I. Stoichiometric Calculations

I. Stoichiometric

Calculations

Stoichiometry

A. Proportional Relationships

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

3/4 c. brown sugar

1 tsp vanilla extract

2 eggs

2 c. chocolate chips

Makes 5 dozen cookies.

2 1/4 c. flour

1 tsp. baking soda

1 tsp. salt

1 c. butter

3/4 c. sugar

5 eggs 5 doz.

2 eggs= 12.5 dozen cookies

Ratio of eggs to cookies

A. Proportional Relationships

Stoichiometry

• mass relationships between substances in a chemical reaction

• based on the mole ratio

Mole Ratio

• indicated by coefficients in a balanced equation

2 Mg + O2 2 MgO

B. Stoichiometry Steps

1. Write a balanced equation. Stoichiometry must start with a balance equation

2. Consider which of the following you are trying to do:

• moles moles (1 step)

• moles mass (2 steps)

• mass moles (2 steps)

• mass mass (3 steps)All of them must include moles moles

1 mol of a gas=22.4 Lat STP

C. Molar Volume at STP

Standard Temperature & Pressure0°C and 1 atm

How do I get to moles?

Molar Mass(g/mol)

6.02 1023

particles/mol

MASS

IN

GRAMS

MOLES

NUMBER

OF

PARTICLES

Molar Volume(22.4 L/mol)

LITERS

OF GAS

AT STP

Conversions including molarity

Molar Mass(g/mol)

6.02 1023

particles/mol

MASS

IN

GRAMS

MOLES

NUMBER

OF

PARTICLES

LITERS

OF

SOLUTION

Molar Volume(22.4 L/mol)

LITERS

OF GAS

AT STP

Molarity (mol/L)

Stoichiometry Problems: Moles to MolesIn a spacecraft, the carbon dioxide exhaled by astronauts can be removed by its reaction with lithium hydroxide, LiOH, according to the following chemical equation. How many moles of lithium hydroxide are required to react with 20 molCO2, the average amount exhaled by a person each day?

20 mol CO2 2 mol LiOH

1 mol CO2

= 40 mol

LiOH

? mol20 mol

CO2(g) + 2LiOH(s) → Li2CO3(s) + H2O(l)

Stoichiometry Problems: Moles to MassIn photosynthesis, plants use energy from the sun to produce glucose, C6H12O6, and oxygen from the reaction of carbon dioxide and water. What mass, in grams, of glucose is produced when 3.00 mol of water react with carbon dioxide?

3.00

molH2O1 mol C6H12O6

6 mol

H2O

= 90.1 g

C6H12O6

180.2 g C6H12O6

1 mol C6H12O6

3.00 mol ? g

6CO2(g)+6 H2O(l) → C6H12O6(s) + 6O2(g)

Stoichiometry Problems: Mass to MolesThe first step in the industrial manufacture of nitric acid is the catalytic oxidation of ammonia. If 824 g of NH3 is used in excess oxygen, how manly moles of NO are formed?

824 g NH31 mol

NH3

17.04 g

NH3

= 48.4 mol

NO

4 mol

NO

4 mol

NH3

824 g ? mol

4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)

Stoichiometry Problems: Mass to MassTin(II) fluoride, SnF2 is used in some toothpastes. It is made by the reaction of tin with hydrogen fluoride according to following equation. How many grams of SnF2 are produced from the reaction of 30.0 g HF with Sn?

30.0

g HF

1 mol

HF

20.01

g HF

= 117.5

g SnF2

Sn(s) + 2HF(g) SnF2(s) + H2(g)

1 mol

SnF2

2 mol

HF

156.7

g SnF2

1 mol

SnF2

30.0 g ? g

Stoichiometry Problems: Converting moles ↔ liters at STP

Add one of the following steps. Can be added to

the equation or done separately.

___ L 1 mol

22.4 L

= ___ mol22.4 L

1 mol

___ mol = ___ L

Stoichiometry Problems: Converting to/from liters at STP

In photosynthesis, plants use energy from the sun to produce glucose, C6H12O6, and oxygen from the reaction of carbon dioxide and water. How much, in liters, oxygen is produced when 3.00 mol of water react with carbon dioxide?

3.00 mol

H2O

6 mol

O2

6 mol

H2O

= 67.2 L O2

22.4 L

O2

1 mol

O2

3.00 mol ? L6CO2(g)+6 H2O(l) → C6H12O6(s) + 6O2(g)