2 - Elbel Brittany – Homework 2 – Due noon – Inst J A...

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Unformatted text preview: Elbel, Brittany – Homework 2 – Due: Jan 30 2006, noon – Inst: J A Holcombe 1 This print-out should have 19 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. The grading on homework has been changed to allow more than one guess. Good luck! 001 (part 1 of 1) 10 points Calculate ΔG ◦ r for the decomposition of mer- cury(II) oxide 2HgO(s) → 2Hg( ‘ ) + O 2 (g) Δ H ◦ f- 90 . 83-- (kJ · mol- 1 ) Δ S ◦ m 70 . 29 76 . 02 205 . 14 (J · K- 1 · mol- 1 ) at 298 K. 1.- 246.2 kJ · mol- 1 2.- 64.5 kJ · mol- 1 3. +246.2 kJ · mol- 1 4. +117.1 kJ · mol- 1 correct 5.- 117.1 kJ · mol- 1 Explanation: 002 (part 1 of 1) 10 points The standard free energy of formation of CS 2 ( ‘ ) is 65.27 kJ · mol- 1 at 298 K. This means that at 298 K 1. CS 2 ( ‘ ) has a negative entropy. 2. CS 2 ( ‘ ) is thermodynamically unstable. correct 3. CS 2 ( ‘ ) is thermodynamically stable. 4. CS 2 ( ‘ ) will not spontaneously form C(s) + 2S(s). 5. No catalyst can be found to decompose CS 2 ( ‘ ) into its elements. Explanation: 003 (part 1 of 1) 10 points Consider the following reaction: CO(g) + Cl 2 (g) → COCl 2 (g) Species ΔH f S kJ/mol J/mol · K CO- 110 . 5 197 . 6 Cl 2 . 223 . COCl 2- 223 . 289 . 2 Calculate Δ G for the reactions at 298 K. 1.- 73 . 34 kJ/mol correct 2.- 500 . 0 kJ/mol 3.- 7 . 3 J/mol 4. 221 . 1 kJ/mol Explanation: 004 (part 1 of 1) 10 points A thermodynamically favorable reaction 1. if also kinetically favorable, proceeds at a detectable rate. 2. is called spontaneous but doesn’t neces- sarily proceed at a detectable rate. 3. All choices are correct. correct 4. has negative Δ G . Explanation: A reaction is spontaneous (favorable) when Δ G is negative. Just because a reaction is thermodynamically favorable doesn’t mean that it proceeds fast enough to be detected. Only when a reaction is kinetically favorable can it be detected....
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2 - Elbel Brittany – Homework 2 – Due noon – Inst J A...

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