hw 6 - Garg, Pallavi – Homework 6 – Due: Dec 5 2007,...

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Unformatted text preview: Garg, Pallavi – Homework 6 – Due: Dec 5 2007, 2:00 am – Inst: Donna C Lyon 1 This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. This HW assignment is due Wednesday, December 5 by 2:00AM. DO NOT WAIT UNTIL THE LAST HOUR TO TURN IN YOUR HOMEWORK ANSWERS. KEEP UP WITH THE MATERIAL BY ANSWER- ING QUESTIONS AS THEY ARE COV- ERED IN CLASS. 001 (part 1 of 1) 10 points Which one of the following statements is true? 1. Spontaneous reactions always have Δ H ◦ r < 0. 2. A thermodynamically stable compound is a compound with a negative standard free energy of formation. correct 3. Labile is a term that refers to the thermo- dynamic tendency of a substance to decom- pose. 4. Spontaneous reactions always have Δ G ◦ r > 0. 5. Spontaneous reactions always have Δ S ◦ r > 0. Explanation: 002 (part 1 of 1) 10 points In which example is the entropy of the initial state greater than the entropy of the final state? 1. A lump of sugar dissolves in a cup of warm water. 2. A building collapses during an earth- quake. 3. Liquid water evaporates. 4. Liquid water freezes into ice. correct Explanation: Entropy is a measure of disorder on a molecule scale. Solids are more ordered than liquids. 003 (part 1 of 1) 10 points When a liquid boils, which of the following statements is true? 1. Δ T < 2. Δ S < 3. Δ T > 4. Δ S > correct Explanation: Gas phase molecules have more energy and freedom of motion than liquid phase molecules, so gases are more random. Boil- ing causes a system to go from a less random state to a more random state. Δ S is positive when disorder (randomness) increases. T is constant during phase changes. 004 (part 1 of 1) 10 points For the reaction, CH 4 (g) → CH 3 (g) + H(g) what algebraic sign would Δ S carry? 1. Δ S > correct 2. Δ S = 0 3. Δ S < 4. Cannot tell from the information given. Explanation: Entropy ( S ) is high for systems with high degrees of freedom, disorder or randomness and low for systems with low degrees of free- dom, disorder or randomness. In this reaction, 1 mole of gaseous reactant forms 2 moles of gaseous product. 2 moles of gas have more degrees of freedom, disor- der and randomness than 1 mole. Therefore Δ S > 0. Garg, Pallavi – Homework 6 – Due: Dec 5 2007, 2:00 am – Inst: Donna C Lyon 2 005 (part 1 of 1) 10 points Which one shows the substances in the in- creasing order of their molar entropy? 1. None of these 2. CO 2 (g), Ar(g), Ne(g), H 2 O( ‘ ) 3. H 2 O( ‘ ), Ar(g), Ne(g), CO 2 (g) 4. H 2 O( ‘ ), Ne(g), Ar(g), CO 2 (g) correct 5. H 2 O( ‘ ), CO 2 (g), Ne(g), Ar(g) 6. CO 2 (g), H 2 O( ‘ ), Ne(g), Ar(g) Explanation: For H 2 O entropy increases going from a solid to a liquid to a gas. We would auto- matically expect C(s,diamond) to have less entropy than any liquid. Water is a molecu- lar substance held together in the solid phase by weak hydrogen bonds, and the carbons in...
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This note was uploaded on 09/17/2009 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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hw 6 - Garg, Pallavi – Homework 6 – Due: Dec 5 2007,...

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