StoichiometryStoichiometry StoichiometryStoichiometryNC Essential StandardNC Essential Standard

2.2.42.2.4Analyze the stoichiometric relationships

inherent in a chemical reaction

2

Get a pencil, paper,

calculator and a

periodic table and let’s get

to work.

STOICHIOMETRY

3

Review: Converting grams to moles.

Determine how many moles there are in 5.17 grams of Fe(C5H5)2.

Goal

= moles Fe(C5H5)2

Given

5.17 g Fe(C5H5)2

Use the molar mass to convert grams to moles.

Fe(C5H5)2

2 x 5 x 1.001 = 10.012 x 5 x 12.011 = 120.11

1 x 55.85 = 55.85

mol

g 185.97

g 185.97

mol0.0278

+

1 mole Fe(C5H5)2

4

Review: Converting moles to grams.

Determine how many grams are in 1.5 moles of Fe(C5H5)2.

Goal

= g Fe(C5H5)2

Given

1.5 moles Fe(C5H5)2

Use the molar mass to convert moles to grams.

Fe(C5H5)2

2 x 5 x 1.001 = 10.012 x 5 x 12.011 = 120.11

1 x 55.85 = 55.85

mol

g 185.97

278.96

+

185.97 g Fe(C5H5)2

5

Stoichiometry Uses Mole Ratios

Ratios are found within a chemical equation.

2HCl + Ba(OH)2 2H2O + BaCl2 1 1

2 moles of HCl react with 1 mole of Ba(OH)2 to form 2 moles of H2O and 1 mole of BaCl2

coefficients give MOLAR RATIOS

2mol HCl1mol

Ba(OH)2

2mol HCl2mol H2 O

You can make mole ratios out of any combination of coefficients and formulas. The examples here are just

a few

You can make mole ratios out of any combination of coefficients and formulas. The examples here are just

a few

6

(1-2-3) General Approach For Problem Solving:

1. Clearly identify the Goal or Goals and the UNITS involved. (What are you trying to do?)

2. Determine what is given and the UNITS.

3. Use conversion factors (which are really ratios) and their UNITS to CONVERT what is given into what is desired.

7

Sample problem for setting up a stoichiometric problem.

Sam has entered into a 10 mile marathon. Use ALL of the following conversions (ratios) to determine how many inches there are in the race.5280 ft = 1 mile; 12 inches = 1 ft

1. What is the goal and what units are needed?

Goal = X inches

2. What is given and its units?

10 miles

3. Convert using factors (mole ratios).

10 miles = inches

mile 1

ft 5280

ft 1

inches 12 633600

Given Goal

4 mol N2O5

8

When N2O5 is heated, it decomposes:

2N2O5(g) 4NO2(g) + O2(g)

a. How many moles of NO2 can be produced from 4.3 moles of N2O5?

= moles NO2

4.3 mol N2O58.6

b. How many moles of O2 can be produced from 4.3 moles of N2O5?

= mole O2

4.3 mol N2O5

52

2

ON 2mol

O mol12.2

2N2O5(g) 4NO2(g) + O2(g)4.3 mol ? mol

2N2O5(g) 4NO2(g) + O2(g)4.3 mol ? mol

Mole – Mole Conversions

4 mol NO2

9

When H2O is heated, it decomposes:

2H2O(g) 2H2(g) + O2(g)

a. How many grams of O2 can be produced from 6 moles of H2O?

= g O26 mol H2O 32

b. What mass of water O2 can produced from 2 moles of O2?

= g O2

2 mol O2 72

2H2O(g) 2H2(g) + O2(g)6 mol ? g

2H2O(g) 2H2(g) + O2(g)? g 2 mol

Mole – Mass Conversions

1 mol O 2

32 g O 2

2 mol H2O

1 mol O2

18 g H2O

1 mol H2O

10

When H2O is heated, it decomposes:

2H2O(g) 2H2(g) + O2(g)

a. How many moles of O2 can be produced from 25g of H2O?

= O225 g H2O 0.78 mol

b. How many moles of water O2 can produced from 150 g O2?

= 9.3 moles H2O

150 g O2

2H2O(g) 2H2(g) + O2(g)m25 g ? mol

2H2O(g) 2H2(g) + O2(g)? mol 150 g

Mass – Mole Conversions

1 mol O 2

2 mole H2O

1 mol O2

32 g O2

2 mol H2O

1 mol O2

18 g H2O

1 mol H2O

11

Aluminum is an active metal that when placed in hydrochloric acid produces hydrogen gas and aluminum chloride. How many grams of aluminum chloride can be produced when 3.45 grams of aluminum are reacted with an excess of hydrochloric acid? Al(s) + HCl(aq) AlCl3(aq) + H2(g)2 6 2 3

3.45 g ? grams

= g AlCl3

3.45 g Al

We must always convert to moles.

Almol 2

AlClmol 2 3

Now use the molar mass to convert to grams.

17.0

Mass to Mass Conversions

12

? L

Mass to Volume

75 g

1 mole of any gas occupies a volume of

22.4 L at STP

1 mole of any gas occupies a volume of

22.4 L at STP

75g C2H4

88 g C2O4

1mol C2O4 3 mol O2

1 mol C2O4 1mol O2

22.4 L O2

= 57.3 L O 2

Mole to mole ratio

Mole to mole ratio

Mole to volume

ratio

Mole to volume

ratio

Ethylene burns in oxygen to form carbon dioxide and water vapor. How many liters of water can be formed if 75 g of ethylene are consumed in this reaction?

C2H4(g) + 3 O2(g) 2 CO2(g) + 2 H2O(g)

13

? L

Another Mass to Volume

50 g

1 mole of any gas occupies a volume of 22.4 L at STP

1 mole of any gas occupies a volume of 22.4 L at STP

Calcium carbonate decomposes at high temperatures to form carbon dioxide and calcium oxide. If 50 g of CaCO2 decomposes. What volume of Carbon dioxide will be formed?

CaCO3(s) CO2(g) + CaO(s)

50 g CaCO3

100 g CaCO3

1mol CaCO3 1mol CO2

1mol CaCO3 1mol CO2

22.4 L CO2

= 11.2 L CO 2

Mole to mole ratio

Mole to mole ratio

Mole to volume

ratio

Mole to volume

ratio

14

? particles

Mole to Particle

10 moles 1 mole of any substance

contains 6.02 x 1023 particles1 mole of any substance

contains 6.02 x 1023 particles

= 3.0 x 1024particles of O2

Mole to mole ratio

Mole to mole ratio

Mole to particle

ratio

Mole to particle

ratio

10 mol H2

2 mol H2

1mol O2 6.02 x 1023 particles of O2

1 mol O2

Hydrogen gas reacts with oxygen gas to produce water. If 10 moles of H2 are given how many particles of O2 will react with the H2 gas?

2 H2(g) + O2(g) 2 H2O(g)

15

? particles

Another Mole to Particle

5moles 1 mole of any substance

contains 6.02 x 1023 particles1 mole of any substance

contains 6.02 x 1023 particles

=6 x 1024particles of H2O

Mole to mole ratio

Mole to mole ratio

Mole to particle

ratio

Mole to particle

ratio

5 mol O2

1 mol O2

2mol H2O 6.02 x 1023 particles of H2O

1 mol H2O

Hydrogen gas reacts with oxygen gas to produce water. If 5 moles of O2 are given how many particles of H2O will be produced ?

2 H2(g) + O2(g) 2 H2O(g)