Name:  _____________________                              date:  __________________               period: _______

Ch. 17 & 25  kinetics & nuclear chem             test                  70 points                      honors chemistry

In problems involving any calculation, 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.

1. Curie (Ci) is a unit of radioactivity and has a value of 3.7 * 10 10 radioactive isotopes disintegrates per second.  A hypothetical radioactive isotope takes 12.5 years to decay to 5.0 mCi from 25.0 mCi.  A sample of this radioactive isotope had 125 mCi and currently has 35 mCi; what is the “age” of the sample ?  [10 points]

2. Fill-in the below table in regards to the reaction:  C4H10  +  O2  -->  CO2  +  H2O  [10 points]

Rate (mM / sec)

Δ [O2]/Δt  (mM / sec)

Δ [CO2]/Δt  (mM / sec)

8.0

 

 

 

 

32.0



3.  238U undergoes alpha decay to form 234Th and 238U has a half-life of 4.5 billion years.  A sample currently has 25.0 mg of 238U and 15.0 mg 234Th.  Assuming that the sample originally had no 234Th, what is the “age” of the sample ?   [20 points]

4.  Describe the graphical analysis and its basis to estimate the activation energy of a reaction.  Hint:  don’t use the reaction energy profile.  [10 points]


5. In your recent lab involving the reaction:  Na2S2O3 (aq) + HCl (aq) --> S (s) + SO2 (g) + H2O (l) + NaCl (aq), the following hypothetical data was obtained; determine the value of the exponents in the rate law.  [10 points]

Expt

Volume of HCl (1.0 M; mL)

Volume of Na2S2O3   (0.15 M; mL)

Volume of water (mL)

Time (seconds)

1

0.20

0.20

0.60

70

2

0.80

0.20

0

35

3

0.20

0.40

0.40

35

 6. Fill-in the blank of the below (hypothetical ?) nuclear reactions.  [10 points]

a.  Alpha decay of 135Cs:  _________________________________ 

b.  Positron emission of 26Mg:  ___________________________ 

c.  Neutron +  238U  -->  3 neutrons  +  90Sr  +  ___________ 

d. 11Be  +  27Mg  -->  12C  +   _____   

e. ______   -->  electron  +  15Si