Molar Ratios

• 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

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)}

Types of Stoichiometry Problems

• Several types of Stoichiometry problems

  • Mole-Mole

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

  • Mass-Mass​

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?

  • Step 1: Write a balanced equation

    • __N₂ + __H₂→​__NH₃

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 #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