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Unformatted text preview: dang (rtd356) H14: Kinetics 1 Mccord (52450) 1 This print-out should have 16 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points The rate of the reaction 2 O 3 3 O 2 is equal to 1.- [O 2 ] t . 2.- [O 3 ] t . 3.- 1 3 [O 2 ] t . 4. + 1 2 [O 3 ] t . 5.- 1 2 [O 3 ] t . correct 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. none of the other answers is correct 5. 0.015 M s 1 ;- 0.005 M s 1 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 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 =- 1 2 (rate of rxn) 3. [B] t =- (rate of rxn) 4. [B] t = +(rate of rxn) 5. [B] t = +2 (rate of rxn) 6. [B] t = + 1 2 (rate of rxn) 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 004 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? dang (rtd356) H14: Kinetics 1 Mccord (52450) 2 1. R 1 = 2; R 2 = 0; R 3 = 1 2. R 1 = 0; R 2 = 1; R 3 = 2 3. R 1 = 1; R 2 = 2; R 3 = 0 correct 4. R 1 = 1; R 2 = 3; R 3 = 0 5. R 1 = 3; R 2 = 9; R 3 = 1 Explanation: Tripling the concentration of the reactant in R 1 brings about a tripling (= 3 1 ) increase in the rate of the reaction, so the reaction is first order with respect to the reactant in this case....
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