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Section 2: Stoichiometric Calculations

Section 2: Stoichiometric Calculations. Stoichiometry. Learning Goals. List the sequence of steps used in solving stoichiometric problems . Solve stoichiometric problems. Using Stoichiometry. All stoichiometric calculations begin with a balanced chemical equation.

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Section 2: Stoichiometric Calculations

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  1. Section 2: Stoichiometric Calculations Stoichiometry

  2. Learning Goals • List the sequence of steps used in solving stoichiometric problems. • Solve stoichiometric problems.

  3. Using Stoichiometry • All stoichiometric calculations begin with a balanced chemical equation. 4Fe(s) + 3O2(g)  2Fe2O3(s)

  4. Using Stoichiometry • Steps to solve mole-to-mole, mole-to-mass, and mass-to-mass stoichiometric problems: • Write a balanced chemical equation for the reaction. • Determine where to start your calculations by noting the unit of the given substance.

  5. Using Stoichiometry • If mass (in grams) of the given substance is the starting unit, you must convert to moles. • If amount (in moles) of the given substance is the starting unit, convert moles of the given substance to moles of the unknown.

  6. Using Stoichiometry • The end point of the calculation depends on the desired unit of the unknown substance. • If the answer must be in moles, stop you are finished. • If the answer must be in grams, convert moles of unknown to grams of unknown using the molar mass as the conversion factor.

  7. Example • The carbon dioxide exhaled by astronauts can be removed from a spacecraft by reacting with lithium hydroxide as follows: CO2(g) + LiOH(s)→ Li2CO3(s) An average person exhales about 20 moles of CO2 per day. How many moles of LiOH would be required to maintain 2 astronauts in a spacecraft for three days?

  8. Example • Balance equation: CO2 + LiOH→ Li2CO3+ H2O • Determine moles of given substance: 20 moles per person, 2 people = x 3 days = moles of CO2

  9. Example • Convert moles of given substance to moles of unknown: CO2  LiOH

  10. Practice • How many moles of carbon dioxide are produced when 10.0 mol of propane (C3H8) are burned in excess oxygen in a gas grill?

  11. Practice • Methane and solid sulfur (S8) react to produce carbon disulfide, a liquid used in the production of cellophane. Hydrogen sulfide gas is also produced. • Write the chemical equation. • Calculate the moles of CS2 produced when 1.50 mol of S8 are used. • How many moles of H2S are produced?

  12. Practice • Determine the mass of sodium chloride produced when 1.25 mol of chlorine gas reacts vigorously with excess sodium.

  13. Practice • Ammonium nitrate, an important fertilizer, produces dinitrogen monoxide gas and water when it decomposes. Determine the mass of water produced from the decomposition of 25.0 g of solid ammonium nitrate.

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