Overview

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. This topic teaches students how to interpret chemical equations, balance them accurately, and use mole ratios to predict quantities of substances involved. These skills are foundational for problem solving in chemistry and critical for CLEP exam success.

Key Concepts and Structures

• Law of Conservation of Mass: Matter is neither created nor destroyed in a chemical reaction. This means equations must be balanced so the number of atoms of each element is the same on both sides.
• Balancing Chemical Equations: Adjust coefficients (not subscripts) to ensure equal atoms on both sides. Start with elements that appear in only one compound per side.
• Mole Ratios: Use the coefficients from a balanced equation to set up mole-to-mole conversion factors.
  2H₂ + O₂ → 2H₂O implies 2 moles of H₂ react with 1 mole of O₂ to produce 2 moles of H₂O.
• Molar Mass: The mass of one mole of a substance (in grams). Use it to convert between grams and moles.
• Mass–Mass Calculations: Convert grams → moles → use mole ratio → convert back to grams.
• Limiting Reactant: The reactant that runs out first and limits how much product can form. Identify by comparing mole ratios of available reactants.
• Theoretical Yield: The maximum amount of product expected based on the limiting reactant.
• Percent Yield: (actual yield ÷ theoretical yield) × 100%. Reflects efficiency of the reaction.
• Empirical vs. Molecular Formulas: The empirical formula shows the simplest whole-number ratio of atoms. The molecular formula shows the actual number of atoms in a molecule.

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