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Unformatted text preview: CHEM 614 Unit 12 Crib Discussion Questions 1) For the reaction: NH 4 + (aq) + NO 2- (aq) b N 2 (g) + 2H 2 O(l) At 25 o C, the rate constant is 3.0 x 10-4 M-1 s-1 . a) Write the rate law for this reaction. Rate = k [NH 4 + ] x [NO 2- ] y Without data about the reaction we cannot know what the exponents x and y are for the rate law. b) Calculate the rate of the reaction at this temperature if [NH 4 + ] = 0.26 M and the [NO 2- ] = 0.020 M. To calculate the actual rate we will have to make an assumption about the exponents for the ammonium and nitrite ions. If we assume that the exponents are 1 (first order reactions): Rate = k [NH 4 + ] [NO 2- ] = 3.0 x 10-4 M-1 s-1 )(0.26 M)(0.020 M) = 1.6 x 10-6 M s-1 2) When the concentration of 2-bromo-2-methylpropane is doubled, the rate of the reaction C 4 H 9 Br(aq) + OH- (aq) b C 4 H 9 OH(aq) + Br- (aq) increases by a factor of 2. When the concentrations of both 2-bromo-2-methylpropane and hydroxide ions are doubled, the rate increase is the same, a factor of 2. What are the reactant orders and the overall order of the reaction? The 2-bromo-2-methylpropane is first order. The hydroxide ions are zero order. 3) List four factors that can influence the rate of a reaction. Concentration Temperature Surface area Catalyst 4) When 6 g of granulated Zn is added to a solution of 2 M HCl in a beaker at room temperature, hydrogen gas is generated. For each of the following changes (at constant volume of the acid) state whether the rate of hydrogen gas evolution will be increased, decreased, or unchanged and provide an explanation: i) 6 g of powdered Zn is used H 2 gas evolution will be increased because the surface area of the Zn has been increased ii) 4 g of granulated Zn is used H 2 gas evolution will be decreased because the surface area of the Zn has been decreased iii) 3 drops of NaOH are added to the HCl before adding to the Zn H 2 gas evolution will be decreased because the concentration of HCl has been decreased iv) The temperature is raised to 40 o C....
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