hw 7 - shah (rps587) – Homework 7 – mcdevitt –...

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Unformatted text preview: shah (rps587) – Homework 7 – mcdevitt – (52365) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A closed system can exchange energy with the surroundings. 1. True correct 2. False Explanation: A closed system cannot exchange matter with the surroundings; it can exchange en- ergy. 002 10.0 points Work done (by/on) the system is negative, and heat (gained/lost) by the system is posi- tive. 1. on, gained 2. by, lost 3. by, gained correct 4. on, lost Explanation: The sign conventions for process functions (like work and heat) are such that a positive sign is attributed to the system if it gains energy (in the form of heat or work). 003 10.0 points What factor determines whether a reaction will be exothermic or endothermic? 1. the heat properties of the products 2. the difference in energy between reactants and products correct 3. the activation energy of the reaction 4. the relative concentrations of reactants and products in solution 5. the speed of the reaction Explanation: Δ H is the energy difference between the products and reactants; Δ H for exothermic reactions is negative, and Δ H for endother- mic reactions is positive. 004 10.0 points For the reaction 2 H 2 (g) + O 2 (g) → 2 H 2 O(g) find the value for the work done at 300 K. 1. 2.5 kJ correct 2.- 7 . 5 kJ 3.- 2 . 5 kJ 4. 7.5 kJ Explanation: T = 300 K R = 8 . 314 J mol · K w =- P Δ V =- Δ n R T =- (2- 3) mol parenleftbigg 8 . 314 J mol · K parenrightbigg (300 K) = 2494 . 2 J 005 10.0 points Which of the following would definitely result in an increase in the internal energy of a sys- tem? 1. Work done on the surroundings and heat transferred into the system 2. Work done on the surroundings and heat transferred into the surroundings 3. Work done on the system and heat trans- ferred into the surroundings 4. Work done on the system and heat trans- ferred into the system correct Explanation: shah (rps587) – Homework 7 – mcdevitt – (52365) 2 An increase in internal energy of a system would definitely occur if the signs of w and q are both positive. This occurs when work is done on the system and heat is transferred into the system, respectively. 006 10.0 points 1.95 mol of an ideal gas at 300 K and 3.00 atm expands from 16 L to 28 L and a final pressure of 1.20 atm in two steps: (1) the gas is cooled at constant volume until its pressure has fallen to 1.20 atm, and (2) it is heated and allowed to expand against a constant pressure of 1.20 atm un- til its volume reaches 28 L....
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This note was uploaded on 04/29/2009 for the course CH 52365 taught by Professor Mcdevitt during the Spring '09 term at University of Texas at Austin.

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hw 7 - shah (rps587) – Homework 7 – mcdevitt –...

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