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2006 Exam 2

# 2006 Exam 2 - CHE132 Midterm 2 Form 0 CHE132 Midterm 2...

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CHE132 Midterm 2 Form 0 1 CHE132 Midterm 2 Spring 2006 Form 0 There are 20 multiple choice questions each worth 5 points. The entire exam counts 100 points toward your course total. Constants The Gas constant = R = 8.314 J mol -1 K -1 The Gas constant = R = 0.0821 L atm mol -1 K -1 The molar mass of water is 18.02 g mol -1 The density of liquid water is 1 g/mL. 1 atm = 1.013 x 10 5 Pa. 1 cm 3 = 1 x10 -3 L = 1 x 10 -6 m 3 Equations For a first order reaction: ln([A] o /[A]) = kt For a second order reaction: 1/[A] – 1[A] o = kt reaction = coeff p f (products) - coeff r f (reactants) G° = -RTlnK eq G° = H° - T G reaction = reaction + RTlnQ k = Ae -Ea/RT Quadratic Equation ax 2 + bx + c = 0 x b b ac a 2 4 2

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CHE132 Midterm 2 Form 0 2 Question 1. The experimentally determined rate law for a reaction that involves two reactants, A and B, is: Rate = k[A][B] 1/2 Which one of the following statements is not correct? A: The reaction is first order in A. B: The first elementary reaction in the overall mechanism is not the rate determining step. C: k is the rate constant for the reaction. D: The rate will increase by a factor of 2 if the concentration of B is doubled. E: The rate law cannot be determined from the balanced equation for the overall reaction. Answer D Question 2. A reaction has a rate constant (k) of 4.0 x 10 -6 M -1 s -1 at 25 C. Given that the activation energy (E a ) for the reaction is 50 kJ mol -1 , calculate the rate constant at 300 C. Assume that A (the frequency factor) has the same value at 25 C and 300 C A: 6.4 x 10 -2 M -1 s -1 B: 7.0 x 10 -1 M -1 s -1 C: 4.8 x 10 -5 M -1 s -1 D: 1.1 x 10 -3 M -1 s -1 E: 4.0 x 10 -6 M -1 s -1 Ea = 50000 = 8.314 x ln(k 2 / 4 x 10 -6 ) / (1/298 – 1/573) ln(k 2 / 4 x 10 -6 ) = 9.6855, so k 2 = 0.0643
CHE132 Midterm 2 Form 0 3 Question 3. Iodide ion ( I - ) can be oxidized by hydrogen peroxide (H 2 O 2 ) in acidic solution to form iodine ( I 2 ) and water according to the balanced equation: 2I - (aq) + H 2 O 2 (aq) + 2H 3 O + (aq) I 2 (aq) + 4H 2 O(l) A proposed mechanism for this reaction is shown below and is comprised of three elementary reactions: Which one of the following statements is not correct ? A: Step 1 is the rate determining step. B: HOI is an intermediate. C: The proposed mechanism is consistent with the experimentally determined rate law which is: Rate = k[ I - ][ H 2 O 2 ] D: Step 2 is a bimolecular reaction. E: The activation energy (E a ) for step 1 is smaller than the activation energy for step 2. Answer E

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CHE132 Midterm 2 Form 0 4 Question 4. Formaldehyde (CH 2 O) is formed by reaction of ozone with ethylene: C 2 H 4 (g) + O 3 (g) 2CH 2 O(g) + ½O 2 (g) In order to experimentally investigate the mechanism of this reaction, the following data were collected: Initial Concentration (mol L -1 ) [O 3 ] [C 2 H 4 ] Initial rate of formation of CH 2 O (mol L -1 s -1 ) 0.50 x 10 -7 1.0 x 10 -8 1.0 x 10 -12 1.5 x 10 -7 1.0 x 10 -8 3.0 x 10 -12 1.0 x 10 -7 2.0 x 10 -8 4.0 x 10 -12 Use the information in the Table to calculate the rate constant (k) for the reaction.
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2006 Exam 2 - CHE132 Midterm 2 Form 0 CHE132 Midterm 2...

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