Chapter 3 - Chemical Reactions and Reaction stoichiometry

• Why is it important to balance chemical equations?

  To ensure equal number of atoms on both sides
• What are coefficients in a balanced equation?

  Numbers that represent the amount of each substance
• What steps should be followed to balance a chemical equation?

  1. List reactants and products
  2. Count atoms of each element
  3. Balance each element from top to bottom
  4. Adjust coefficients as necessary
  5. Multiply by 2 if fractions are present
• What does stoichiometry deal with in chemical reactions?

  Numerical relationships between compounds
• How do you convert grams of a substance to moles?

  Use the formula: grams / molar mass
• What is the road map for stoichiometry calculations?

  Grams given → moles given → mole ratio → moles unknown → grams unknown
• What is a limiting reagent?

  Reactant completely consumed in a reaction
• What is theoretical yield?

  Maximum amount of product from a reaction
• What is percent yield?

  Actual yield / theoretical yield x 100
• What are the types of chemical reactions?

  • Combination: Two reactants form one product
  • Decomposition: One reactant breaks into multiple products
  • Combustion: Organic materials burn to produce CO₂ and H₂O
  • Displacement: More active element replaces a less active one
  • Neutralization: Acid and base react to form water
  • Redox: Changes in oxidation states occur
• What does the empirical formula represent?

  Relative number of atoms in simplest form
• How is the empirical formula calculated?

  From masses or percentages of elements
• What is the first step in determining the empirical formula from percentages?

  Convert percentages into grams assuming 100 g
• What should you do if you get a value of 0.1 or 0.9 when calculating the empirical formula?

  Round to the nearest whole number
• What does the molecular formula provide?

  Actual number of different elements in a compound
• What is the relationship between empirical and molecular formulas?

  Molecular formula is a multiple of empirical formula
• How can the empirical formula be calculated?

  From masses or percentages of elements
• What is the first step in determining the empirical formula from percentages?

  Convert percentages into grams
• Why is it important to avoid rounding errors in mole calculations?

  To ensure accurate whole number ratios
• What does the molecular formula represent?

  Actual number of elements in a compound
• What is the purpose of the n factor in molecular formulas?

  To relate empirical and molecular formulas
• How do you find the n factor for a molecular formula?

  Divide molar mass by empirical mass
• What is mass percent in a compound?

  Percent of a given element in a compound
• How is mass percent calculated?

  grams element / grams compound x 100
• What is the mass percent of carbon in sucrose?

  42.10%
• What is combustion analysis used for?

  To determine the empirical formula of a compound
• What are the products of combustion reactions involving carbon compounds?

  Carbon dioxide and water
• How do you convert grams of CO₂ to grams of carbon?

  Use the molar mass of CO₂
• What is the first step in combustion analysis for empirical formula determination?

  Convert grams of CO₂ to grams of C
• What is molar mass?

  Mass of a substance per mole
• What are the SI units for molar mass?

  g/mol
• How do you calculate the molar mass of (NH₄)₂SO₄?

  Add atomic masses of each element
• What is the relationship between moles and particles?

  One mole equals 6.022 x 10²³ particles
• What is Avogadro's number?

  6.022 x 10²³
• How do you convert molecules of Cl₂ to moles?

  Use Avogadro's number as a conversion factor
• How do you convert moles to grams for Cl₂?

  Multiply moles by molar mass
• How do you find grams from molecules of Cl₂?

  Convert molecules to moles, then to grams
• What are the steps to calculate the empirical formula?

  1. Write symbols for each element
  2. Convert percentages to grams
  3. Convert grams to moles
  4. Divide by the smallest mole value
  5. Round or multiply to get whole numbers
• What are the steps to calculate the molecular formula?

  1. Determine the empirical formula
  2. Calculate empirical mass
  3. Find n factor by dividing molar mass by empirical mass
  4. Multiply subscripts of empirical formula by n factor
• What are the steps in combustion analysis for empirical formula determination?

  1. Convert grams of CO₂ to grams of C
  2. Convert grams of H₂O to grams of H
  3. Subtract grams of C and H from the sample
  4. Convert all masses to moles
  5. Divide by the smallest mole value
  6. Round or multiply to get whole numbers