Exam 1-solutions

# Exam 1-solutions - Version 026 – Exam 1 – sutcliffe...

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Unformatted text preview: Version 026 – Exam 1 – sutcliffe – (51045) 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 Consider the reaction 2 Fe 2 O 3 (s) + 3 C(s) → 4 Fe(s) + 3 CO 2 (g) Δ H ◦ = 462 kJ / mol Δ S ◦ = 558 J / molK Calculate the equilibrium constant for this reaction at 525 ◦ C. 1. 8 . 15 × 10 − 2 correct 2. 1 . 51 × 10 − 17 3. 3 . 04 × 10 − 3 4. 1 . 9 × 10 6 5. 1 . 23 × 10 1 6. 2 . 18 × 10 − 2 Explanation: Δ G = 462000- (798 . 15 K) (558) = +16632 . 3 J K = e − Δ G/ ( R T ) = e − 2 . 5064 = 8 . 1558 × 10 − 2 002 10.0 points Water vapor condensing to liquid water is what type of process? 1. exothermic correct 2. endothermic 3. isotopic 4. enthalpic Explanation: 003 10.0 points What is the Tyndall effect? 1. the ability to scatter light correct 2. the ability to exist as a rainbow of colors 3. the ability to make fog 4. the ability to form a gel Explanation: A characteristic property of colloids, their ability to scatter light, is called the Tyndall effect. 004 10.0 points The phase diagram for a pure substance is given below. Solid Liquid Vapor 50 100 150 200 250 300 100 200 300 400 Temperature, K Pressure,atm The solid sublimes 1. if warmed at any pressure below 50 atm. correct 2. at 300 K and 100 atm. 3. at 200 K and 100 atm. 4. at 400 K and 200 atm. 5. at 300 K and 75 atm. Explanation: 005 10.0 points The vaporization of water from the liquid Version 026 – Exam 1 – sutcliffe – (51045) 2 state would involve the destruction of in- termolecular hydrogen bonds between water molecules but would still leave each water molecule intact. 1. False 2. True correct Explanation: H 2 O hydrogen bonds with neighboring wa- ter molecules. These bonds must be overcome for a molecule to escape liquid phase and be- come vapor. H 2 O molecules must remain intact. Phase changes are physical changes, not chemical changes. 006 10.0 points If the reaction quotient Q for some hypothet- ical reaction is 100, how does Δ G compare to Δ G ? 1. Δ G > Δ G correct 2. Δ G = Δ G 3. Δ G < Δ G 4. There is insufficient information given to determine the answer. Explanation: Δ G = Δ G + RT ln Q If Q = 100, then the natural log term will be positive. This means that the non standard value of Δ G will be bigger (more positive) than the value of Δ G . 007 10.0 points The partial pressure of CO 2 in the atmosphere is 3 . 9 × 10 − 4 atm. When drinking soda is put in a can, assume that there is 2.0 atm CO 2 in the 2.0 mL gas space above the soda. (The actual CO 2 pressure varies with type of soda.) What is the approximate ratio of the molar concentrations of CO 2 (aq) in the soda before it is opened to that in the soda after it has been opened and reached equilibrium with the surrounding atmosphere; i.e. , has “gone flat?” 1. 5 × 10 3 correct 2. 2 × 10 − 4 3. 2 × 10 2 4. You need Rault’s Law constant for CO...
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## This note was uploaded on 11/17/2011 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas.

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Exam 1-solutions - Version 026 – Exam 1 – sutcliffe...

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