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Chapter 9 - PowerPoint PPT Presentation


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Quantities in Chemical Reactions. Chapter 9. Stoichiometry. Calculations involving chemical equations Chemical equations tell us exactly how much of one reactant will react (combine) with a second reactant and how much of the product we should expect. 2 Al + 6 HCl  2 AlCl 3 + 3 H 2.

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stoichiometry
Stoichiometry
  • Calculations involving chemical equations
  • Chemical equations tell us exactly how much of one reactant will react (combine) with a second reactant and how much of the product we should expect.
2 al 6 hcl 2 alcl 3 3 h 2
2 Al + 6 HCl  2 AlCl3 + 3 H2
  • 2 atom Al + 6 molecule HCl  2 formula unit AlCl3 + 3 molecule H2
  • 2 mol Al + 6 mol HCl  2 mol AlCl3 +3 mol H2
  • 2 (26.98 g) Al + 6 (36.46 g) HCl  2 (133.3 g) AlCl3 + 3 (2.016 g) H
2 al 6 hcl 2 alcl 3 3 h 21
2 Al + 6 HCl  2 AlCl3 + 3 H2
  • How many molecules of HCl will react with 4 atoms of Al?
  • How many atoms of Al are required to make 1 molecule of AlCl3?
  • How many moles of H2 are made from 3 mole of HCl?
  • If 4 moles of AlCl3 are produced, how much H2 is produced?
  • How much HCl is required to react with 1 mole of Al?
ch 4 2 o 2 co 2 2h 2 o
CH4 + 2 O2 CO2 + 2H2O
  • How many moles of oxygen are required to react completely with 50.0 g CH4?
  • What mass of CH4, in grams, is required to react with 96.0 g of O2?
  • Calculate the mass of CO2 that can be produced by burning 6.0 moles of CH4 in excess O2?
  • What mass of CH4 produces 3.01 x 1023 water molecules when burned in excess oxygen?
slide6
Smelling salts contain ammonium carbonate, which can decompose to form ammonia, which acts as a mild heart stimulant. Ammonium carbonate decomposes by the reaction
  • (NH4)2CO3(s)  2 NH3(g) + CO2(g) + H2O(l)
  • How many g of NH3 will be formed from 0.500 g of (NH4)2CO3?
slide7
Calculate the number of moles of calcium chloride needed to react with excess silver nitrate to produce 6.60 g of silver chloride.
  • 1st - write the equation ( a double displacement reaction)
  • 2nd -do stoichiometry
reactions and energy
Reactions and Energy
  •  Reactions will often generate energy (heat) or produce (give off) energy. We can use stoichiometry to calculate energy consumption or production.
slide9
Exothermic reaction -- A reaction that liberates heat.
  • C6H12O6 2 C2H5OH + 2 CO2 + heat
  • Endothermic reaction -- A reaction that absorbs heat.
  • CO2 + heat  C + O2
slide10
Consider the combustion of methane (used in our bunsen burners)
  • CH4(g) + 2 O2(g)  CO2(g) + 2 H2O(l) + 890 kJ
  • Calculate the amount of heat produced when 1.00 g of methane is burned in excess oxygen.
percent yield
Percent Yield
  • % Yield = (mass product/mass expected)*100(%)
  • What could cause the yield to be < 100%?
  • impurities in the sample
  • incomplete reaction
  • What could cause the yield to be > 100%?
  • unexpected reactions
  • Impure product
  • incorrect weighing etc.
slide12
Copper(I)sulfide reacts upon heating in oxygen gas to produce copper metal and sulfur dioxide. How many grams of copper can be obtained from 500.0 g of cuprous sulfide using this process?
  • If 382.6 g of copper were obtained from the reaction above, what would be the percent yield?
  • What mass of sulfur dioxide would be produced from 500.0 grams of cuprous sulfide?
limiting reactant
Limiting reactant
  • Chez Ronald is making Big Macs. The formula for a Big Mac is B3M2, and is made according to the following fast food formula.
  • 2 M + 3 B  B3M2
  • If Chez Ronald buys 28 meats and 36 buns how many Big Macs (B3M2) can he make?
  • We only got 11 Big Macs - What is the percent yield?
2 mn s 3 o 2 g 2 mno 3 s
2 Mn(s) + 3 O2(g)  2 MnO3(s)
  • For the reaction above, compute the theoretical yield of product in moles for each of the following initial amounts of reactants.
  • 2 mol Mn; 2 mol O2
  • 4.8 mol Mn; 8.5 mol O2
slide15
How much potassium chloride is produced from the reaction of 2.00 g potassium and 3.00 g chlorine gas? Which is the limiting reagent? How much of the excess reagent remains?
  • We only recovered 3.66 g KCl. What is the percent yield?
4 al s 3 o 2 g 2 al 2 o 3 s
4 Al(s) + 3 O2(g)  2 Al2O3(s)
  • For the reaction above, how many grams of Al2O3 will be formed from the reaction of 2.29 g of Al with 1.85 g of O2?
  • How many moles of each reactant remain after the reaction?
slide17
When solutions containing 4.28 g Na2SO4 and 7.16 g of BaCl2 are mixed, what mass of BaSO4 is produced?
mg 3 n 2 6h 2 o 3mg oh 2 2nh 3
Mg3N2+6H2O3Mg(OH)2+2NH3
  • How many moles of Mg(OH)2 would be produced from the reaction of 0.10 mole of Mg3N2?
  • How many moles of NH3 would be produced from the reaction of 500 g of Mg3N2?
  • How many molecules of water would be required to react with 3.64 g of Mg3N2?
  • What is the maximum number of grams of Mg(OH)2 that can be produced by the reaction of 10.0 g of Mg3N2 and 14.4 g of H2O?
  • What is the percent yield if 9.4 g of Mg(OH)2 are produced?
ca 5 po 4 3 f h 2 so 4 h 2 o h 3 po 4 caso 4 2h 2 o hf
Ca5(PO4)3F+H2SO4+H2OH3PO4+CaSO4*2H2O+HF
  • Balance the reaction
  • How many moles water to react with 4.32 moles fluoroapatite?
  • How many grams of phosphoric acid will be formed from 493 g fluoroapatite, excess sulfuric acid and water?
  • How much calcium sulfate can be made from 5.00 g fluoroapatite, 5.00 g sulfuric acid, and 5.00 g water? How much of each reagent will remain?
  • If the above reaction yields 6.28 g of calcium phosphate dihydrate, what is the percent yield?