Unit 6 Section 3: Stoichiometry

• Analyze data and predict the stoichiometric ratios in a chemical equation

• Model the conservation of mass in a chemical equation

• Apply Math to interpret Chemical equations

Quantifying Reactants and Products

• Chemical equations work like a recipe

  • Balanced equations tell you the ingredients you need and the proper ratios

• Stoichiometry: The calculation of quantities in a chemical reaction​

  • Can be quantified in terms of moles, mass, volume, and number or atoms/molecules

    • The total amount of atoms remains the same throughout the equation due to the Law of Conservation of mass

  • Several types of Stoichiometry problems exist

    • Mole-Mole

    • Mole-Mass (Mole-Volume, Mole-Molecules)

    • Mass-Mass​

Proportionality of Reactants & Products

• In a chemical equation, the chemical symbols tell you the ingredients, and the coefficients in front of them tell you the ratios in terms of moles

  • Example: N_2(g) + 3H_{2 (g)} → 2NH_{3 (g)}

    • For every 1 mole of N_2, you can get 2 moles of NH₃

    • For every 3 moles of H₂ you can get 2 moles of NH₃

    • You need at least 1 mole of N₂ and 3 moles of H₂ for the reaction to take place

Mole Ratios

• A mole Ratio is a conversion factor derived from the coefficients of balanced equations​

  • Can be used to determine the amount of reactant or product involved in a chemical reaction​

    • ​Example: N_2(g) + 3H_{2 (g)} → 2NH_{3 (g)}

Mole-Mole Calculations

• Mole ratios are used in mole-mole calculations

  • Converting between the moles of one reactant/product and the moles of another reactant/product​

    • Given: The Moles of one part of the balanced equation

    • Want: The Moles of another part of the balanced equation

Mole-Mole Calculations Sample Problem #1

• How many moles of O₂ would you need to produce 25 moles of H₂O ?from the following equation: 2H₂ + O₂ →​ 2 H₂O

  • Step 1: Identify what value you are starting with

    • 25 moles H₂O

  • Step 2: identify the molar ratio for what you need

    • Going from H₂O to O₂

Mole-Mole Calculations Sample Problem #1

• How many moles of O₂ would you need to produce 25 moles of H₂O from the following equation: 2H₂ + O₂ →​ 2 H₂O ?

  • Step 1: Identify what value you are starting with

    • 25 moles H₂O

  • Step 2: identify the molar ratio for what you need

    • Going from H₂O to O₂

  • Step 3: Set up your conversion

Mole-Mole Calculations Sample Problem #2

• How many moles of ammonium (NH₃) are produced when 0.60 moles of nitrogen react with hydrogen in the Following Reaction: N₂ + 3H₂→​2NH₃

  • Step 1: Identify what you are starting with

    • 0.60 moles of Nitrogen

  • Step 2: Identify what ratio you need to get what you want​

Mole-Mole Calculations Sample Problem #2

• How many moles of ammonium (NH₃) are produced when 0.60 moles of nitrogen react with hydrogen?

  • Step 1: Write a balanced equation

    • N₂ + 3H₂→​2NH₃

  • Step 2: Identify what you are starting with

    • 0.60 moles of Nitrogen

  • Step 3: Identify what ratio you need to get what you want​

Mole-Mole Calculations Sample Problem #3

• Aluminum combines with oxygen gas to form Aluminum Oxide (Al₂O₃). How many moles of Aluminum are needed to form 3.7 mols of Aluminum Oxide?

  • Step 1: Write your balanced equation

    • ___Al + ___ O₂ →___Al₂O₃

Mole-Mole Calculations Sample Problem #3

• Aluminum combines with oxygen gas to form Aluminum Oxide (Al₂O₃). How many moles of Aluminum are needed to create 3.7 moles of Aluminum Oxide?

  • 4 Al + 3 O₂ →2 Al₂O₃

  • Step 2: Identify the molar ratio you need

Mole-Mole Calculations Sample Problem #3

• Aluminum combines with oxygen gas to form Aluminum Oxide (Al₂O₃). How many moles of Aluminum are needed to create 3.7 moles of Aluminum Oxide?

  • 4 Al + 3 O₂ →2 Al₂O₃

  • Step 2: Identify the molar ratio you need

  • Step 3: Set up your Conversion Factor

Mole-Mass Calculations

• You are given a quantity of a substance in Moles and asked to solve for the mass of an unknown quantity

  • To do this you need

    • the molar mass of a substance to convert from moles to grams​

    • a molar ratio between the two substances you are changing between

Mole-Mass Calculations Practice 1

• ​Potassium chlorate is sometimes decomposed in the laboratory to generate oxygen in the reaction: 2KClO₃(s) → 2KCl(s) + 3O₂(g). What mass of KClO₃ do you need to produce 0.50 mol O₂?

  • Step 1: Identify what you are starting with

    • 0.50 mol of O₂

  • Step 2: Identity what you need to know

    • Need:

      • Molar Ratio from the balanced equation

      • Mass of KClO₃

Mole-Mass Calculations Sample Problem 1

• ​Potassium chlorate is sometimes decomposed in the laboratory to generate oxygen in the reaction: 2KClO₃(s) → 2KCl(s) + 3O₂(g). What mass of KClO₃ do you need to produce 0.50 mol O₂?

