EXAM 6 - This print-out should have 16 questions...

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Johnson, Chelsea – Homework 11 – Due: Apr 25 2007, 11:00 pm – Inst: Walker 1 This print-out should have 16 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. Read all of the options before choosing one. There may be cases in which more than one response appears to be true. PICK THE RE- SPONSE THAT BEST answers the question asked. 001 (part 1 of 1) 3 points Which of the following statements about re- acting molecules is true? 1. The transition state energy is usually the average between the energies of the reactants and products. 2. All molecules in a gas sample at a specific temperature have the same energy. 3. When two reactant molecules collide they must react. 4. An effective collision between two molecules must be oriented correctly. cor- rect Explanation: A collision between molecules results in a reaction if they collide with enough energy and an effective orientation. 002 (part 1 of 1) 3 points Activation energy for an elementary process 1. is part of the net enthalpy change for the reaction. 2. is the energy required to produce the transition state from the reactants. correct 3. is smaller for slower reactions and larger for faster reactions. 4. None of these Explanation: E a reactants products transition state Reaction progress Potential energy When the reactants gain enough energy to equal the energy of activation the transition state is formed. 003 (part 1 of 2) 3 points Consider the following potential energy dia- gram. 40 80 120 160 energy, kJ reaction progress A + B AB What is the value of Δ H ? Correct answer: - 30 kJ. Explanation: The final energy for AB is 50 kJ. The initial energy for A + B is 80 kJ. Δ H = final - initial = 50 - 80 = - 30 kJ 004 (part 2 of 2) 3 points What is the activation energy E a for this re- action? Correct answer: 100 kJ. Explanation: The maximum energy (top of “hill”) is 180 kJ. The initial energy for A + B is 80 kJ.
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Johnson, Chelsea – Homework 11 – Due: Apr 25 2007, 11:00 pm – Inst: Walker 2 E a = maximum - initial = 180 - 80 = 100 kJ 005 (part 1 of 1) 3 points The overall reaction NO 2 (g) + CO(g) NO(g) + CO 2 (g) is proposed to proceed by the mechanism 2 NO 2 (g) NO 3 (g) + NO(g) slow NO 3 (g) + CO(g) NO 2 (g) + CO 2 (g) fast Which of the following rate laws would be consistent with this mechanism?
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