CTU Radioactive Decay Exam – Order the species below in increasing

What is a cation afraid of? A dogion!

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Read all questions carefully and be sure to answer the question that is asked. To receive full credit, show ALL work (including units). Provide numeric answers with proper significant figures and correct units. Answers without units will NOT receive credit. Limit explanations to two sentences (anything beyond two sentences will NOT be graded). Please write dark so that the scanned exam is legible.

1.            (10 pts) Order the species below in increasing strength as an oxidizing agent.

Na+, Fe3+, Cl2 (g), Zn2+, H2 (g)

2.            (12 pts) For the below reaction, circle the true statement.

3 Cu 2+ (aq) + 2 Al (s) ? 3 Cu (s) + 2 Al 3+ (aq)

a.            Which electrode is the cathode?

i.              Al

ii.             Cu

b.            Which electrode is the anode?

i.              Al

ii.             Cu

c.             What is the reducing agent?

i.              Cu 2+

ii.             Al

d.            What is the oxidizing agent?

i.              Cu 2+

ii.             Al

e.            Which electrode will gain mass?

i.              Al

ii.             Cu

f.             Which electrode will lose mass?

i.              Al

ii.             Cu

3.            (6 pts) When 235Th experiences radioactive decay, the product is235Pa. Write the

90           91

chemical equation for the decay.

 4.           (8 pts) Consider the melting of solid butane to liquid butane at -100.°C (above the normal melting point). If butane has a ΔHfusion=5.0 kJ/mol, calculate the entropy change (in J/K) when 3.45 g of butane (molar mass= 58.0 g/mol) melts at -100.°C.

5.            A reaction has a ΔH°= 204.6 kJ and a ΔS°= -19.5 J/K.

a.            (6 pts) Given the sign and magnitude of ΔH and ΔS, will the reaction be spontaneous at all temperatures, nonspontaneous at all temperatures? Briefly explain your reasoning.

b.            (6 pts) Calculate the standard free energy change for the reaction at 298 K.

c.             (2 pts) Is the reaction spontaneous or nonspontaneous at 298 K?

6.            The below reaction has a ΔG°= + 56.0 kJ/mol at 298 K.

N2 (g) + O2 (g) <-> 2 NO (g)

a.            (6 pts) What is the equilibrium constant for this reaction?

 b.           (8 pts) If [N2] = 0.375 M, [O2] = 0.689 M, and [NO]= 0.758, what will the actual free energy change be for the reaction if it occurs at 298 K?

c.             (2 pts) What is ΔG at equilibrium?

7.            The below is an unbalanced redox reaction in acidic conditions.

Mn (s) + NO –     ? NO (g) + Mn2+ (aq)

a.            (10 pts) Balance the equation.

b.            (4 pts) How many electrons are transferred in the balanced reaction?

c.             (4 pts) Using the standard reduction potential table and E°Red Mn2+/Mn= – 1.18 V, calculate the standard emf for the reaction.

 d.           (8 pts) If concentrations in solution are 1.25 M NO3-, 0.250 M Mn2+, 0.050 M H+ and 1.25 M NO, what will the actual emf be?

e.            (6 pts) What is the actual ΔG be given the emf calculated in part d?

f.             (2 pts) Is the reaction spontaneous or nonspontaneous under these conditions?