  • Step 1: Identify what you are starting with

  • Step 2: Identify what you need to know

  • Step 3: Set up your conversion

Mole-Mass Calculations Practice 2

• ​Carbon, C(s), reacts with sulfur dioxide, SO₂(g), to form carbon disulfide, CS₂(l), and carbon dioxide, CO₂(g). How many grams of CO₂ would be produced if 0.852 mole of C is completely consumed by sulfur dioxide? 3 C + 2SO₂ → CS₂ + 2 CO₂

  • Step 1: Set up our equation with our molar ratio and molar mass conversions

Mole-Mass Calculations Practice 2

• ​Carbon, C(s), reacts with sulfur dioxide, SO₂(g), to form carbon disulfide, CS₂(l), and carbon dioxide, CO₂(g). How many grams of CO₂ would be produced if 0.852 mole of C is completely consumed by sulfur dioxide?

  • 3 C + 2SO₂ → CS₂ + 2 CO₂

  • Step 2: Set up our equation

Mole-Volume Calculations

• In a mole-to-volume problem, you are given a quantity of a substance in Moles and asked to solve for the volume of an unknown quantity for a gas

  • Only applies to gases at STP Conditions, when 1 mole of a gas = 22.4 Liters

Mole-Volume Sample Problem 1

• Nitrogen monoxide (NO), combines with Oxygen Gas to form the brown gas Nitrogen dioxide (NO₂) how many mol of NO₂ are produced when 34 L of O₂ reacts with an excess of NO at STP

  • ​Step 1: Write a balanced equation

    • __NO +__O₂ → __NO₂

Mole-Volume Sample Problem 1

• Nitrogen monoxide (NO), combines with Oxygen Gas to form the brown gas Nitrogen dioxide (NO₂) how many mol of NO₂ are produced when 34 L of O₂ reacts with an excess of NO at STP 2NO +__O₂ → 2NO₂

  • Step 1: Identify what you are starting with

    • Have to turn liters of O₂ into moles of NO₂ first

Mole-Volume Sample Problem 1

• Nitrogen monoxide (NO), combines with Oxygen Gas to form the brown gas Nitrogen dioxide (NO₂) how many liters of NO₂ are produced when 34 L of O₂ reacts with an excess of NO at STP?

  • ​Step 1: Write a balanced equation

  • Step 2: Set up your Conversion factors

Final Problem Type Grams to Grams

• You are given an amount for a reactant or product in grams, and you will turn it into grams of another reactant or product

  • Go from grams to moles, moles to moles, moles to grams

​ What mass of water is produced by burning 5.00 g of methane?Methane burns in air by the following reaction:

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

• ​Start with identifying what you have

  • 5 grams CH₄

• Identify a process

  • grams methane -> moles Methane ->moles water -> grams water

• Step one: find the mola​r masses for Methane and water andIdentify the Molar Ratio Needed

​

​

• Step 2: ​Set up the equation and Solve

   

​​ What mass of water is produced by burning 5.00 g of methane? Methane burns in air by the following reaction:

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

​​Grams to Grams Sample Problem 1

Grams to Grams Sample Problem 2

Oxygen gas can be produced by decomposing potassium chlorate using the reaction below. If 12.76 g of KClO₃ is heated and decomposes completely, what mass of oxygen gas is produced?

2KClO₃ (s)  →  2KCl (s) + 3O₂ (g)

​

• Step 1: Identify what we know and what we want

  • Know: 12.76 g of KClO₃

  • Want: grams of O₂

Grams to Grams Sample Problem 2

Oxygen gas can be produced by decomposing potassium chlorate using the reaction below. If 12.76 g of KClO₃ is heated and decomposes completely, what mass of oxygen gas is produced?

2KClO₃ (s)  →  2KCl (s) + 3O₂ (g)

Grams to Grams Sample Problem 2

Oxygen gas can be produced by decomposing potassium chlorate using the reaction below. If 12.76 g of KClO₃ is heated and decomposes completely, what mass of oxygen gas is produced?

2KClO₃ (s)  →  2KCl (s) + 3O₂ (g)

​

Grams to Grams Sample Problem 2

Oxygen gas can be produced by decomposing potassium chlorate using the reaction below. If 12.76 g of KClO₃ is heated and decomposes completely, what mass of oxygen gas is produced?

2KClO₃ (s)  →  2KCl (s) + 3O₂ (g)

Grams to Grams Sample Problem 3:

• Silver oxide, Ag₂O, reacts with hydrogen, H₂, at high temperatures to produce silver metal, Ag, and water, H₂O. The balanced equation is:

  • Ag₂O(s) + H₂(g) → 2 Ag(s) + H₂O(l)

• How many grams of Ag₂O must be consumed to produce 50.0 g of silver metal?

Grams to Grams Sample Problem 3:

• Silver oxide, Ag₂O, reacts with hydrogen, H₂, at high temperatures to produce silver metal, Ag, and water, H₂O. The balanced equation is:

  • Ag₂O(s) + H₂(g) → 2 Ag(s) + H₂O(l)

• How many grams of Ag₂O must be consumed to produce 50.0 g of silver metal?

Grams to Grams Sample Problem 3:

• Silver oxide, Ag₂O, reacts with hydrogen, H₂, at high temperatures to produce silver metal, Ag, and water, H₂O. The balanced equation is:

  • Ag₂O(s) + H₂(g) → 2 Ag(s) + H₂O(l)

• How many grams of Ag₂O must be consumed to produce 50.0 g of silver metal?

Grams to Grams Sample Problem 3:

• Silver oxide, Ag₂O, reacts with hydrogen, H₂, at high temperatures to produce silver metal, Ag, and water, H₂O. The balanced equation is:

  • Ag₂O(s) + H₂(g) → 2 Ag(s) + H₂O(l)

• How many grams of Ag₂O must be consumed to produce 50.0 g of silver metal?