# chexam1 - Version 158 – Exam 1 – Holcombe –(52460 1...

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Unformatted text preview: Version 158 – Exam 1 – Holcombe – (52460) 1 This print-out should have 35 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. Helpful constants and conversions 1 atm = 760 torr = 760 mm Hg 0 degC = 273.15 K R = 8.314 J/K*mol R = 0.082 L*atm/K*mol 001 10.0 points Given that CO 2 (g) reacts with C(s) via the reaction C(s) + CO 2 (g) ⇀ ↽ 2 CO(g) and K p = 1.90 atm, what is the equilibrium partial pressure of CO 2 if 1.00 atm of CO 2 is placed in a vessel with PURE SOLID CAR- BON? (Note: There was no CO initially.) 1. 0.55 atm 2. 0.43 atm 3. 0.51 atm correct 4. 0.85 atm 5. 0.60 atm Explanation: K p = 1 . 9 atm C(s) + CO 2 (g) ⇀ ↽ 2 CO(g) ini, atm 1 Δ, atm- x 2 x eq, atm 1- x 2 x K p = P 2 CO P CO 2 = 1 . 9 (2 x ) 2 1- x = 1 . 9 4 x 2 + 1 . 9 x- 1 . 9 = 0 Therefore x =- 1 . 9 ± radicalbig (1 . 9) 2 + 16(1 . 9) 8 = 0 . 491476 P CO 2 = 1- x = 0 . 508524 atm 002 10.0 points The chemical reaction 2 H 2 O + energy → 2 H 2 + O 2 is 1. an ionic reaction. 2. a synthesis reaction. 3. an exothermic reaction. 4. an endothermic reaction. correct Explanation: Energy is required to start the reaction. 003 10.0 points Catalase (a liver enzyme) dissolves in water. A 14 mL solution containing 0 . 166 g of cata- lase exhibits an osmotic pressure of 1 . 2 Torr at 20 ◦ C. What is the molar mass of catalase? 1. 2 . 3 × 10 5 g / mol 2. 1 . 58 × 10 5 g / mol 3. 1 . 81 × 10 5 g / mol correct 4. 1 . 4 × 10 5 g / mol 5. 3 . 16 × 10 5 g / mol 6. 2 . 53 × 10 5 g / mol Explanation: V = 14 mL = 0 . 014 L m = 0 . 166 g T = 20 ◦ C + 273 = 293 K Π = 1 . 2 Torr R = 0 . 08206 L · atm / K / mol Π = n RT V = m MW RT V M = mRT V Π MW = (0 . 166 g) (0 . 08206 L · atm / K / mol) (0 . 014 L)(1 . 2 Torr) × (293 K) parenleftbigg 760 Torr 1 atm parenrightbigg = 1 . 80556 × 10 5 g / mol . Version 158 – Exam 1 – Holcombe – (52460) 2 004 10.0 points Consider the temperature composition dia- grams of two different binary mixtures, but each containing A as one of the compo- nents. Which curve best describes the sit- uation where the more volatile component of the mixture CAN be initially collected in the pure form in the distillate if X A in the boiling pot = 0.5? 1. Neither diagram 2. . 2 . 4 . 6 . 8 1 . 20 40 60 80 100 120 140 X A boilingtemperature( ◦ C) correct 3. . 2 . 4 . 6 . 8 1 . 20 40 60 80 100 120 140 X A boilingtemperature( ◦ C) Explanation: 005 10.0 points What mass of ethylene glycol ((CH 2 OH) 2 with molecular weight 62 g/mol) must be added to 1.00 L of H 2 O (of mass 1 kg) to lower the freezing point to- 5 ◦ C? K f H 2 O = 1 . 86 ◦ C /m . 1. 66 g 2. 167 g correct 3. 25 g 4. 330 g 5. 123 g Explanation: MW CH 2 OH = 62 g/mol V H 2 O = 1 L m H 2 O = 1 kg T f =- 5 ◦ C T f = T f- Δ T f Δ T f = T f- T f = 0 . 00 ◦ C- (- 5 ◦ C) = 5 ◦ C Δ T f = K f · m m = Δ T f K f = 5 ◦ C 1 . 86 ◦ C /m = 2 . 688 m m = n (CH 2 OH) 2 kg water = g (CH 2 OH) 2 MW (CH 2 OH) 2 kg water...
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## This note was uploaded on 09/26/2010 for the course CH 53215 taught by Professor Mccord during the Spring '09 term at University of Texas.

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chexam1 - Version 158 – Exam 1 – Holcombe –(52460 1...

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