Ch. 14 kinetics                                     test  [100 points]                                             AP chemistry

Show your work in an organized manner, include (i) any relevant equation (or formula), (ii) conversion factor(s), (iii) put the proper units in your calculations and answer, and (iv) have the proper number of significant figures in your answer. 

Academic Honesty:   The answers on this test are my own and I am using only the allowed set of notes as described in the syllabus.  I have not discussed the test questions with anyone before or during the test nor have I seen the test questions prior to the exam.  If you violate any of the preceding items or do not sign, your semester grade is a F.

                                                                        Signature:  ___________________

1. In regards to the reaction:  3 C2H4   -->  C6H12 , ___.  [hint:  it’s the problem in the email; 20 points]

Run          Initial [C2H4]            Rate of formation of C6H12  in   M/min.
1                 0.200 M               2.00 x 10 -3
2                 0.400 M                8.00 x 10 -3
3                 1.00                      5.00 x 10 -2

a. Determine the rate Law, and find the rate constant k.  

b. the initial [C2H4] = 0.500 M; how long does it take to decrease [C2H4] to 0.200 M ?

2.  In regards to your recent kinetics lab involving the reaction:  crystal violet  +  NaOH  →  product, describe the analysis to determine all of the parameters in the rate law of the reaction.  [20 points; hints:  (i) it’s the weekly quiz problem; (ii) rate = k [crystal violet]a [OH -]b; i.e. how to determine the value of k, a, and b and (iii)  use of pseudo-rate law approximation.] 

3.  Describe how to determine the activation energy of a reaction using graphical analysis; include its basis / rationale.  [10 points]

4. Radioactive decay is described by first-order kinetics.  Radioactive dating is a technique to determine the “age” of an object based on measuring the current amount of radioactivity in a sample and estimating the amount of radioactivity in the sample at t = 0. 

A sample currently contains 5.0 mg 14C and 2.0 mg 14N, where 14C is a radioactive isotope, while 14N is not radioactive.  The radioactive decay of 14C forms 14N; assume that there is no other source of 14N in the sample.  The half-life of 14C is 5730 years.  [20 points]

a. What is the decay constant of 14C ?

b.  How many moles of 14C and 14N are currently in the sample ?

c. How many moles of 14C was in the sample at t = 0 ?  [hints:  (i) there was initially no 14N in the sample, i.e. all of the 14N in the sample came from the radioactive decay of 14C, (ii) reaction:  14C  → 14N  +  β - , and (iii) the coefficients in the preceding reaction is 1:1:1; i.e. integrate your knowledge of stoichiometry]

d. What is the “age” of the sample ?  That is, how long did it take for the sample to get to its present state ?

5.  In regards to the reaction:  N2(g)  +  3 H2(g)  →  2 NH3(g), if the activation energy of the forward reaction is 125 kJ, then what is the activation energy of the backward reaction ?  [15 points]

6.  old topics;  [15 points]