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Understanding Stoichiometry Conversions

Apr 29, 2025

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Introduction to Stoichiometry

Types of Stoichiometry Conversions

  1. Moles to Moles Conversion

    • Convert moles of substance A to moles of substance B using the mole ratio from a balanced chemical equation.
    • Example problem involves converting moles of sulfur dioxide (SO2) to moles of sulfur trioxide (SO3).

  2. Moles to Grams or Grams to Moles Conversion

    • Convert moles of substance A to grams of substance B or vice versa.
    • Use the molar ratio and the molar mass of the substances involved.

  3. Grams to Grams Conversion

    • Convert grams of substance A to grams of substance B.
    • This involves three steps: converting grams to moles, using the mole ratio, and then converting back to grams.

Example Problems

Problem 1: Sulfur Dioxide and Oxygen Reaction

  • Balanced Equation:
    • SO2 + O2 -> SO3
    • Balanced as 2 SO2 + O2 -> 2 SO3
  • Part A:
    • Given 3.4 moles of SO2, calculate moles of SO3.
    • Use mole ratio (2:2), resulting in 3.4 moles of SO3 formed.
  • Part B:
    • Given 4.7 moles of SO2, calculate moles of O2 needed.
    • Use mole ratio (2:1), resulting in 2.35 moles of O2.

Problem 2: Propane and Oxygen Reaction

  • Balanced Equation:
    • C3H8 + 5 O2 -> 3 CO2 + 4 H2O
  • Part A:
    • Given 2.8 moles of propane, calculate grams of CO2.
    • Steps: Convert moles of C3H8 to moles of CO2 using mole ratio (1:3), then convert to grams using molar mass of CO2 (44.01 g/mol).
    • Result is 369.5 grams of CO2.
  • Part B:
    • Given 3.8 moles of propane, calculate grams of O2 needed.
    • Steps: Use mole ratio (1:5) to find moles of O2, then convert to grams using molar mass of O2 (32 g/mol).
    • Result is 608 grams of O2.
  • Part C:
    • Given 25 grams of C3H8, calculate moles of water.
    • Steps: Convert grams to moles of C3H8 using its molar mass, use mole ratio (1:4) to find moles of H2O.
    • Result is 2.27 moles of H2O.
  • Part D:
    • Given 38 grams of H2O, calculate moles of CO2.
    • Steps: Convert grams to moles using molar mass of H2O (18.016 g/mol), use mole ratio (3:4) to find moles of CO2.
    • Result is 1.58 moles of CO2.

Problem 3: Aluminum and Chlorine Reaction

  • Balanced Equation:
    • 2 Al + 3 Cl2 -> 2 AlCl3
  • Part A:
    • Given 35 grams of aluminum, calculate grams of AlCl3.
    • Steps: Convert grams to moles of Al, use mole ratio to find moles of AlCl3, then convert to grams using molar mass (133.33 g/mol).
    • Result is 172.96 grams of AlCl3.
  • Part B:
    • Given 42.8 grams of aluminum, calculate grams of chlorine.
    • Steps: Convert grams to moles of Al, use mole ratio to find moles of Cl2, then convert to grams using molar mass of Cl2 (70.9 g/mol).
    • Result is 168.75 grams of Cl2.

Key Concepts

  • Mole Ratio: Essential for converting between different substances in a chemical reaction.
  • Molar Mass: Used to convert between grams and moles.
  • Balanced Chemical Equations: Necessary for determining mole ratios.

These problems illustrate common types of stoichiometry calculations you may encounter in chemistry classes.

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