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Unformatted text preview: dsj294 hw11 Holcombe (53570) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. R = 8 . 314 J mol 1 K 1 1 cal = 4.184 J 001 10.0 points The rate of the reaction 2 O 3 3 O 2 is equal to 1. + 1 2 [O 3 ] t . 2.- 1 2 [O 3 ] t . correct 3.- [O 3 ] t . 4.- 1 3 [O 2 ] t . 5.- [O 2 ] t . Explanation: The rate of a chemical reaction can either be expressed as the rate of disappearance of a reactant (as in this case) or as the rate of appearance of a product. However, this rate is multiplied by the inverse of the coef- ficient of the species in question. The nega- tive sign here reminds us that as the reaction progresses, this species is consumed and de- creases in concentration. 002 10.0 points When the reaction 3 NO(g) N 2 O(g) + NO 2 (g) is proceeding under conditions such that 0.015 mol/L of N 2 O is being formed each second, the rate of the overall reaction is ? and the rate of change for NO is ? . 1. 0.030 M s 1 ;- 0.005 M s 1 2. 0.015 M s 1 ;- 0.045 M s 1 correct 3. 0.015 M s 1 ; +0.045 M s 1 4. 0.015 M s 1 ;- 0.005 M s 1 5. none of the other answers is correct Explanation: Notice that three moles of NO are required to make one mole of N 2 O in this reaction, so the rate of disappearance of NO (which has a negative sign) is three times the rate of appearance of N 2 O. 003 10.0 points Which of the following does not affect the rate of a reaction? 1. the value of E a 2. the presence of a catalyst 3. the value of H rxn correct 4. the temperature of the reactants Explanation: H is a state function; it is independent of the path. 004 10.0 points Consider the irreversible reaction A + 2 B 3 C . Which of the following correctly expresses the rate of change of [B] ? 1. [B] t =- 2 (rate of rxn) correct 2. [B] t = +(rate of rxn) 3. [B] t =- 1 2 (rate of rxn) 4. [B] t =- (rate of rxn) 5. [B] t = + 1 2 (rate of rxn) 6. [B] t = +2 (rate of rxn) dsj294 hw11 Holcombe (53570) 2 Explanation: As B is a reactant and consequently disap- pears during the reaction, its rate of change will be negative and the inverse of the coeffi- cient is used when writing the rate: (rate of rxn) =- 1 2 [B] t- 2 (rate of rxn) = [B] t 005 10.0 points Suppose a compound is involved in three different reactions denoted R 1 , R 2 , and R 3 . Tripling the concentration of this reactant in all three reactions causes the rates of reaction to increase by factors of 3, 9, and 1, respec- tively. What is the order of each reaction with respect to this reactant?...
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- Spring '07