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Stoichiometry

Stoichiometry. Stoy-kē-om’-etry. Main Concept. Stoichiometry is the measurement of elements Quantitative relationships between the compounds in a chemical reaction allow chemists to: Calculate the amount of reactant needed for a reaction Predict the quantity of the product

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Stoichiometry

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  1. Stoichiometry Stoy-kē-om’-etry

  2. Main Concept • Stoichiometry is the measurement of elements • Quantitative relationships between the compounds in a chemical reaction allow chemists to: • Calculate the amount of reactant needed for a reaction • Predict the quantity of the product • Determine formulas of the compounds • Simplify procedures in chemical analysis

  3. Two Types Composition Stoichiometry mass relationships of elements in compounds Reaction Stoichiometry mass relationships between reactants and products in a chemical reaction

  4. Reaction Stoichiometry • Classification • information given • information expected to find (unknown) • The information can either be both products, both reactants, or one of each. • Problems Solving • 4 methods • Ratios from balanced equation to convert the given quantities

  5. Methods • Given and Unknown in moles • No conversion necessary • Given (moles) and Unknown expressed in different mass (grams) • Solve for unknown, than convert the unknown substance in moles to grams • Given (grams) and Unknown (moles) • Convert given substance into moles, than solve for unknown • Given (grams) and Unknown (grams) • Convert given substance into moles • Find the unknown substance in moles • Convert the mass of the unknown substance into grams

  6. Mole Ratio • 2 mol AL2O3 : 4 mol AL • 2 mol AL2O3 : 3 mol O2 • 4 mol AL : 3 mol O2 • ANSWER: 26.0 mol Al • A conversion factor that relates the amount of moles of any two substance involved in chemical reaction. • Obtained through balanced chemical equation • EXAMPLE 1.a: 2AL2O3(l) -> 4Al (s) 3O2(g) Determine the amount in moles of aluminum that can be producced from 13.0 mol of aluminum oxide, the moles ration needed: Al to Al2O3

  7. Molar Mass Review: Molar mass is the conversion factor that relates the mass of a substance to the amount in moles of the substance Why Is It Important? Need to determine molar masses using the periodic table in order to solve reaction Stoichiometry problems

  8. Example 1.b: 1 mol Al2O3 = 101.96g 1 mol Al = 26.98 g 1 mol 02 = 32.00g From example 1.a we arrived at 26.0 mol Al Now find the number of grams of aluminum equivalent to 26.0 mol of aluminum

  9. Stoichiometric Calculations • Remember: • Balanced equation • Convert if necessary • Identify relationships • Answer the question fully • Example 2 • How many moles of lithium hydroxide are required to react with 20 mol CO2? • CO2(g) + 2LiOH(s) -> Li2CO3(s)+ H2O (l) Given: CO2 = 20 mol Unknown: amt. LiOH (mol)

  10. Example 3 • In photosynthesis, plants use energy from the sun to produce glucose, C6H12O6, and oxygen from the reaction of carbon dioxide and water. What mass, in grams, of glucose is produced when 3.00 mol of water react with carbon dioxide? • What is the given, what is the unknown? • What is the balanced equation? • What is the conversion factor? • Use periodic table?

  11. Limiting Reactants and Percentage Yield • Limiting Reactant: the reaction that limits the amount of the other reactant that can combine and the amount of product that can form in a chemical reaction • Excess reactant: the substance that is not used up completely in a reaction • C(s) + O2(g) -> CO2(g) • 1 mole carbon reacts with 1 mole oxygen forms on mole carbon dioxide • Could mix: 5 mol C with 10 mol O2 and reaction takes place. • However there is more oxygen than needed • What is the limiting reactant? • What is the reactant limiting?

  12. Example 1 Given: SiO2 + 4HF(g) -> SiF4(g) + 2H2O(l) If 6.0 mol hydrogen fluoride is added to 4.5 mol silicon dioxide What is the limiting agent?

  13. Percentage Yield • Theoretical yield • Maximum amt. of product that can be produced from a given amount of reactant • Actual yield • Measured amt. of a product obtained from a reaction • Percentage yield • Ratio of actual yield to theoretical yield mulitplied by 100

  14. Example 2 Chlorobenzene, C6H5Cl, is used in the production of many important chemicals, such as aspirin, dyes, and disinfectants. One industrial method of preparing chlorobenzene is to react benzene, C6H5, with chlorine, as represented below: C6H5(l) + Cl2(g) -> C6H5Cl(l) + HCL (g) When 36.8 C6H5 react with an excess of Cl2, the actual yield of C6H5Cl is 38.8 g. What is the percentage yield of C6H5Cl.

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