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Unformatted text preview: Version 174 – FINAL – sutcliffe – (51045) 1 This printout should have 38 questions. Multiplechoice 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 you’re 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) Δ...
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This note was uploaded on 03/26/2012 for the course CHEM 302 taught by Professor Mccord during the Fall '10 term at University of Texas.
 Fall '10
 McCord
 Chemistry

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