4.3 Reaction Stoichiometry - Chemistry 2e | OpenStax

Learning Objectives

• Understand the concept of stoichiometry in chemical reactions.
• Use balanced chemical equations to derive stoichiometric factors relating reactants and products.
• Perform stoichiometric calculations involving mass, moles, and solution molarity.

Key Concepts

Role of Balanced Chemical Equations

• Provide identities of reactants and products.
• Coefficients indicate the relative number of molecules.
• Allows quantitative assessment of the relationships between substances in a reaction (stoichiometry).

Stoichiometric Relationships

• Similar to recipe proportions in cooking (e.g., pancake recipe analogy).
• Use coefficients in balanced equations to derive stoichiometric factors.
• Example: Production of ammonia from hydrogen and nitrogen.
  • Equation: [N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)]
  • Stoichiometric ratio: 2:3

Example Calculations

Example 4.8: Moles of Reactant Required

• Reaction: [2Al + 3I_2 \rightarrow 2AlI_3]
• Calculation: 0.429 mol Al requires 0.644 mol I2.

Example 4.9: Number of Product Molecules

• Reaction: [C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O]
• Calculation: 0.75 mol C3H8 produces 1.4 × 1024 CO2 molecules.

Example 4.10: Relating Masses of Reactants and Products

• Reaction: [MgCl_2(aq) + 2NaOH(aq) \rightarrow Mg(OH)_2(s) + 2NaCl(aq)]
• Calculation: 16 g Mg(OH)2 requires 22 g NaOH._

Example 4.11: Relating Masses of Reactants

• Reaction: [2C_8H_{18} + 25O_2 \rightarrow 16CO_2 + 18H_2O]
• Calculation: 702 g C8H18 requires 2.46 × 10^3 g O2._

Reaction Stoichiometry Calculations

• Involves using stoichiometric factors derived from balanced chemical equations.
• May involve computing various quantities, such as mass or molecules, depending on what is known and needed.
• Flowchart outlines typical steps for stoichiometry calculations.

Chemistry in Everyday Life: Airbags

• Airbags use chemical reactions for rapid inflation.
• Common reaction: Decomposition of sodium azide ([2NaN_3(s) \rightarrow 3N_2(g) + 2Na(s)]).
• Generates nitrogen gas to inflate the airbag quickly upon collision detection.
• Important engineering consideration: Correct amount of reactants for desired gas volume.

Note: Explore the OpenStax page for detailed examples and further reading.