Reaction stoichiometry is all about the numbers behind chemical reactions. It helps us figure out how much stuff we need to make things happen in the lab and in real life. This is super useful for everything from cooking to rocket science!

We'll learn how to balance equations, calculate amounts of reactants and products, and solve problems involving mass and concentration. These skills are key for understanding how chemicals interact and for making precise measurements in chemistry experiments.

Reaction Stoichiometry

Stoichiometry in chemical reactions

• Quantitative study of reactants and products in a chemical reaction
  • Calculates quantities of substances consumed or produced (grams, liters, moles)
  • Helps determine limiting reactants and theoretical yields
• Based on the law of conservation of mass
  • Total mass of reactants equals total mass of products
  • Atoms are neither created nor destroyed, only rearranged
• Uses mole ratios derived from balanced chemical equations
  • Compares relative amounts of reactants and products
  • Coefficients in balanced equation represent mole ratios (H₂ + Cl₂ → 2 HCl)

Reactant and product quantity calculations

1. Start with a balanced chemical equation

   • Ensure equal number of atoms of each element on both sides (2 H₂ + O₂ → 2 H₂O)

2. Determine mole ratio between reactants and products

   • Use coefficients in balanced equation to establish mole ratio (2:1:2 for H₂:O₂:H₂O)

3. Convert given quantities (mass, volume, moles) of reactants or products to moles

   • Molar mass (g/mol) for solids and liquids (NaCl: 58.44 g/mol)
   • Molar volume (22.4 L/mol at STP) for gases (O₂: 22.4 L/mol at STP)

4. Use mole ratio to calculate moles of unknown reactant or product

   • Apply mole ratio from balanced equation (2 mol H₂ : 1 mol O₂)

5. Convert calculated moles back to desired unit (mass, volume, moles)

   • Molar mass for mass, molar volume for gases, molarity for solutions
   • Use dimensional analysis to ensure correct unit conversions

Mass, mole, and concentration problems

• For solutions, use concentration (molarity, M) to convert between volume and moles
  • Molarity (M) = moles of solute / liters of solution (0.5 M NaCl = 0.5 mol NaCl / 1 L solution)
  • Moles of solute = Molarity (M) × liters of solution (2.5 L of 0.5 M NaCl = 1.25 mol NaCl)
• When given mass of reactant or product, convert to moles using molar mass
  • Moles = mass (g) / molar mass (g/mol) (5 g NaCl / 58.44 g/mol = 0.0856 mol NaCl)
• Apply mole ratio from balanced chemical equation to determine moles of unknown substance
  • Use coefficients to set up proportion (2 mol H₂ : 1 mol O₂ = 4 mol H₂ : x mol O₂, solve for x)
• Convert calculated moles to desired unit (mass, volume, concentration)
  • Mass (g) = moles × molar mass (g/mol) (0.0856 mol NaCl × 58.44 g/mol = 5 g NaCl)
  • Volume (L) = moles × molar volume (22.4 L/mol at STP) for gases (1 mol O₂ × 22.4 L/mol = 22.4 L O₂ at STP)
  • Volume (L) of solution = moles of solute / molarity (M) (0.5 mol NaCl / 0.5 M = 1 L NaCl solution)

Additional Stoichiometric Concepts

• Percent yield: Compares actual yield to theoretical yield in a reaction
• Excess reactant: Reactant present in greater quantity than required by stoichiometry
• Empirical formula: Simplest whole-number ratio of atoms in a compound
• Stoichiometric point: When reactants are present in exact proportions according to balanced equation