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Unit 5: The Mole and Stoichiometry

Unit 5: The Mole and Stoichiometry. What Can A Coefficient Equal?. A coefficient represents the number of elements or molecules in a chemical equation. It is different from a subscript which measures the number of atoms or polyatomic ions within a molecule. 2 CO + O 2  2 CO 2

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Unit 5: The Mole and Stoichiometry

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  1. Unit 5: The Mole and Stoichiometry

  2. What Can A Coefficient Equal? • A coefficient represents the number of elements or molecules in a chemical equation. It is different from a subscript which measures the number of atoms or polyatomic ions within a molecule. • 2 CO + O 2 2 CO 2 C oefficients S ubscripts • Come after an element or polyatomic ion • Come in front of an element or molecule • Big numbers • Small numbers • Means that every element or molecule in a compound get multiplied by it. • Only tell how many of an element there are within a compound

  3. A Coefficient can represent two different things: 1. Number of molecules of a reactant or product in an equation. 2. Number of moles of a reactant or product in an equation. • In either case, the coefficients give the ratio between the numbers in a chemical reaction (this is why balancing is important)! • 2CO(g) + 1O2(g)  2CO2 • The reactant ratio is 2:1

  4. Using the Mole • Coefficients in balanced chemical equations represent MOLES or Molecules • Zn + 2 HCl  ZnCl2 + H2 1 mole (or atom) of Zn reacts with 2 moles (or molecules) of hydrochloric acid to produce 1 mole(or molecule) of zinc chloride and 1 mole(or molecule) of hydrogen gas.

  5. Back to the reaction • Zn + 2 HCl  ZnCl2 + H2 • To carry out this reaction, how much zinc and HCl will be needed to make the reaction go to completion? • 1 mole of Zn and 2 moles of HCl • How many moles of HCl will be needed if I have 2 moles of zinc? 4 moles of HCl

  6. How many moles of Copper (I) Sulfide could be produced from 6 moles of Copper (I) Chloride reacting with an excess of H2S gas? 1. Write a balanced equation. Determine what you start with and what you want to know. H2S + CuCl  Cu2S + HCl 2 2

  7. H2S + 2CuCl  Cu2S + 2HCl 2. Covert moles of what you start with to moles of what you want to know using a mole ratio. • *A mole ratio compares two products or reactants using the coefficients of the balanced equation • (in this case 2 moles CuCl:1 mole Cu2S). 6 moles CuCl 1 mole Cu2S = 3 moles Cu2S 2 moles CuCl

  8. H2S + 2CuCl  Cu2S + 2HCl • How many moles of HCl would be produced starting with the same amount? 6 moles CuCl 2 moles HCl 2 moles CuCl = 6 moles HCl

  9. 3 2 3 Al + H2CO3 Al2(CO3) 3 + H2 • Suppose Carlos gets 10 moles of Aluminum for his birthday. How much of each product can he make? 10 moles Al 1 mole Al2(CO3)3 = 5 moles Al2(CO3)3 2 moles Al 10 moles Al 3 moles H2 = 15 moles H2 2 moles Al

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