Chapter 4: Stoichiometry

🧪 4.2 Classifying Chemical Reactions

Why Classify Reactions?

  • Helps predict products, energy changes, and reaction behavior.

  • Many reactions fall into recognizable patterns.

Main Types of Chemical Reactions

Combination (Synthesis) Reactions

  • Two or more substances combine to form one product.

  • General form:

    • A + B → AB

  • Example: formation of compounds from elements.

Decomposition Reactions

  • One compound breaks down into two or more simpler substances.

  • General form:

    • AB → A + B

  • Often require energy input (heat, light, electricity).

Single-Displacement (Replacement) Reactions

  • One element replaces another in a compound.

  • General form:

    • A + BC → AC + B

  • Occurs only if the replacing element is more reactive.

Double-Displacement (Metathesis) Reactions

  • Ions exchange partners between two compounds.

  • General form:

    • AB + CD → AD + CB

  • Often occurs in aqueous solutions.

Combustion Reactions

  • Substance reacts with oxygen, producing heat.

  • Hydrocarbon combustion produces CO₂ and H₂O.

⚖ 4.3 Reaction Stoichiometry

Stoichiometry

  • The quantitative relationship between reactants and products.

  • Based on balanced chemical equations.

Balanced Chemical Equations

  • Obey the law of conservation of mass.

  • Coefficients represent mole ratios.

Mole Ratios

  • Used to convert between amounts of substances.

  • Derived from coefficients in the balanced equation.

Steps in Stoichiometric Calculations

  1. Balance the equation.

  2. Convert given quantities to moles.

  3. Use mole ratios to find moles of desired substance.

  4. Convert moles to required units (grams, particles, etc.).

🎯 4.4 Reaction Yields

Theoretical Yield

  • Maximum amount of product predicted by stoichiometry.

  • Assumes the reaction goes to completion.

Actual Yield

  • Amount of product actually obtained in the lab.

Percent Yield

  • Measures efficiency of a reaction.

  • Formula:

    • (Actual Yield ÷ Theoretical Yield) × 100%

  • Percent yield is usually less than 100% due to:

    • Side reactions

    • Loss of product

    • Incomplete reactions

🔬 4.5 Quantitative Chemical Analysis

Gravimetric Analysis

  • Determines amount of substance by mass measurement.

  • Involves:

    • Precipitation of a solid

    • Filtering, drying, and weighing the precipitate

  • Used to determine concentration or purity.

  • Same way to solve with volumetric analysis.

Volumetric Analysis

  • Uses solution volume to determine amount of substance.

  • Most common method: titration.

Titration

  • A solution of known concentration reacts with an unknown solution.

  • Reaction continues until the equivalence point.

  • An indicator or instrument signals the endpoint.