Homework 3-solutions

Homework 3-solutions - sung(es24394 – Homework 3 –...

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Unformatted text preview: sung (es24394) – Homework 3 – vanden bout – (51640) 1 This print-out should have 41 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points What is the main overall driving force for any spontaneous reaction or change? 1. To maximize electrostatic interactions. 2. To lower the available free energy. cor- rect 3. To maximize entropy. 4. To release heat energy. 5. To obey the laws of gravity. Explanation: 002 10.0 points When the chemical reaction A + B ⇀ ↽ C + D is at equilibrium, 1. the forward reaction has stopped. 2. the reverse reaction has stopped. 3. both the forward and reverse reactions have stopped. 4. neither the forward nor the reverse reac- tions have stopped. correct 5. all four concentrations are equal. 6. the sum of the concentrations of A and B equals the sum of the concentrations of C and D. Explanation: Chemical equilibrium is dynamic equilib- rium, with both foward and reverse processes occuring at the same rate. 003 10.0 points Equilibria involving species in more than one phase are called 1. homogeneous equilibria. 2. chemical equilibria. 3. heterogeneous equilibria. correct 4. reversible reaction. Explanation: If all components of the equilibrium system are in the same phase, equilibrium is homoge- nous; if more than one phase is represented in the system, equilibrium is heterogenous. 004 10.0 points Write the equilibrium expression for the fol- lowing reaction: 2 NO ( aq ) + 4 H 2 O( ℓ ) ←→ 3 H 2 ( aq ) + 2 H + ( aq ) + 2 NO − 3 ( aq ) 1. K = [ NO ] 2 [ H 2 ] 3 · [ H + ] 2 · [ NO − 3 ] 2 2. K = [ H 2 ] 3 · [ H + ] 2 · [ NO − 3 ] 2 [ NO ] 2 · [ H 2 O ] 4 3. K = [ H 2 ] 3 · [ H + ] 2 · [ NO − 3 ] 2 [ NO ] 2 correct 4. K = [[ H + ] 2 · [ NO − 3 ] 2 [ NO ] 2 5. K = [ NO ] 2 [ H + ] 2 · [ NO − 3 ] 2 Explanation: Set up K , products in the numerator, reac- tants in the denominator, all raised to respec- tive stoichiometric coefficients. 005 10.0 points The following equilibrium exists in a closed container: N 2 ( g ) + O 2 ( g ) ←→ 2 NO( g ) sung (es24394) – Homework 3 – vanden bout – (51640) 2 If the partial pressures of N 2 , O 2 and NO at equilibrium are 1 . 5 atm, 2 . 5 atm and . 75 atm respectively, what is the equilbrium constants? 1. K = 5 2. K = 6.67 3. K = 0.15 correct 4. K = 0.2 Explanation: K = P 2 NO P N 2 · P O 2 = . 75 2 1 . 5 · 2 . 5 = 0 . 15 006 10.0 points K c = 4 . 9 × 10 5 for the reaction A(g) ⇀ ↽ 2 B(g) . What is K c for the reaction 2 B(g) ⇀ ↽ A(g) ? 1. 3 . 40 × 10 − 6 2. 2 . 04 × 10 − 6 correct 3. 9 . 81 × 10 − 6 4. 1 . 59 × 10 − 6 5. 2 . 45 × 10 − 6 Explanation: 007 10.0 points Given the following equilibria and equilibrium constants K 1 CO(g) + H 2 O(g) ⇀ ↽ CO 2 (g) + H 2 (g) K 2 CH 4 (g) + H 2 O(g) ⇀ ↽ CO(g) + 3 H 2 (g) K 3 CH 4 (g) + 2 H 2 O(g) ⇀ ↽ CO 2 (g) + 4 H 2 (g) The correct expression for K 3 in terms of K 1 and K 2 is 1. K 3 = K 1 + K 2 2.2....
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Homework 3-solutions - sung(es24394 – Homework 3 –...

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