11

A BALANCED EQUATION

THE HEART OF THE HEART OF STOICHIOMETRYSTOICHIOMETRY

22

Proportional Proportional RelationshipsRelationships

StoichiometryStoichiometry mass relationships between mass relationships between

substances in a chemical reactionsubstances in a chemical reaction based on the mole ratiobased on the mole ratio

Mole RatioMole Ratio indicated by coefficients in a indicated by coefficients in a

balanced equationbalanced equation

2 Mg + O2 Mg + O22 2 MgO 2 MgO

33

Proportional Proportional RelationshipsRelationshipsProportional Proportional RelationshipsRelationships

I have 5 eggs. How many cookies can I have 5 eggs. How many cookies can I make?I make?

3/4 c. brown sugar3/4 c. brown sugar1 tsp vanilla extract1 tsp vanilla extract2 eggs2 eggs2 c. chocolate chips2 c. chocolate chipsMakes 3 dozen cookies.Makes 3 dozen cookies.

2 1/4 c. flour2 1/4 c. flour1 tsp. baking soda1 tsp. baking soda1 tsp. salt1 tsp. salt1 c. butter1 c. butter3/4 c. sugar3/4 c. sugar

5 eggs5 eggs 3 doz.3 doz.

2 eggs2 eggs= 7.5 dozen cookies= 7.5 dozen cookies

Ratio of eggs to cookies

44

HOW TO SOLVE HOW TO SOLVE PROBLEMSPROBLEMS

There are four basic types of There are four basic types of

problems:problems: Mole to moleMole to mole Mole to gramMole to gram Gram to moleGram to mole Gram to gramGram to gram

55

MOLE TO MOLE MOLE TO MOLE PROBLEMSPROBLEMS

X Moles A is the amount given in the problem

Moles A to Moles B is the mole ratio from your equation.

The coefficients are the mole ratio!

X mol A

mol B

mol A= mol B

66

2H2H22 + O + O22 2H 2H22OO

If you have 12 moles of If you have 12 moles of oxygen, how many moles of oxygen, how many moles of water will you make?water will you make?

2 mol H2O

1 mol O2

= 24 mol H2O

(from problem)

12 mol O2

(from equation)

77

You try oneYou try one

Write and balance: Write and balance:

sodium + fluorinesodium + fluorine sodium sodium fluoridefluoride

If you have 5.50 moles of sodium, If you have 5.50 moles of sodium, how many moles of fluorine do how many moles of fluorine do you need?you need?

88

2Na + F2Na + F22 2NaF 2NaF

If you have 5.50 moles of sodium, If you have 5.50 moles of sodium, how many moles of fluorine do how many moles of fluorine do you need?you need?

5.50 mol Na 1 mol F22 mol Na

= 2.75 mol F2

(from problem) (from equation)

99

MOLE TO GRAM MOLE TO GRAM PROBLEMSPROBLEMS

You have to find the molar mass You have to find the molar mass of compounds to solve these of compounds to solve these problems.problems.

X mol A

mol B

mol A

(from problem) (from equation)

grams B

1 mol B

(from periodic table)

= grams B

1010

2Na + F2Na + F22 2NaF 2NaF

If you have 18 moles of fluorine, how If you have 18 moles of fluorine, how many grams of NaF will you make?many grams of NaF will you make?

First, find the g/mol of your First, find the g/mol of your compoundcompound

Then, set up your problem.Then, set up your problem. You must use labels in the problem!!You must use labels in the problem!! Check your sig figs!Check your sig figs!

1111

Find the mass of NaF, Find the mass of NaF, then then

set up the problemset up the problem23g Na + 19g F = 42g/mol NaF23g Na + 19g F = 42g/mol NaF

18 mol F2

(from problem)

(from equation)

(from periodic table)

2 mol NaF

1 mol F2

42 g NaF

1 mol NaF= 1500 g NaF

1212

2Na + F2Na + F22 2NaF 2NaF

If you have 25.0 moles of Na, how many If you have 25.0 moles of Na, how many grams of fluorine will you need?grams of fluorine will you need?

