OPX_AtomsFirst2e_Chapter7 (2)

Chapter 7: Stoichiometry of Chemical Reactions

7.1 Writing and Balancing Chemical Equations

• Chemical equations represent chemical reactions with symbols.

• Reactants are on the left, products on the right.

• Coefficients show relative amounts; must be balanced for all elements.

• Shortcuts: Use fractions for intermediate balancing; convert to whole numbers at the end.

• Example: CH4 + 2O2 ⟶ CO2 + 2H2O is balanced.

7.2 Classifying Chemical Reactions

• Types of Reactions:

  • Precipitation: Forms solid from solutions (e.g., double displacement).

  • Acid-Base: Transfer of H+ ions (e.g., HCl + NaOH → NaCl + H2O).

  • Oxidation-Reduction (Redox): Change in oxidation states.

• Identify based on descriptions and equations.

7.3 Reaction Stoichiometry

• Stoichiometry relates amounts of reactants and products based on balanced equations.

• Use coefficients to derive stoichiometric factors for calculations.

• Example: 2 Al + 3 I2 ⟶ 2 AlI3 shows a ratio of 2 mol Al to 3 mol I2.

7.4 Reaction Yields

• Theoretical Yield: Amount of product predicted by stoichiometry.

• Actual Yield: Amount collected during a reaction; usually less than the theoretical yield.

• Percent Yield: (Actual Yield / Theoretical Yield) × 100.

• Example: If 0.5072 g Cu is theoretical but only 0.392 g is obtained, percent yield = 77.3%.

7.5 Quantitative Chemical Analysis

• Titration: Method to determine concentration of analyte using a titrant of known concentration.

• Indicators change color at equivalence point, marking the endpoint.

• Calculations are based on the reaction stoichiometry from titration data.