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UNIT VII

UNIT VII. Stoichiome-tree Lesson 1. VII.1 Coefficients in a Reaction Equation:. Stoichiometry : The relationship between the amount of reactants used in a chemical reaction and the amounts of products produced by the reaction. VII.1 Coefficients in a Reaction Equation:.

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UNIT VII

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  1. UNIT VII Stoichiome-tree Lesson 1

  2. VII.1 Coefficients in a Reaction Equation: Stoichiometry: The relationship between the amount of reactants used in a chemical reaction and the amounts of products produced by the reaction

  3. VII.1 Coefficients in a Reaction Equation: 2Mg + O2 → 2MgO • The coefficient 2, means two magnesium atoms react with one oxygen molecule to produce two molecules of magnesium oxide • if you double the amounts of Mg and O2, what will happen to the amount of MgO??? • if you use 10 times the amount of reactants, what will happen to the amount of MgO???

  4. VII.1 Coefficients in a Reaction Equation: • *the balanced equation describes the ratio in which the substances combine • In terms of MOLES: 2(6.02 x 1023)Mg + (6.02 x 1023)O2 → 2(6.02 x 1023)MgO • 2 mol Mg + 1 mol O2 → 2 mol MgO • The ratio

  5. VII.1 Coefficients in a Reaction Equation: Ex: Consider the reaction equation 2Na + Cl2 → 2 NaCl a.)How many atoms of Na are required to react with 10 molecules of Cl2? b.) How many moles of NaCl are produced when 15 mol of Na are reacted? • p. 124 #1-5

  6. VII.1 Coefficients in a Reaction Equation: Consider the reaction equation:

  7. VII.2 Stoichiometry Calculations involving Moles, Mass, and Gas Volume and Molecules • * A chemical equation is written in terms of moles of reactants and products • To predict the moles of each substance, you can use the mole ratio • Stoichiometry calculations allow you to calculate the amount of CHEMICAL #1 involved in a reaction, based on the amount of CHEMICAL #2

  8. VII.2 Stoichiometry Calculations involving Moles, Mass, and Gas Volume and Molecules From UNIT 5 ( The Mole Unit) , we know how to get from L to moles, g to moles, molecules to moles etc.... • MOLES are the way to go from CHEMICAL #1 to CHEMICAL #2 MOLES of MOLES of CHEMICAL CHEMICAL #1 #2 • ALWAYS convert your values into moles ---- then cross the mole bridge!!

  9. In other words… ANYTIME AT ALL, you are asked to calculate a mass, # of molecules, or a volume between TWO chemicals, each on one side of the equation, you MUST change it first into moles,second use the mole ratio between these two chemicals you have, then third change back to whatever units the question wants! units u have  moles  mole ratio units you want

  10. VII.2 Stoichiometry Calculations involving Moles, Mass, and Gas Volume and Molecules Ex #1: How many moles of sodium metal would be needed to react with chlorine gas and make 737 g of sodium chloride? 2Na + Cl2 → 2NaCl

  11. VII.2 Stoichiometry Calculations involving Moles, Mass, and Gas Volume and Molecules Ex: #2 How many grams of potassium chloride, KCl, are produced by decomposing118 g of potassium chlorate, KClO3?

  12. VII.2 Stoichiometry Calculations involving Moles, Mass, and Gas Volume and Molecules TRY C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l) A sample of propane is burned, what mass of H2O(l) is produced if the reaction also produces 50.0L of CO2(g) at STP?

  13. VII.2 Stoichiometry Calculations involving Moles, Mass, and Gas Volume and Molecules Ex: #3 Consider the reaction… 4NH3 + 5O2 → 6H2O + 4NO How many molecules of NH3 are required to react with 3.00 mol of O2(g)?

  14. VII.2 Stoichiometry Calculations involving Moles, Mass, and Gas Volume and Molecules TRY: 2NH3(aq) + NaOCl(aq) → N2H4(aq) + NaCl(aq) + H2O(l) If 1.25 x 104 kg of N2H4 is produced, how many litres of ammonia gas, at STP, is required in the reaction?

  15. VII.3 Stoichiometry Calculations Involving Molar Concentration Molar Concentration: c = n/V • Only use 22.4L/mol if it is a gas at STP

  16. VII.3 Stoichiometry Calculations Involving Molar Concentration Ex: # 1 If copper wire is put in a solution of silver nitrate, how many grams of copper will react to completely replace silver from 208 mL of 0.100M solution of silver nitrate, AgNO3?

  17. VII.3 Stoichiometry Calculations Involving Molar Concentration Ex: #2 For the reaction: Zn + 2HCl → ZnCl2 + H2 a) What volume of 3.00 M HCl is required to react with 12.35g of zinc?

  18. VII.3 Stoichiometry Calculations Involving Molar Concentration Ex: #2 (continued) For the reaction: Zn + 2HCl → ZnCl2 + H2 b)How many moles of hydrogen are produced when 12.35g of zinc are reacted with the correct amount of HCl?

  19. VII.3 Stoichiometry Calculations Involving Molar Concentration Ex: #3 What volume of CO2(g) at STP is produced if 2.30 L of 0.5 M HCl reacts with an excess of CaCO3?

  20. VII.3 Stoichiometry Calculations Involving Molar Concentration TITRATIONS Definition: a process used to determine the unknown concentration of a solution (SAMPLE) by reacting it with a measured amount of a solution with known concentration (STANDARD) until a desired equivalence point is reached. Usually, it is an acid-base titration.

  21. VII.3 Stoichiometry Calculations Involving Molar Concentration Equivalence Point = Stoichiometric Point Point in titration where the ratio of the moles of each species involved exactly equals the ratio of the coefficients of the species in the balanced reaction equation Ratio of COEFFICIENTS = Ratio of MOLES PRESENT @ this point the indicator changes colour

  22. VII.3 Stoichiometry Calculations Involving Molar Concentration Ex: #1 H3PO4 + 2KOH → K2HPO4 + 2H2O What volume of 0.500 M KOH is required to react with 125mL of 0.300 M H3PO4 in order to produce a solution of K2HPO4?

  23. VII.3 Stoichiometry Calculations Involving Molar Concentration Ex: #2 H3PO4 + 2KOH → K2HPO4 + 2H2O If 19.8 mL of H3PO4 with an unknown molarity react with 25.0 mL of 0.500 M KOH, according to the above reaction, what is the molarity of the H3PO4?

  24. VII.3 Stoichiometry Calculations Involving Molar Concentration TRY H2SO4 + 2NaOH → Na2SO4 + 2H2O If 20.8 mL of H2SO4 with an unknown molarity react with 23.0 mL of 0.400 M NaOH, according to the above reaction, what is the molarity of the H2SO4?

  25. HOMEWORK • Meaning of coefficients: p. 124 # 2, 3. • Stoichiometry: p. 127 # 6,7,8,9,12 • Molar Concentrations: p. 131 # 17-24.

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