25.0 mol Na 1 mol F25.0 mol Na 1 mol F22 38g F 38g F22

2 mol Na 1 mol F2 mol Na 1 mol F22

(from problem) (from problem) (from equation) (from periodic table)(from equation) (from periodic table)

= 475 g F2

1313

GRAM TO MOLE GRAM TO MOLE PROBLEMSPROBLEMS

You have to find molar mass of You have to find molar mass of compounds to solve these problems, compounds to solve these problems, too.too.

gram A 1 mol A mol B gram A 1 mol A mol B

gram A mol Agram A mol A

(from problem) (from periodic table) (from equation)(from problem) (from periodic table) (from equation)

= mol B

1414

4K + O4K + O22 2K 2K22OO

If you have 245g K, how many If you have 245g K, how many moles of Kmoles of K22O will you produce?O will you produce?

245g 245g KK

1 mol K

39 g K

2 mol K2O

4 mol K= 3.14 mol K2O

1515

GRAM TO GRAM GRAM TO GRAM PROBLEMSPROBLEMS

These are the longest problems of These are the longest problems of all. all.

You have to find the molar mass You have to find the molar mass of several compounds to solve of several compounds to solve the problems.the problems.

You must have labels in every You must have labels in every part of your equation!part of your equation!

1616

GRAM TO GRAM GRAM TO GRAM PROBLEMSPROBLEMS

Now is not the time to take Now is not the time to take shortcuts! I will mark them shortcuts! I will mark them wrong!wrong!

Do not combine any equalities or Do not combine any equalities or skip any equalities.skip any equalities.

My way is the only way! My way is the only way!

1717

GRAM TO GRAM GRAM TO GRAM PROBLEMSPROBLEMS

X grams A 1 mol A

grams A

(from problem)

(from P.T.)

mol B

mol A

(from equation)

grams B

1 mol B

(from P.T.)

= g B

1818

2NaOH + H2NaOH + H22SOSO44 Na Na22SOSO44 + + 2H2H22OO

If you have 95 grams of sodium If you have 95 grams of sodium hydroxide, how many grams of hydroxide, how many grams of sulfuric acid will you need? sulfuric acid will you need?

First, find g/mol of both sodium First, find g/mol of both sodium hydroxide and sulfuric acid. hydroxide and sulfuric acid.

Na = 23

1 O = 16

1 H = 1

40g/mol

2H = 2

1 S = 32

4 O = 64

98g/mol

1919

The set-upThe set-up

95 g NaOH1 mol NaOH

40 g NaOH

1 mol H2SO4

2 mol NaOH

98 g H2SO4

1 mol H2SO4

= 116 g H2SO4

2020

Use the same information and Use the same information and equation to solve the following:equation to solve the following:

How many grams of each product will be How many grams of each product will be produced? produced?

First, find the molar mass of each product.First, find the molar mass of each product.Na = 2(23) = 46 Na = 2(23) = 46 S = 1(32) = 32S = 1(32) = 32 O = 4(16) = 64 O = 4(16) = 64

142 g/mol142 g/mol

H = 2 (1) = 2H = 2 (1) = 2

O = 1(16) = 16O = 1(16) = 16

18g/mol18g/mol

2121

2NaOH + H2NaOH + H22SOSO44 Na Na22SOSO44 + + 2H2H22OO

95g NaOH 1 mol NaOH 1 mol Na95g NaOH 1 mol NaOH 1 mol Na22SOSO44 142 g Na 142 g Na22SOSO44 = g = g NaNa22SOSO44

40g NaOH 2 mol NaOH 1 mol Na40g NaOH 2 mol NaOH 1 mol Na22SOSO44

95g NaOH 1 mol NaOH 2 mol H95g NaOH 1 mol NaOH 2 mol H22O 18 g HO 18 g H22O O = g = g HH22OO

40g NaOH 2 mol NaOH 1 mol H40g NaOH 2 mol NaOH 1 mol H22OO

2222

SolutionSolution

168.63 g Na168.63 g Na22SOSO44

42.75 g H42.75 g H22OO