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Mastering Stoichiometry: Quantitative Relationships in Chemistry

Dive into the world of stoichiometry and explore the mass and quantity relationships among reactants and products in chemical reactions. Learn how to convert between moles, particles, mass, and volume using coefficients in balanced chemical equations.

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Mastering Stoichiometry: Quantitative Relationships in Chemistry

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  1. Stoichiometry A Study of Quantitative Relationships

  2. Stoichiometry is: • Mass and quantity relationships among reactants and products in a chemical reaction • Involves conversions to moles, particles, mass and volume of chemical formulas

  3. Coefficients: • Represent the number of particles involved in a chemical reaction • Represent the relative moles of reactants and products in a reaction • All coefficients in a balanced chemical equation are related

  4. Mole to Mole Problems • It is possible to convert from moles of one substance to moles of another using information found in balanced chemical equation Example: 2H2 (g) + O2 (g) 2H2O(l) This equation shows that 2 moles of H2 will react with 1 mole of O2 to form 2 moles of H2O

  5. To perform the conversions: • Write a balanced chemical equation • Take the number of moles of one substance and convert to number of moles of another substance using dimensional analysis

  6. # mol A x # mol B from equation= # mol B # mol A from equation Example: How many moles of water are formed when 3.0 moles of hydrogen gas is burned? 2 H2(g) + O2(g) 2 H2O(l) 3.0 mol H2 x 2 mol H2O = 3.0 mol H2O 2 mol H2

  7. Another Example: Moles to Moles 2 Fe(s) + 3 Cl2 (g) 2 FeCl3 (s) How many mol of FeCl3 will form if 6 mol of Cl2 reacts with excess iron? 6 mol Cl2 x 2 mol FeCl3 = 4 mol FeCl3 3 mol Cl2 Called “mole ratio”

  8. Sample Problem – Moles to Moles Aluminum hydroxide reacts with hydrochloric acid according to the equation: Al(OH)3 + 3HCl AlCl3 + 3H2O How many moles of acid will react with 0.200 mol of Al(OH)3? a. c. b. d.

  9. Solving Stoichiometric Problems • There are three main categories; all follow the same basic logic: • Mass – mass problems • Mass – volume problems • Volume – volume problems

  10. Mass – Mass Problems • Given the mass of one substance, find the mass of another substance in the same reaction • Solve using three steps: • Convert mass given to moles using molar mass • Find molar ratio using coefficients from the balanced equation to convert moles of given to moles of unknown • Convert to mass of unknown using molar mass of unknown

  11. Steps for mass to mass conversions Grams of Known Moles of Known Moles of Unknown Grams of Unknown Mole Ratio Molar Mass of Unknown Molar Mass Of Known This chart shows the steps to convert from known mass to unknown mass

  12. Sample Problem – Mass to Mass What mass of water is produced from the decomposition of 25.0 g of ammonium nitrate? NH4NO3 (s) N2O(g) + 2 H2O(l)

  13. Sample Problem – Mass to Mass Determine the mass of N2 produced if 100.0 g NaN3 (sodium azide) is decomposed. 2NaN3(s) 2Na(s) + 3N2 (g)

  14. Sample Problem - Mass to Mass If 2.50 g of SO2 react with excess oxygen and water, how many grams of H2SO4 are produced? 2SO2(g) + O2(g) + 2H2O(l) 2H2SO4(l) a. c. b. d.

  15. To solve mass – volume problems • Convert the mass given to moles using molar mass • Find the molar ratio using coefficients from the balanced chemical equation to convert the moles of the given substance to moles of the unknown substance • Convert to volume of unknown using molar volume of unknown

  16. Sample Problem – Mass to Volume • Ammonia is synthesized from hydrogen and nitrogen gases: N2(g) + 3H2(g) 2NH3(g) Problem: If 5.00 L of nitrogen reacts completely, how many grams of ammonia are produced at STP?

  17. Another Sample Problem Use the reaction to calculate the mass of solid ammonium nitrate that must be used to obtain 0.100 L of dinitrogen monoxide gas at STP. NH4NO3(s) N2O(g) + 2H2O(l)

  18. Sample Problem - Mass to Volume How many liters of carbon dioxide will be produced at STP if 2.38 kg of calcium carbonate reacts completely? CaCO3(s) CaO(s) + CO2(g) a. c. b. d.

  19. To solve volume-volume problems: • Convert the volume given to the volume of unknown by using coefficients in the balanced chemical equation as a ratio of liters instead of moles

  20. Sample Problem What volume of oxygen gas is needed for the complete combustion of 4.00 L of propane gas (C3H8) at STP? Step 1: Write Balanced Chemical Equation C3H8(g) + 5O2(g) 3CO2(g)+ 4H2O(g) Step 2: Begin Dimensional analysis by converting 4.00 L of propane to oxygen using “volume ratio” ?L O2 = 4.00 L C3H8 x 5 L O2 = 20 L O2 1 L C3H8

  21. Sample Problem – Volume to Volume What volume of oxygen is needed to react with solid sulfur to form 3.5 L SO2 at STP?

  22. Sample Problem – Volume to Volume Determine the volume of hydrogen gas needed to react completely with 5.00 L of oxygen gas to form water at STP. a. c. b. d.

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