Nuclear chem. & kinetics  test              [85 points]                Honors chemistry

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. 

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.  Write the nuclear equation for  __ / fill-in the blank.   [15 points]

a.  alpha decay of tin - 120:  ____________________________

b.  positron emission of  phosphorus – 32:  _________________________

c.   235 U  -->  2 neutrons  +  barium – 140  +  _______.

2.  The half-life of 3 H is 12.5 years.  A radioactive sample currently has 5.0 mCi of 3 H (Ci = 3.7 * 1010 isotopes disintegrate / second) and originally contained 25 mCi of 3 H.  What is the age of the sample ?  [10 points

 

3.  What does the equation, E = m c2 , mean ?  [5 points]


4.  Sketch the reaction energy profile for an endothermic reaction and label the axis, activation energy of the forward reaction, activation energy of the backward reaction, and the change in enthalpy.  [10 points]

5.   If  the rate of the combustion of ethane, C2 H6 , dethane/dt, what is __.   [10 points]

Hint:  write the balanced chemical equation of this reaction: 

a.   dO2/dt

 

b.  dH2O/dt

6.  For the following hypothetical reaction:  A  -->  B, what is the order of the reaction shown in the below graphs ?  The value of the rate constants are not the same.  Justify your answer.  [10 points]

graph 1

 

graph 2

 

graph 3

 

7.   For the reaction:  N2   + 3 H2   -->  2 NH3 , determine the rate law based on the following (hypothetical) experimental data (include the value & units for the rate constant).  [15 points]



Expt

[N2 ]  (mM)

[H2 ]  (mM)

dH2/dt

1

1.0

1.0

4.74 * 10 -4

2

1.0

4.0

9.48 * 10 -4

3

2.0

9.0

28.44 * 10 -4

8.  Describe the algebraic and graphical methods to determine the activation energy of a chemical reaction; include its basis (need not derive, but show setup and final outcome).  [10 points]

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Nuclear chem. & kinetics  retest            [85 points]                Honors chemistry

 

1.  Write the nuclear equation for  __ / fill-in the blank.   [15 points]

a.  beta decay of  17 O:  ______________________________

b.  fusion involving 7 Li &  17 O:  __________________________

c.  6 Li  +  18 O  -->   11 B  +   _____;   type of nuclear reaction =  ____________

d.   235 Th   -->   90 Sr  +  ____;  type of nuclear reaction = ______________

e.  gamma decay of 24 Na:  _______________________

 

2.  It take 5.0 years for a (hypothetical ?) radioactive isotope to decay from 25 mg to 21 mg.  [10 points]

a.  what is its decay constant ?

b.  how much time would it take for this isotope to decay from 25 mg to 12.5 mg ?


3.  A radioactive isotope has a half-life of 15 years.  How much time would it take a 150 mg sample to become  a 18.75 mg sample ?   [5 points]

 

4.  A chemical reaction generates 55 kJ / mol of heat and the activation energy of the forward reaction is 25 kJ / mole; what is the activation energy of the backward reaction ?   sketch the reaction energy profile of this reaction and label the axis and the preceding energy terms on the graph.   [10 points]

 

5.  Describe how to differentiate between a 0th, 1st, and 2nd order reaction with a single reactant using graphical analysis.  [15 points]


6.   For the reaction:  N2   + 3 H2   -->  2 NH3 , determine the rate law based on the following (hypothetical) experimental data (include the value & units for the rate constant) and determine the reaction rate in expt 4.
[20 points]


Expt

[N2 ]  (mM)

[H2 ]  (mM)

dH2/dt

1

2.0

2.0

4.74 * 10 -4

2

2.0

8.0

9.48 * 10 -4

3

4.0

18.0

28.44 * 10 -4

4

1.0

16.0

        ?

7. catalyst.   [10 points]

a.  what is a catalyst ?   [4 points]

b.  how does a catalyst produce its effect ?  refer to the reaction energy profile, the Arrenhius equation, and the rate law in your response.  [6 points]