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Chemistry 20

Chemistry 20. Unit D: Stoichiometry. Interpreting Chemical Reaction Equations. Chemical reaction equations show:  T he chemicals that react . T hese are called the reactants : which are located on the left-hand side of the reaction arrow T he chemicals that they produce .

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Chemistry 20

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  1. Chemistry 20 Unit D: Stoichiometry

  2. Interpreting Chemical Reaction Equations • Chemical reaction equations show: •  The chemicals that react. • These are called the reactants: which are located on the left-hand side of the reaction arrow • The chemicals that they produce. • These are called the products: which are located on the right-hand side of the reaction arrow

  3. Interpreting Chemical Reaction Equations 2 H2(g) + O2(g)2 H2O(g) ReactantsProducts Further the chemical reaction equations also show the states of chemicals

  4. Interpreting Chemical Reaction Equations However, chemical reaction equations do have some limitations. They do not describe the following:  Pressure and Temperature conditions • Many reactions do not happen at SATP

  5. Interpreting Chemical Reaction Equations However, chemical reaction equations do have some limitations. They do not describe the following: Progress and Process of a reaction • The equation only shows what is there at the beginning and the end it says nothing about what actually happened during the reaction

  6. Interpreting Chemical Reaction Equations However, chemical reaction equations do have some limitations. They do not describe the following: • Measurable Quantities of reactants in • any form that you can see directly • The reaction equation shows individual atoms/molecules/ions or moles, but we need to measure the mass or volume in the lab

  7. Interpreting Chemical Reaction Equations A reaction equation carries with it someassumptions: Reactions are spontaneous • The reaction will occur automatically when the reactants are mixed together • The reality is that this is not always the case. Example: Burning of wood • Corrosion of gold

  8. Interpreting Chemical Reaction Equations A reaction equation carries with it someassumptions: Reactions are fast • For the reaction to be useful it must occur in a reasonable time • The reality is that chemical rxn times vary. Example: Formation of rust • Aging of paper

  9. Interpreting Chemical Reaction Equations A reaction equation carries with it someassumptions: Reactions are quantitative • The reaction goes to completion; that is at least one of the reactants is essentially completely used up • The reality is that some chemical rxnstop well before all the reactants are used up

  10. Interpreting Chemical Reaction Equations A reaction equation carries with it someassumptions: Reactions are stoichiometric • There is a simple whole number ratio of reactants and products (these are indicated by the coefficients that you assigned)

  11. NET IONIC Equations Chemical Reaction Equations involving ionic compoundscan be written in one of three ways: Non-Ionic Reaction Equation Total Ionic Reaction Equation Net Ionic Reaction Equation

  12. NET IONIC Equations Non-Ionic Reaction Equation • In this type of reaction equation the elements and compounds that are involved in the reaction are written as elements, molecules or formula units • This is the type of reaction equations that you have been using since Junior High, Science 10, and the start of Chemistry 20

  13. NET IONIC Equations Non-Ionic Reaction Equation Examples: Cu(s) + 2AgNO3(aq) → 2Ag(s) + Cu(NO3)2(aq) 2NaNO3(aq) + BaCl2(aq) → 2NaCl(s) + Ba(NO3)2(aq)

  14. NET IONIC Equations Total Ionic Reaction Equation • In the Total Ionic Equation all the reactants that are involved are written as they would appear in an aqueous solution.

  15. NET IONIC Equations Total Ionic Reaction Equation • Recall, that ionic compounds undergo dissociation into their ions (cationsand anions) • Whereas, molecular compounds that dissolve, pure elements, precipitates, and gases are written as molecules. In other words they stay together when we write them out

  16. NET IONIC Equations Total Ionic Reaction Equation Example 1 Non-Ionic equation Cu(s) + 2AgNO3(aq) → 2Ag(s) + Cu(NO3)2(aq) Cu(s) + 2Ag+(aq)+ 2NO3–(aq)→ 2Ag(s)+ Cu2+(aq)+ 2NO3–(aq) Total Ionic equation

  17. NET IONIC Equations Total Ionic Reaction Equation Example 2 Non-Ionic equation 2AgNO3(aq)+ BaCl2(aq)→ 2AgCl(s)+ Ba(NO3)2(aq) 2Ag+ + 2NO3– + Ba2+ + 2Cl– → 2AgCl + Ba2+ + 2NO3– Total Ionic equation

  18. NET IONIC Equations Net Ionic Reaction Equation • In this type of equation only those entities that have “changed” are shown in the reaction equation • Changedmeans that there has been: • -a change of state for the entity • -a change of the overall charge for the • entity

  19. NET IONIC Equations Net Ionic Reaction Equation Those molecules and/or ions that do not“change” are not shown in the reaction. This means that they are exactly the same on both sides of the arrow. We will refer to these items as Spectators

  20. NET IONIC Equations Net Ionic Reaction Equation Spectatorsare those chemical entities that are present in a chemical reaction but do not actually take part in the reaction itself.

