Exam 2 Mccord - Version 337 – Exam 2 – McCord –(53215...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Version 337 – Exam 2 – McCord – (53215) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. McCord CH302 This exam is only for McCord’s CH302 class. PLEASE Bubble your EID and Ver- sion Number Correctly! 001 10.0 points Which pH represents a solution with 1000 times higher [OH − ] than a solution with pH of 5? 1. pH = 0.005 2. pH = 3 3. pH = 4 4. pH = 8 correct 5. pH = 6 6. pH = 1 7. pH = 5000 8. pH = 2 9. pH = 7 Explanation: pH = 5 pOH = 14- pH = 14- 5 = 9 [OH − ] = 10 − pOH = 10 − 9 M [OH − ] x = 1000 [OH − ] = (10 3 )(10 − 9 M) = 10 − 6 M pOH x =- log(OH x ) = 6 pH x = 14- pOH x = 14- 6 = 8 002 10.0 points The equilibrium constant K c for the reaction 2 SO 2 (g) + O 2 (g) → 2 SO 3 (g) is 11.7 at 1100 K. A mixture of SO 2 , O 2 , and SO 3 , each with a concentration of 0.015 M, was introduced into a container at 1100 K. Which of the following is true? 1. SO 2 (g) and O 2 (g) will be formed until equilibrium is reached. correct 2. [SO 3 ] = 0.045 M at equilibrium. 3. [SO 3 ] = 0.015 M at equilibrium. 4. [SO 3 ] = [SO 2 ] = [O 2 ] at equilibrium. 5. SO 3 (g) will be formed until equilibrium is reached. Explanation: 003 10.0 points What is the concentration of OH − ions in a 0.40 M solution of KCN? The ionization constant of HCN is 4 . × 10 − 10 . 1. 1 . 26 × 10 − 5 2. 3 . 16 × 10 − 3 correct 3. 6 . 25 × 10 − 5 4. 4 . 08 × 10 − 12 5. 1 . 60 × 10 − 10 Explanation: 004 10.0 points The standard molar Gibbs free energy of for- mation of NO 2 (g) at 298 K is 51.30 kJ · mol − 1 and that of N 2 O 4 (g) is 97.82 kJ · mol − 1 . What is the equilibrium constant at 25 ◦ C for the reaction 2 NO 2 (g) ⇀ ↽ N 2 O 4 (g) ? 1. 7 . 01 × 10 − 9 Version 337 – Exam 2 – McCord – (53215) 2 2. 0.657 3. 9 . 72 × 10 9 4. None of these 5. 6.88 correct 6. 1.00 7. 1 . 02 × 10 − 10 8. 0.145 Explanation: Δ G products = 97 . 82 kJ · mol − 1 Δ G reactants = 51 . 30 kJ · mol − 1 Δ G rxn = summationdisplay n Δ G products- summationdisplay n Δ G reactants = 97 . 82- (2)(51 . 30) = (- 4 . 78 kJ / mol) parenleftbigg 1000 J kJ parenrightbigg =- 4780 J / mol Δ G =- RT ln K K = e − Δ G / ( R T ) = exp bracketleftbigg-- 4780 J / mol (8 . 3145 J / mol · K)(298 K) bracketrightbigg = 6 . 88395 005 10.0 points A certain reaction has Δ H equal to 10.1 kJ/mol. This reaction is normally run at room temperature (25 ◦ C). At what new tem- perature should the reaction be run so that K is 3 times its value at 25 ◦ C? 1. 77 ◦ C 2. 31 ◦ C 3. 151 ◦ C 4. 135 ◦ C correct 5. 65 ◦ C 6. 50 ◦ C 7. 94 ◦ C Explanation: K 2 = 3 K 1 Use the van’t Hoff equation. For the K ’s just put in 3 for K 2 and 1 for K 1 , and use the temperatures as appropriate ( T 1 is room tem- perature, T 2 is the unknown temperature)....
View Full Document

This note was uploaded on 10/21/2009 for the course CH 53395 taught by Professor Lyon during the Spring '09 term at University of Texas.

Page1 / 8

Exam 2 Mccord - Version 337 – Exam 2 – McCord –(53215...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online