Chapter 9 Section 1 Stoichiometry Answers

Chapter 9 Section 1 Stoichiometry Answers Chapter 9 Section 1 Stoichiometry Answers I Stoichiometry The branch of chemistry that involves the study of the quantitative relationships between reactants and products in chemical reactions Key Concepts Mole The SI unit for amount of substance Molar Mass The mass of one mole of a substance Avogadros Number The number of particles atoms molecules ions in one mole of a substance 6022 x 1023 Chemical Equation A symbolic representation of a chemical reaction Balancing Chemical Equations Ensuring the number of atoms of each element is equal on both sides of the equation II Stoichiometric Calculations Calculating Mole Ratios The coefficients in a balanced chemical equation represent the mole ratios of reactants and products Calculating Grams to Moles and Moles to Grams Grams to Moles Divide the mass of a substance by its molar mass Moles to Grams Multiply the number of moles by the molar mass of the substance Calculating Moles to Particles and Particles to Moles Moles to Particles Multiply the number of moles by Avogadros number Particles to Moles Divide the number of particles by Avogadros number III Practice Problems Problem 1 Question How many moles of sodium chloride NaCl are produced when 25 moles of sodium Na react completely with excess chlorine gas Cl2 Balanced Chemical Equation 2Na Cl2 2NaCl Solution 1 Identify the mole ratio From the balanced equation 2 moles of Na react to produce 2 2 moles of NaCl 2 Set up a proportion 2 mol NaCl 2 mol Na x mol NaCl 25 mol Na 3 Solve for x x 25 mol NaCl Answer 25 moles of sodium chloride are produced Problem 2 Question What is the mass of carbon dioxide CO2 produced when 100 grams of methane CH4 is burned completely in oxygen Balanced Chemical Equation CH4 2O2 CO2 2H2O Solution 1 Convert grams of CH4 to moles 100 g CH4 1604 gmol CH4 0624 mol CH4 2 Identify the mole ratio From the balanced equation 1 mole of CH4 produces 1 mole of CO2 3 Convert moles of CO2 to grams 0624 mol CO2 4401 gmol CO2 274 g CO2 Answer 274 grams of carbon dioxide are produced Problem 3 Question How many molecules of water H2O are produced when 025 moles of hydrogen gas H2 react with excess oxygen Balanced Chemical Equation 2H2 O2 2H2O Solution 1 Identify the mole ratio From the balanced equation 2 moles of H2 produce 2 moles of H2O 2 Convert moles of H2O to molecules 025 mol H2O 6022 x 1023 moleculesmol 151 x 1023 molecules of H2O Answer 151 x 1023 molecules of water are produced IV Applications of Stoichiometry Predicting the Amount of Products Stoichiometry allows chemists to predict the amount of products that can be formed from a given amount of reactants Determining Limiting Reactants The limiting reactant is the reactant that is completely consumed in a chemical reaction thereby limiting the amount of product formed Calculating Percent Yield The percent yield is the ratio of the actual yield the amount of 3 product obtained to the theoretical yield the amount of product predicted by stoichiometry V Conclusion Stoichiometry is a fundamental concept in chemistry that enables us to understand the quantitative relationships between reactants and products in chemical reactions By mastering the principles of stoichiometry we can accurately predict the amount of product that can be formed from a given amount of reactants identify the limiting reactant and calculate the percent yield of a reaction