stoichiometry calculating quantities needed in a chemical reaction 1

Stoichiometry

Calculating quantities needed in a chemical reaction

1

Importance of stoichiometryEssential Learning

• Manufacturing– Pharmaceuticals, plastics, detergents, cosmetics,

fibers and dyes, fertilizers, etc. – How much materials are needed to meet

customer orders? – How much starting material must be ordered or

made? • Research: Tracking a predicted reaction based

on the amount of product

2

3

Essential to Stoichiometry Set-up of problems

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

The mole ratio is the heart of the stoichiometry calculation

Important foundation knowledge for stoichiometry

• Mole Conversion

• Balancing chemical equations

• Writing correct formulas: – Word equations– Names & formulas

4

Essential to Stochiometry Mole conversions

5

Mole

Stoichiometry• Calculations to determine the __________ of

products produced or the ___________ of reactants needed in a chemical reaction.

(A) Stoichiometry calculations MUST have(1) (2)

6

B. Balanced equations are the ___________ for the chemical reactions.

C. Stoichiometry calculations always use only ________ substances in the reaction.

You assume that there is a sufficient amount of other substances to react.

7

Mole Ratio

8

Mole ratio: tells the correct proportions of substances for a chemical reaction.

Mole ratio: Starts with a balanced equation_ H₂SO₄+__ NaOH→__ Na₂SO₄+__ H₂0

H₂SO₄ NaOH Na₂SO₄ H₂0

Name

# molecules

# moles

9

Writing a Mole Ratio:

• Always use the _____________ of a ______________ equation.

• Always in a calculation, write: Mole:___________ Mole:

10

Writing the mole ratio: 1H₂SO₄+ 2NaOH→ 1Na₂SO₄+ 2H₂0

Given Mole Ratio Unknown

H₂SO₄ Na₂SO₄

H₂SO₄ H₂0

NaOH Na₂SO₄

NaOH H₂0

H₂0 H₂SO₄

Na₂SO₄ NaOH

11

Types of Stoichiometry Problems

• Mole• Mass • Volume • Combinations of above (mixed problems)

• Particles (compounds, molecules, atoms)Only sometimes

12

III. Mole to Mole Stoichiometry Problems

• Need ______________ equation • Need ______________ ratio

Given x

Mole Ratio = Unknown

Amount of given substance in moles

mole unknown mole given

= Amount of unknown substance in moles

13

X

Mole to Mole Calculations 1H₂SO₄+ 2NaOH→ 1Na₂SO₄+ 2H₂0

• How many moles of water will be produced if there are 10 moles of sodium hydoxide?

• How many moles of sulfuric acid are required if 135 moles of sodium sulfate must be produced?

14

Mole to Mole Calculations 1H₂SO₄+ 2NaOH→ 1Na₂SO₄+ 2H₂0

• How many moles of sodium hydroxide must be available to produce 17 moles of sodium sulfate?

15

Review: How many moles are in 120 grams of Sodium Sulfate?

• Formula for sodium sulfate

• Molar mass of sodium sulfate

• Mole conversion

16

Review: Mole to Mole Calculations

• How many moles of hydrochloric acid must be available to produce 20 moles of magnesium chloride?

17

Hydrochloric acid reacts with magnesiumto yield magnesium chloride and hydrogen

IV. Gram to Gram Calculations• Must use molar mass conversions

– Molar mass means: – Use the ____________ ____________

Given Conversion Mole Ratio Conversion Unknown

Mass of given substance(grams)

X 1 mole

Molar mass of given

X Mole

unknownMole

Given

XMolar mass of unknown

1 mole

= Mass of unknown substance

18

Gram to Gram Calculation 1H₂SO₄+ 2NaOH→ 1Na₂SO₄+ 2H₂0

• Must determine the molar mass (grams)

H₂SO₄ NaOH Na₂SO₄ H₂0

Molar mass(grams of 1 mole)

19

Gram to Gram Calculation 1H₂SO₄+ 2NaOH→ 1Na₂SO₄+ 2H₂0

• If 600 grams of sodium sulfate are required, how many grams of sodium hydroxide must be used?

20

Gram to Gram Calculation 1H₂SO₄+ 2NaOH→ 1Na₂SO₄+ 2H₂0

• If 325 grams of sodium sulfate are required, how many grams of sulfuric acid must be used?

21

Gram to Gram Calculation 1H₂SO₄+ 2NaOH→ 1Na₂SO₄+ 2H₂0

• If 540 grams of sodium hydroxide are available, how much sodium sulfate ( in grams) will be produced?

22

Gram to Gram Calculation 1H₂SO₄+ 2NaOH→ 1Na₂SO₄+ 2H₂0

• If 540 grams of sodium hydroxide are available, how many grams of sulfuric acid must be used?

