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Stoichiometry

Stoichiometry. Chemistry Chapter 12 Lesson 1. Stoichiometry. Stoichiometry is the study of the quantitative relationships between amounts of reactants used and products formed by a chemical reaction.

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Stoichiometry

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  1. Stoichiometry Chemistry Chapter 12 Lesson 1

  2. Stoichiometry • Stoichiometry is the study of the quantitative relationships between amounts of reactants used and products formed by a chemical reaction. • Because of the Law of Conservation of Mass, it is known that the mass at the beginning of a reaction will equal the mass at the end of the reaction. • The mass of the products MUST equal the mass of the reactants.

  3. Steps in Stoichiometric Calculations Write a balanced chemical equation and interpret the equation in terms of moles. Determine the moles of the given substance using a mass-to-mole conversion. Determine the moles of the unknown substance from the moles of the given substance. From the moles of the unknown substance, determine the mass of the unknown using a mole-to-mass conversion.

  4. Mole Ratios • A mole ratio is a ratio between the number of moles of any two substances in a balanced chemical equation. • The number of possible mole ratios is equal to the number of parts in the equation multiplied to the next smallest number. • Three parts in the following equation, so 6 (3x2) possible molar ratios • 2 KClO3 (s)  2 KCl (s) + 3 O2 (g)

  5. Stoichiometry Calculations • Mole to mole conversions: • Start by writing the balanced chemical equation. • Identify the substance that you know and the substance that you need to determine. • Use the mole ratio from the balanced equation to determine the number of moles of the unknown.

  6. Example Problem • How many moles of CO2 are produced when 10.0 moles of propane (C3H8) are burned in excess oxygen? • C3H8 (g) + 5 O2 (g)  3 CO2 (g) + 4 H2O (l) • 10 mol C3H8 and ? Moles CO2 • Mole ratio 1 C3H8to 3 CO2 • 10 mol C3H8 x3 mol CO2/1 mol C3H8 = 30 mol CO2

  7. Practice Problem A reaction between methane and sulfur produces carbon disulfide (CS2), a liquid often used in the production of cellophane. _____ CH4 (g) + ____ S8 (s)  ____CS2 (l) + ____ H2S(g) Balance the equation. Calculate the mol CS2 produced when 1.5 mol S8is used. How many mol H2S is produced?

  8. Conversions • Mole-to-Mass Conversion • Convert from mass to moles then use the technique for a mole-to-mole conversion. • Mass-to-Mass Conversion • Convert from mass to moles for the reactants and products. • Then use the technique for a mole-to-mole conversion. • Then convert back from moles to mass for the reactants and products.

  9. Example Problem Determine the mass of sodium chloride (NaCl) produced when 1.25 mol of chlorine gas (Cl2) reacts with sodium. _____ Na (s) + ____ Cl2 (g)  ____ NaCl (s)

  10. Practice Problem One in a series of reactions that inflate air bags in automobiles is the decomposition of sodium azide (NaN3). 2 NaN3(s)  2 Na(s) + 3 N2 (g) Determine the mass of N2produced if 100.0 grams of NaN3 decomposes.

  11. Homework Do problems 61-64, 66-74 even on pages 379 and 380. They are due tomorrow.

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