General Chemistry I Week 6 Notes

Week 6 Agenda

• Sections Covered:

  • 4.1 Writing and Balancing Chemical Equations

  • 4.2 Classifying Chemical Reactions

  • 4.3 Reaction Stoichiometry

  • 4.4 Reaction Yields

  • 4.5 Quantitative Chemical Analysis

Section 4.1: Writing and Balancing Chemical Equations

Learning Objectives

• Derive chemical equations from narrative descriptions.

• Write and balance equations in molecular, total ionic, and net ionic formats.

Chemical Equations Basics

• A balanced chemical equation represents identities and quantities of substances in a reaction.

Elements of a Chemical Equation:

1. Reactants (left side)

2. Products (right side)

3. Plus signs (+) separate reactants and products.

4. An arrow (⟶) shows the direction of the reaction.

5. Coefficients indicate the number of molecules (1 is usually omitted).

Example of a Chemical Reaction

• Reaction of methane (CH₄) and oxygen:

  • Equation: CH₄ + 2 O₂ ⟶ CO₂ + 2 H₂O

Balancing Chemical Equations

• Balanced equations have equal atom counts for each element.

• Use coefficients to achieve balance, starting from the most complex molecule.

Section 4.2: Classifying Chemical Reactions

Learning Objectives

• Define and identify three common reaction types:

  • Precipitation

  • Acid-base

  • Oxidation-reduction

Precipitation Reactions

• Reactants in solution form solid products.

• Example:

  • Molecular Equation: 2 KI(aq) + Pb(NO₃)₂(aq) ⟶ PbI₂(s) + 2 KNO₃(aq)

  • Net Ionic Equation: Pb²⁺(aq) + 2 I⁻(aq) ⟶ PbI₂(s)

Section 4.3: Reaction Stoichiometry

Learning Objectives

• Understand stoichiometry in chemical reactions.

• Calculate amounts of reactants and products using stoichiometric factors.

Stoichiometric Relationships

• Balanced chemical equations offer ratios for transforming masses and moles of reactants/products.

• Example Problem: How many moles of I₂ needed for 0.429 moles of Al?

  • Calculation: 0.429 moles Al x (3 moles I₂ / 2 moles Al) = 0.644 moles I₂

Section 4.4: Reaction Yields

Learning Objectives

• Understand theoretical yield and limiting reactants.

• Calculate percent yield.

Yield Concepts

• Theoretical Yield: Maximum product amount expected from a reaction according to stoichiometry.

• Limiting Reactant: Reactant that runs out first, limiting product formation.

  • Example: In H₂ + Cl₂ ⟶ 2HCl, if 3 moles H₂ and 2 moles Cl₂ are used, Cl₂ is limiting.

• Percent Yield: Calculated as:

  • % Yield = (Actual Yield / Theoretical Yield) x 100

Section 4.5: Quantitative Chemical Analysis

Learning Objectives

• Perform stoichiometric calculations using titration and gravimetric analysis data.

Titration

• Involves measuring volumes for determining concentrations.

• Indicators are used to signal concentration equivalence.

• Example Problem in Titration: Finding molarity of HCl from NaOH titrant used.

Gravimetric Analysis

• Involves precipitation reactions to isolate analytes.

• Example: Analyzing a 0.4550 g mixture containing MgSO₄ via precipitation with Ba(NO₃)₂, yielding BaSO₄.

Key Techniques:

• Combustion Analysis: Determines elemental composition of hydrocarbons through combustion to CO₂ and H₂O.

  • Stoichiometric calculations from collected gases yield empirical formulas.