nuclear & kinetics                    test                             [80 points]                   honors Chem

 

For problems involving calculations, show your work in an organized manner, include any relevant equation (or formula and conversion factor(s)), put the proper units in your calculations / answer, and have the proper number of significant figures in your answer.  Clearly identify the problems done and do them in sequence and your answer must begin and end on the same page of paper; otherwise, you will lose points.  attach this sheet to the front of your exam.

 

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:  ___________________

 

Some of the below problems are based on your HW problems.

 

1.  Write the nuclear reaction of  ___.  [15 points]

 

a.  potassium-38 undergoes positron emission

 

b.  sodium-24 decays to magnesium-24

 

c.  plutonium-242 emits alpha radiation

 

d.  a neutron collides into uranium-235 forming 2 neutrons, xenon-135, and __

 

e.  98Mo + 2à  55Cr + __

 

2.  After 1.0 year, the activity of a sample of curium-243 had declined from 3012 disintegrations per second to 2921 disintegrations per second.  What is the half-life of the decay process ?  [10 points]

 

3.  The half-life for the process 238à 206Pb is 4.5 * 109 years.  A mineral sample contains 50.0 mg of 238U and 14.0 mg of 206Pb.  What is the age of the mineral ?  [15 points]

 

4.  fill-in the below table in regards to the combustion of methanol, CH3OH  [10 points]

 

Rate  (M / sec)

Δ [O2 ] / Δt  (mM / s)

Δ [CO2 ] / Δt  (mM / s)

Δ [H2 O] / Δt  (mM / s)

skip

 

 

10.0 mM / s

2.0 * 10-3

 

 

 

 

 

5.  based on the below hypothetical experimental data, determine the rate law, includes the value / units of the rate constant for the reaction:  N2  +  H2  à  NH3  [15 points]

 

Experiment

[N2]  (M)

[H2]  (M)

Rate  (mM / sec)

1

1.0

1.0

10.0

2

1.0

4.0

20.0

3

2.0

9.0

60.0

 

6.  If the activation energy of the synthesis of ammonia from hydrogen and nitrogen (see preceding chemical equation) is 325 kJ, what is the activation energy of the degradation of ammonia ?  Justify your response.  [hint:  use your thermodynamics knowledge; 15 points]