Exam 1-solutions

# Exam 1-solutions - Version 429 – Exam 1 – sutcliffe –...

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Unformatted text preview: Version 429 – 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 An unknown liquid has a vapor pressure of 88 mmHg at 45 ◦ C and a heat of vaporization of 32 kJ / mol, what is its vapor pressure at 55 ◦ C? 1. 156 mmHg 2. 61 mmHg 3. 89 . 4 mmHg 4. 127 mmHg correct Explanation: Use the Clausius-Clapeyron Equation. Here, the only thing we don’t know is P 2 . ln parenleftbigg P 2 P 1 parenrightbigg = Δ H vap R parenleftbigg 1 T 1- 1 T 2 parenrightbigg ln parenleftbigg P 2 88 parenrightbigg = 32 , 000 8 . 31 parenleftbigg 1 318- 1 328 parenrightbigg ln P 2 = 32 , 000 8 . 31 parenleftbigg 1 318- 1 328 parenrightbigg + ln 88 P 2 = e 4 . 84 = 127 mmHg 002 10.0 points Water vapor condensing to liquid water is what type of process? 1. isotopic 2. exothermic correct 3. enthalpic 4. endothermic Explanation: 003 10.0 points In which of the following cases will the LEAST time be required to arrive at equilibrium? K below refers to the equilibrium constant. 1. K is about 1. 2. K is a very small number. 3. Cannot tell since the time to arrive at equilibrium does not depend on K . correct 4. Cannot tell without knowing the value of K . 5. K is a very large number. Explanation: The equilibrium constant K reflects the relative amounts of products and reactants present when the reaction is complete, and gives no information on the time needed. The rate constant k indicates how fast the reaction occurs. 004 10.0 points Assuming all of the following salts dissolve completely in water, which one would be the best to use if you were trying to raise the boiling point of the solution? 1. Na 3 PO 4 2. KNO 3 3. NaCl 4. (NH 4 ) 2 Cr 2 O 7 5. Al 2 (SO 4 ) 3 correct Explanation: Al 2 (SO 4 ) 3 is highly soluble and produces 5 ions upon dissolving, has the largest van’t hoff coefficient and is the best choice for at- tempting raise a solution’s boiling point. 005 10.0 points Which of the following is likely to be LEAST soluble in water? 1. C 6 H 12 O 6 (glucose). Version 429 – Exam 1 – sutcliffe – (51045) 2 2. C 6 H 6 (benzene). correct 3. HCHO (formaldehyde). 4. CH 3 OH (methanol). Explanation: 006 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. 2 . 18 × 10 − 2 3. 3 . 04 × 10 − 3 4. 1 . 23 × 10 1 5. 1 . 51 × 10 − 17 6. 1 . 9 × 10 6 Explanation: Δ G = 462000- (798 . 15 K) (558) = +16632 . 3 J K = e − Δ G/ ( R T ) = e − 2 . 5064 = 8 . 1558 × 10 − 2 007 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...
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## This note was uploaded on 03/26/2012 for the course CHEM 302 taught by Professor Mccord during the Fall '10 term at University of Texas.

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Exam 1-solutions - Version 429 – Exam 1 – sutcliffe –...

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