Ch. 14  kinetics                                   test                   70 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. Radioactive decay is described by 1st order kinetics.  14C is a radioactive isotope and has a half-life of 5,730. years. [15 points]

a.  What is the decay constant ?

b. What is the equation describing the amount of radioactive isotope in a sample as a function of time ?

c.  A sample originally had 25.0 mg 14C, but now has only 5.00 mg 14 C.  What is the “age” of the sample ?  That is, how much time elapsed for this change in the amount of 14C to occur ?

2. The rate law for a hypothetical reaction is:  rate = k [A]2.   [15 points]

a. If the rate = 1.0 mM / sec at [A] = 2.0 M, then what is the value and units of the rate constant ?

b. What is the rate of the reaction at [A] = 1.75 M ?

c. How much time would it take for a 2.0 M solution to become 0.5 M ?

3. Describe the graphical analysis to determine if a reaction consisting of a single reactant (i) follows 0th, 1st, or 2nd order kinetics, (ii) how to determine the value of its rate constant and (iii) what is the units of the rate constant ?  [10 points]

4. What is a pseudo-rate law in the context of a reaction with two reactants, C and D ?   What is the basis / rationale of a pseudo rate law ?  [5 points]

5. In regards to the reaction:   ethane  +  oxygen  gas  →  carbon dioxide  +  water.  [15 points]

a. Write balanced chemical equation using the lowest ratio of integers

b. Write the rate law for the reaction.

c. If the rate of the reaction = 1.0 mM / second, then __

d.  If 1.0 mM / second, then 6. Doubling the temperature of a reaction from 15 ºC to 30. ºC, doubles the rate of the reaction.  What is the value of the activation energy of the reaction ?  [10 points]