HW8 - momin (rrm497) Homework 8 Sutcliffe (53120) 1 This...

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Unformatted text preview: momin (rrm497) Homework 8 Sutcliffe (53120) 1 This print-out should have 18 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points 183.3 mL of an HBr solution reacted exactly with 62.1 mL of 0.0400 M Ca(OH) 2 solution. Calculate the molarity of the HBr solution. 1. 0.0136 M 2. 0.0400 M 3. 0.1084 M 4. 0.0271 M correct 5. 0.0542 M 6. 0.0379 M Explanation: V 1 = 183 . 3 mL V 2 = 62 . 1 mL M 2 = 0 . 0400 M The balanced equation for the reaction is 2 HBr + Ca(OH) 2 CaBr 2 + 2 H 2 O Molarity is moles solute per liter of solution. We know the volume of the HBr solution. If we could find the moles of HBr in the solution we could calculate the molarity. We start by calculating the moles of Ca(OH) 2 present: ? mol Ca(OH) 2 = 62 . 1 mL soln 1 L soln 1000 mL soln . 0400 mol Ca(OH) 2 1 L soln = 0 . 00248 mol Ca(OH) 2 Using the mole-to-mole ratio from the bal- anced chemical equation we calculate the moles of HBr needed to react with this amount of Ca(OH) 2 : ? mol HBr = 0 . 00248 mol Ca(OH) 2 2 mol HBr 1 mol Ca(OH) 2 = 0 . 00497 mol HBr This is the number of moles of HBr needed to react the Ca(OH) 2 and therefore the number of moles present in the 183.3 mL of HBr so- lution. We can calculate the molarity of the HBr solution by dividing the moles of HBr by the volume of the HBr solution: ? M HBr = . 00497 mol HBr . 1833 L soln = 0 . 0271 M HBr 002 10.0 points Calculate the reaction enthalpy for the com- bustion of ethanol CH 3 CH 2 OH + 3 O 2 2 CO 2 + 3 H 2 O given the data C 2 H 2 + 5 2 O 2 2 CO 2 + H 2 O H rxn =- 1300 kJ/mol C 2 H 2 + H 2 C 2 H 4 H rxn =- 175 kJ/mol C 2 H 4 + H 2 O CH 3 CH 2 OH H rxn =- 44 kJ/mol H 2 + 1 2 O 2 H 2 O H rxn =- 286 kJ/mol 1.- 1367 kJ/mol correct 2.- 1761 kJ/mol 3.- 1800 kJ/mol 4. None of these is correct. 5.- 1717 kJ/mol Explanation: 003 10.0 points For which reactions I) O 2 (g) + H 2 (g) H 2 O 2 ( ) II) C(s , diamond) + O 2 (g) CO 2 (g) III) N 2 ( ) + 3 F 2 (g) 2 NF 3 ( ) IV) C(s , graphite) + 3 2 O 2 (g) + H 2 (g) CO 2 (g) + H 2 O(g) V) 2 Fe(s) + 3 2 O 2 (g) Fe 2 O 3 (s) momin (rrm497) Homework 8 Sutcliffe (53120) 2 would H r = H f ? 1. I, II, III, IV and V 2. I and II only 3. I and V only correct 4. II and IV only 5. II, III and IV only 6. IV and V only 7. I, III and V only 8. I, III, IV and V only Explanation: 004 10.0 points Calculate the standard reaction enthalpy for the formation of boron trifluoride, which is widely used in the chemical industry: B 2 O 3 (s) + 3 CaF 2 (s) 2 BF 3 (g) + 3 CaO(s) . The standard enthalpy of formation for BF 3 is- 1137 kJ / mol, for CaO- 635 . 09 kJ / mol, for B 2 O 3- 1272 . 8 kJ / mol, and for CaF 2- 1219 . 6 kJ / mol....
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This note was uploaded on 12/11/2009 for the course CH 301 taught by Professor Fakhreddine/lyon during the Spring '07 term at University of Texas at Austin.

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HW8 - momin (rrm497) Homework 8 Sutcliffe (53120) 1 This...

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