23

Silent Lunch

• Why? Poor clean-up of the cafeteria– Expectation: You are responsible that all trash is

properly thrown away

• What: Silence– Walk down together to cafeteria in silence– Sit together in silence– All trash is thrown away and area is cleaned

• Failure to comply starts with ASD

24

Agenda – Dec. 3rd

• Warm-up: Stoichiometry preparation & practice

• Stoichiometry – Graphic organizer – Practice problems – individual, pair or team– Percent Yield

• Analysis of chemical reaction problems• Mole conversion practice

25

2 Li(OH)(s) + CO₂(g) → Li₂CO₃(s)+ H₂O(l)

Solid lithium hydroxide is used in the space shuttle to remove excess carbon dioxide from the living areas.

Show the problem set-up for each problem. Remember to label all quantities with units and formulas.

1. How many moles of lithium hydroxide are required to react with 15 moles of carbon dioxide?

2. If 200 grams of carbon dioxide must be removed each day, how many grams of lithium hydroxide are needed per day of the space voyage?

26

Skip slides for p4

• Skip slide 40 - 46

27

Mole to Gram Calculation2 Li(OH)(s) + CO₂(g) → Li₂CO₃(s)+ H₂O(l)

• If 10 moles of lithium hydroxide are available, how many grams of water will be produced?

28

Gram to Liter Calculation 2 Li(OH)(s) + CO₂(g) → Li₂CO₃(s)+ H₂O(l)

• If 100 grams of lithium hydroxide are available, how many liters of carbon dioxide must be used?

29

Help for Stoichiometry Problems

• Foldable • Graphic organizer

• Shows: – Mole ratio as heart (center) of all calculations– Given and Unknown – Mole conversions

30

Graphic organizer

31

Mole Ratio

Mole________Mole

Mole Mole

X

Foldable

32

Foldable

33

Foldable

34

Practice problemsTeacher led

PartnersAlternate problems with calculations

One student calculates the problem & then explains how she/he did it to the other student.

(Why? The process of explaining helps you in gaining and retaining the information.)

35

NO + O₂→ NO₂

36

NO O₂ NO₂

# moles

Molar mass

CS₂ + O₂→ CO₂ + SO₂

37

CS₂ O₂ CO₂ SO₂

# moles

Molar mass (g)

Review: Gram to Gram Calculation 1H₂SO₄+ 2NaOH→ 1Na₂SO₄+ 2H₂0

• If 540 grams of sodium hydroxide are available, how many grams of sulfuric acid must be used?

38

Percent Yield

• Stoichiometry calculations always give the maximum amount that can be produced.This is called the _________ ________.

• In real life, the maximum amount is never produced. Reactions do not proceed perfectly. The _________ ________

is produced.

39

Percent Yield

• Percent yield: Actual Yield x 100 = % Theoretical Yield

• In the last stoichiometry problem, 661.5 grams of sulfuric acid was calculated. However, the sample was weighed and found to

be 650.7 grams. The percent yield is: ______________ x 100 = %

Note: the % yield is always less than 100%

40

Analysis of Chemical Reaction problems

41

Putting all the steps together in a stoichiometry calculation

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

42

Putting all the steps together in a stoichiometry calculation

• Propane (C₃H₈) reacts with oxygen to produce carbon dioxide and water vapor.

• Balanced equation:

43

Example 1:

• How many moles of oxygen are required to completely react 10 moles of propane?

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

44

Example 1: • How many moles of oxygen are required to

completely react 10 moles of propane?

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

45

Example 2: • How many grams of oxygen are required to

completely react 10 moles of propane?

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

46

Molar mass of oxygen:

Example 3:

• How many liters of oxygen are required to completely react 10 moles of propane? Given:

Amount & Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

47

1 mole of oxygen at STP = ____________ liters

Magnesium reacts with hydrochloric acid to yield magnesium chloride and

hydrogen gas.

• Balanced equation:

48

Example 4: • How many moles of magnesium chloride will be produced if a

chemist starts with 120 grams of magnesium metal and plenty* of hydrochloric acid?

*Chemistry language: “with an excess of hydrochloric acid”

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

49

Molar mass of magnesium:

Example 5: • How many grams of magnesium chloride will be produced if a

chemist starts with 60 grams of magnesium metal and an excess of hydrochloric acid?

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

50

Molar mass of magnesium: Molar mass of magnesium chloride:

Example 6: • How many liters of Hydrogen gas will be produced

with 60 grams of hydrochloric acid and an excess of magnesium? Given:

Amount & Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

51

Molar mass of hydrochloric acid: 1 mole of hydrogen gas at STP:

Manufacturing Sulfuric Acid

Using stoichiometry in an industrial application

52

53

Here is a typical problem:• Sulfuric acid, an important chemical in

industry, is manufactured and sold by XYZ company.

• Sulfur dioxide gas is combined with water and oxygen to make H₂SO₄.

• The company is expecting a shipment of 500 kg of SO₂ and wants to know how much H₂SO₄ can be made from this shipment.

What are the steps to determine the amount of sulfuric acid?

1.

2.

3.

54

Determining sales value

• They can then calculate how much money they will make from the sale of their sulfuric acid.

• Water and oxygen are readily available and cheap, so the company uses an EXCESS of these substances, which means they use more than enough to react with the SO₂.

55

Sales

• If you can sell sulfuric acid for $10 per kg, how much will be the total sales ($)?

56