Exam2 - solution_pdf - Version 098 EXAM 2 holcombe(51395...

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Version 098 – EXAM 2 – holcombe – (51395) 1 This print-out should have 32 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. Good luck! 001 3.2points The Haber process is the production of am- monia gas (NH3) from nitrogen gas (N2) and hydrogen gas (H2). Be sure to balance the equation before you start! A three-to-one mixture of hydrogen and nitrogen was rapidly pumped into a Haber apparatus until the internal pressure was 60 atm at 350 C. A catalyst was then added, and the system was allowed to reach equilibrium. The internal pressure was 45 atm. What was the partial pressure of the ammonia in the final mixture at 350 C? 1. 15.0 atm correct 2. 30.0 atm 3. 2.0 atm 4. 5.0 atm 5. 7.5 atm Explanation: 002 3.2points Predict whether the equilibria I) CH 4 (g) + H 2 O(g) CO(g) + 3 H 2 (g) , Δ H = +206 kJ II) CO 2 (g) + 2 NH 3 (g) CO(NH 2 ) 2 (s) + H 2 O(g) , Δ H = - 90 kJ will shift toward products or reactants with a temperature increase. 1. Unable to determine 2. I shifts toward reactants and II shifts toward products. 3. I shifts toward products and II shifts to- ward reactants. correct 4. Both I and II shift toward products. 5. Both I and II shift toward reactants. Explanation: If a reaction is exothermic, raising the tem- perature will tend to shift the reaction toward reactants; whereas if the reaction is endother- mic, a shift toward products will be observed. Reaction I is endothermic (+Δ H ); raising the temperature should favor the formation of products. Reaction II is exothermic; raising the temperature should favor the formation of reactants. 003 3.2points What is the main overall driving force for any spontaneous reaction or change? Consider only the reaction system, not the surround- ings. 1. To maximize entropy. 2. To maximize electrostatic interactions. 3. To obey the laws of gravity. 4. To lower the available free energy. cor- rect 5. To release heat energy. Explanation: 004 3.2points Nitric oxide (NO) is a toxic chemical produced in automobile engines. O 2 (g) + N 2 (g) ←→ 2 NO(g) Suppose that at 0 C, K = 0 . 5 and at 10 C, K = 4. Δ H of this reaction is (posi- tive/negative) and it would be best to run an engine as (hot/cold) as possible to reduce emissions of NO. 1. negative; cold 2. positive; hot
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Version 098 – EXAM 2 – holcombe – (51395) 2 3. positive; cold correct 4. negative; hot Explanation: The direct proportionality between temper- ature and K demonstrates that Δ H is posi- tive and to prevent the reaction, the engine should be run as cold as possible. 005 3.2points Which of the following equilibrium reactions is NOT affected by changes in pressure? 1. 2 BrCl(g) Br 2 (g) + Cl 2 (g) correct 2. 2 CO 2 (g) 2 CO(g) + O 2 (g) 3. 2 H 2 O 2 ( ) 2 H 2 O( ) + O 2 (g) 4. H 2 (g) + Br 2 ( ) 2 HBr(g) 5. H 2 (g) + I 2 (s) 2 HI(g) Explanation: 006 3.2points Given K p = 4 . 6 × 10 14 and Δ H 0 = 115 kJ/mol for the reaction 2 Cl 2 (g) + 2 H 2 O(g) 4 HCl(g) + O 2 (g) at 25 C, what is K p at 400 C?
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