  21. NET IONIC Equations Net Ionic Reaction Equation Example 1 Total Ionic equation Cu(s) + 2Ag+(aq)+ 2NO3–(aq)→ 2Ag(s)+ Cu2+(aq)+ 2NO3–(aq) Cu(s) + 2Ag+(aq)→ 2Ag(s)+ Cu2+(aq) Net Ionic equation

  22. NET IONIC Equations Net Ionic Reaction Equation Example 2 Total Ionic equation 2Ag+ + 2NO3– + Ba2+ + 2Cl– → 2AgCl + Ba2+ + 2NO3– 2Ag+(aq) + 2Cl–(aq) → 2AgCl(s) Net Ionic equation

  23. Rules for Writing NET IONIC Equations Step 1: Write a balanced chemical equation (non-ionic reaction equation) Step 2: Write all the entities as they would appear in an aqueous solution. (remember the rules for this)

  24. Rules for Writing NET IONIC Equations Step 3: Cancel out any reactant–product pairs. (Those items on both sides of the arrow that are exactly the same) Step 4: Re-write the remaining entities (this will be the net ionic equation), reducing the coefficients if necessary

  25. Sample Problems for Writing NET IONIC Equations Pb(NO3)2(aq) + 2 NaI(aq) → PbI2(s) + 2NaNO3(aq) Pb2+(aq) + 2I–(aq) → PbI2(s) Pb(CH3COO)2(aq) + MgI2(aq)→PbI2(s) + Mg(CH3COO)2(aq) Pb2+(aq) + 2I–(aq) → PbI2(s)

  26. Sample Problems for Writing NET IONIC Equations BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq) Ba2+(aq) + SO42–(aq) → BaSO4(s) Zn(s) + CuSO4(aq) → Cu(s) + ZnSO4(aq) Zn(s) + Cu2+(aq) → Cu(s) + Zn2+(aq)

  27. Sample Problems for Writing NET IONIC Equations Ba(OH)2(aq) + 2 HCl(aq) → BaCl2(aq) + 2H2O(l) OH–(aq) + H+(aq) → H2O(l) Practice #10–14 on page 284 Section 7.1 #3–7 on page 285 Workbook pages 4–7

  28. Stoichiometry Stoichiometry • Is Greek for “measuring elements.” • It is the process of performing calculations of quantities in chemical reactions based on a balanced equation. • It allows us to calculate an unknown amount based on a known amount.

  29. Stoichiometry The most important part of this process is a correctly balanced chemical equation. From this one can calculate the amounts of reactants and products in terms of grams, moles, concentration, volumes, or particles.

  30. Stoichiometry The process of stoichiometry involves the following steps: • Obtain a correctly balanced equation • Determine the moles of your “given” substance:

  31. Stoichiometry The process of stoichiometry involves the following steps: • Determine the amount of moles of your required substance:

  32. Stoichiometry The process of stoichiometry involves the following steps: • Use the moles of required to calculate the appropriate amount requested:

  33. Stoichiometry Practice If 3.84 moles of acetylene ( C2H2(g)) are burned, how many moles of oxygen are used? g r  2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(g) ng= 3.84 mol nr=? &

  34. Stoichiometry Practice How many moles of methanol ( CH3OH(l)) are needed to burn in order to produce 8.96 moles of water vapor? r g  2CH3OH(l) + 3O2(g) → 2CO2(g) + 4H2O(g) nr=? ng= 8.96 mol

  35. Stoichiometry Practice Given the unbalanced formula below determine the moles of sulfuric acid required to react to produce 2.50 moles of aluminium sulfate? r g  3H2SO4(aq)+ 2Al(s) → 3H2(g) + Al2(SO4)3(s) nr=? ng= 2.50 mol &

  36. Gravimetric Stoichiometry Gravimetric stoichiometry is the process of calculating the masses of reactants or products in chemical reactions from knowing the mass of one entity involved in the reaction.

