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Unformatted text preview: Page 1 Exam I master 4/10/2008 12:19:16 AM http://www.chem.arizona.edu/~kellerp/exams/Exam1/Exam1Ban/Exam1Ban.htm Chemistry 103B Exam 1 Answer Key Form B 1. (2) When a chemical reaction has reached equilibrium (a) the reaction quotient Q has reached a minimum (b) the concentrations of the reactants have become equal to the concentrations of the products (c) the concentrations of the reactants have all reached 0 mol/L (d) the concentrations of reactants and products have reached constant values (e) the forward and reverse reactions have both stopped 2. (2) Shown below are the elementary steps in the mechanism of a gas phase reaction BC(g) B(g) + C(g) [slow] B(g) + A(g) AB(g) [fast] C(g) + A(g) AC(g) [fast] AB(g) + AC(g) A 2 BC(g) [fast] If more molecules of A are added (a) the rate will increase (b) the rate willbe unchanged (c) the rate will decrease (d) the activation energy will decrease (e) the activation energy will increase 3. (2) In a period of 355s the concentration of BC(g) in the above reaction dropped from0.500mol/L to 0.250mol/L. How long would it take for the concentration of BCto drop from0.250to 0.125mol/L? The mechanism clearly shows the slow step is unimolecular For such reactions the half-lifeis constant Page 2 Exam I master 4/10/2008 12:19:16 AM http://www.chem.arizona.edu/~kellerp/exams/Exam1/Exam1Ban/Exam1Ban.htmhttp://www....
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