FINAL-solutions - Version 174 FINAL sutcliffe (51045) 1...

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Unformatted text preview: Version 174 FINAL sutcliffe (51045) 1 This print-out should have 38 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Calculate the constant A in the Arrhenius equation, given that the second order reac- tion rate constant for a reaction is 1.00 10 3 L/mol s at 500 C and the activation energy E a is 19.87 kcal/mole. 1. 1 . 00 10 7 2. 1 . 00 10 8 3. 4 . 55 10 3 4. 4 . 15 10 8 correct 5. 2 . 4 10 6 Explanation: k = 1 . 10 3 L s mol E a = 19870 cal mol T = 500 C + 273 = 773 K k = Ae E a /RT A = ke E a /RT = ( 1 10 3 ) exp bracketleftbigg 19870 (1 . 987)(773) bracketrightbigg = 4 . 15 10 8 002 10.0 points NOTE: If this helps, the K a for HClO 3 is ENORMOUS!! All components are present in 0.10 M con- centrations. I) HCN and NaCN II) NH 3 and NH 4 Cl III) HNO 3 and NH 4 NO 3 IV) HClO 3 and NaClO 3 Which will give buffer solutions? 1. I and III only 2. I and II only correct 3. II, III and IV only 4. I, III and IV only 5. III and IV only Explanation: Buffers are formed in one of two ways, by combining a weak acid and its conjugate base or by combining a weak base and its conjugate acid. HNO 3 and HClO 3 are both strong acids and cannot be used to make effective buffer solutions. HCN is a weak acid and NaCN is the salt of its conjugate base, CN . NH 3 is a weak base and NH 4 Cl is the salt of its conjugate acid, NH + 4 . Therefore 1 and 2 can be used to make effective buffer solutions. 003 10.0 points HINT: If youre having trouble figuring out the order for one of these then remember: your choices for each reagent are first, second and third. Try trial and error! Three separate experiments were per- formed on the rate of the reaction 3 A 2 + 2 B 2 A 3 B. The measured initial concentrations of A 2 (in moles per liter) are shown below along with the measured initial rates of formation of A 3 B (moles per liter per second). Initial Initial Initial Trial [A 2 ] [B] rate M M M/s 1 1 . 2 2 . 4 8 . 10 8 2 1 . 2 1 . 2 4 . 10 8 3 1 . 8 2 . 4 1 . 8 10 7 What is the order of the reaction? 1. first order in [A 2 ] and first order in [B] 2. second order in [A 2 ] and first order in [B] correct 3. third order in [A 2 ] and second order in [B] Version 174 FINAL sutcliffe (51045) 2 4. first order in [A 2 ] and second order in [B] 5. None of these is correct. Explanation: Rate = k [A 2 ] x [B] y Rate 3 Rate 1 = k [A 2 ] x 3 [B] y 3 k [ A 2 ] x 1 [ B ] y 1 1 . 8 10 7 8 . 10 8 = parenleftbigg 1 . 8 1 . 2 parenrightbigg x parenleftbigg 2 . 4 2 . 4 parenrightbigg y 2 . 25 = 1 . 5 x ln 2 . 25 = x ln 1 . 5 x = ln 2 . 25 ln 1 . 5 = 2 Rate 1 Rate 2 = k [A 2 ] 2 1 [B] y 1 k [ A 2 ] 2 2 [ B ] y 2 8 . 10 8 4 . 10 8 = parenleftbigg 1 . 2 1 . 2 parenrightbigg 2 parenleftbigg 2 . 4 1 . 2 parenrightbigg y 2 1 = 2 y y = 1 004 10.0 points Consider a reaction for which (at 300 K)...
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FINAL-solutions - Version 174 FINAL sutcliffe (51045) 1...

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