  37. Gravimetric Stoichiometry Gravimetric Stoichiometry involves the following steps: • Obtain a correctly balanced equation • Determine the moles of your “given” substance:

  38. Gravimetric Stoichiometry Gravimetric Stoichiometry involves the following steps: • Determine the amount of moles of your required substance:

  39. Gravimetric Stoichiometry Gravimetric Stoichiometry involves the following steps: • Use the moles of required to calculate the appropriate amount requested:

  40. Gravimetric Practice If you decompose 1.00 g of malachite Cu(OH)2CuCO3(s), what mass of copper (II) oxide would be formed? [The other products will be carbon dioxide and water vapor] g r Cu(OH)2CuCO3(s) → 2CuO(s) + CO2(g) + H2O(l) mg = 1.00 g mr = ? Mg = 221.13 g/molMr= 79.55 g/mol 

  41. Gravimetric Practice If you decompose 1.00 g of malachite Cu(OH)2CuCO3(s), what mass of copper (II) oxide would be formed? [The other products will be carbon dioxide and water vapor] g r Cu(OH)2CuCO3(s) → 2CuO(s) + CO2(g) + H2O(l) mg = 1.00 g mr = ? Mg = 221.13 g/molMr= 79.55 g/mol 

  42. Gravimetric Practice If you decompose 1.00 g of malachite Cu(OH)2CuCO3(s), what mass of copper (II) oxide would be formed? [The other products will be carbon dioxide and water vapor] g r Cu(OH)2CuCO3(s) → 2CuO(s) + CO2(g) + H2O(l) mg = 1.00 g mr = ? Mg = 221.13 g/molMr= 79.55 g/mol 

  43. Gravimetric Practice Iron is the most widely used metal in North America. It may be produced by the reaction of iron(III) oxide, from iron ore, with carbon monoxide to produce iron metal and carbon dioxide. What mass of iron(III) oxide is required to produce 100.0 g of iron? r g  Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g) mr= ? mg= 100.0 g Mr = 159.70 g/mol Mg= 55.85 g/mol 

  44. Gravimetric Practice Iron is the most widely used metal in North America. It may be produced by the reaction of iron(III) oxide, from iron ore, with carbon monoxide to produce iron metal and carbon dioxide. What mass of iron(III) oxide is required to produce 100.0 g of iron? r g Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g) mr= ? mg= 100.0 g Mr = 159.70 g/mol Mg= 55.85 g/mol 

  45. Gravimetric Practice Iron is the most widely used metal in North America. It may be produced by the reaction of iron(III) oxide, from iron ore, with carbon monoxide to produce iron metal and carbon dioxide. What mass of iron(III) oxide is required to produce 100.0 g of iron? r g Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g) mr= ? mg= 100.0 g Mr = 159.70 g/mol Mg= 55.85 g/mol 

  46. Gravimetric Practice If 2.50 g of aluminium foil reacted with copper(II) chloride, determine the mass of copper produced from the reaction. g r  2Al(s) + 3CuCl2(aq) → 3Cu(s) + 2AlCl3(aq) mg= 2.50 gmr= ? Mg = 26.98 g/molMr= 63.55 g/mol 

  47. Gravimetric Practice If 2.50 g of aluminium foil reacted with copper(II) chloride, determine the mass of copper produced from the reaction. g r 2Al(s) + 3CuCl2(aq) → 3Cu(s) + 2AlCl3(aq) mg= 2.50 gmr= ? Mg = 26.98 g/molMr= 63.55 g/mol 

  48. Gravimetric Practice If 2.50 g of aluminium foil reacted with copper(II) chloride, determine the mass of copper produced from the reaction. g r 2Al(s) + 3CuCl2(aq) → 3Cu(s) + 2AlCl3(aq) mg= 2.50 gmr= ? Mg = 26.98 g/molMr= 63.55 g/mol 

  49. Gravimetric Practice The exhaled carbon dioxide produced by astronauts can be removed from the air in the spacecraft using lithium hydroxide. The reaction produces lithium carbonate and water. Determine the mass of lithium hydroxide required to react completely with 1.00 kg of carbon dioxide. g r  CO2(g) + 2LiOH(s) → Li2CO3(s) + H2O(l) mg= 1000 gmr= ? Mg = 44.01 g/molMr= 23.95 g/mol 

  50. Gravimetric Practice The exhaled carbon dioxide produced by astronauts can be removed from the air in the spacecraft using lithium hydroxide. The reaction produces lithium carbonate and water. Determine the mass of lithium hydroxide required to react completely with 1.00 kg of carbon dioxide. g r CO2(g) + 2LiOH(s) → Li2CO3(s) + H2O(l) mg= 1000 gmr= ? Mg = 44.01 g/molMr= 23.95 g/mol 

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