reaction, what is the molarity of the H2SO4?

HOMEWORK

Meaning of coefficients: p. 124 # 2, 3. Stoichiometry: p. 127 # 6,7,8,9,12 Molar Concentrations: p. 131 # 17-24.