Name ________________________________________________________________________________
AP Chemistry Ch 18/19 Review
1) How many electrons are transferred in the reaction represented by the following balanced equation?
2 MnO
4
(aq) + 10 Br (aq) + 16 H + (aq)  2 Mn 2+ (aq) + 5 Br
2
(aq) + 8 H
2
O(l)
10 electrons are transferred
2) Write the line notation for each of the following galvanic cells. Then, calculate the ξ° of each. a. 2 Na(s) + Cu 2+ (aq) → 2 Na + (aq) + Cu(s) Na(s) | Na + (aq) || Cu 2+ (aq) | Cu(s)
ξ° = .34-(-2.71) = 3.05 V b. 2 Cl (aq) + Au 3+ (aq)  Cl
2
(g) + Au(s)
ξ° = 1.50 – 1.36 = .14 V
Pt(s) | Cl
2
(g) | Cl (aq) || Au 3+ (aq) | Au(s)
3) Which of the following would be the best reducing agent? K + Au 3+ F
2
ClO
2
Pb 2+ Cr
4) Which of the following would be the best oxidizing agent? K + Au 3+ F
2
ClO
2
Pb 2+ Cr
5) Which of the following can be spontaneously reduced by Cl ? K + Au 3+ F
2
ClO
2
Pb 2+ Cr

6) Zn + Br
2
 Zn 2+ + Br a. Write the two half-reactions for this reaction. i. Anode: Zn  Zn 2+ + 2 e - ii. Cathode: Br
2
+ 2 e  2 Br -
ξ° = -.76 V
ξ° = 1.09 V
7) Write the fully balanced redox reaction. Zn + Br
2
 Zn 2+ a. How many electrons are transferred in this reaction?
+ 2 Br -
2 e b. Calculate ξ° for this reaction.
ξ° = 1.09 – (-.76) = 1.85 V c. Is this reaction spontaneous? Why or why not? Yes, ξ° > 0 d. Calculate ΔG° at 25°C for this reaction.
ΔG° = -nFξ° = -(2)(96485)(1.85) = -356994.5 J = -357 kJ e. If you add a few grams of zinc nitrate to the anode, will the measured voltage increase or decrease?
This would increase the concentration of Zn 2+ in the solution. Since Zn 2+ is a product, equilibrium will be driven to the reactant’s side, and the voltage will decrease.
8) Na + + Fe  Na + Fe 3+ a. Write the two half-reactions for this reaction. i. Anode: Fe  Fe 3+ + 3 e ξ° = - .036 V ii. Cathode: Na + + e  Na ξ° = -2.71 V
You might be tempted to flip the sign on the sodium half-reaction —but be careful, it’s taking place at the cathode in this reaction.
9) Write the fully balanced redox reaction. 3 Na + + Fe  3 Na + Fe 3+ a. How many electrons are transferred in this reaction? 3 e b. Calculate ξ° for this reaction.
ξ° = -2.71 – (-.036) = -2.674 V c. Is this reaction spontaneous? Why or why not? No, ξ° < 0 d. Calculate ΔG° at 25°C for this reaction.
ΔG° = -nFξ° = -(3)(96485)(-2.674) = 774003 J = 774 kJ e. Would this type of reaction take place in an electrolytic cell or a galvanic cell? Explain why.
Electrolytic; this reaction would require an electric current to proceed as written; in this case, electrical current drives a chemical reaction that is normally nonspontaneous

10) An electric current of 20.00 A is passed through an aqueous solution of MnCl
2
. How long will it take to plate out 80.0 g of manganese?
Mn 2+ + 2 e  Mn
80.0 g Mn 1 mole Mn 2 moles e 96485 C
54.938 g Mn 1 mole Mn 1 mole e -
1 sec__
20.00 C
= 14050 seconds
It would take 14050 seconds, or 234 minutes, or 3.9 hours for 80.0 g of manganese to plate out using this current.
11) Describe the types of atoms that tend to undergo each type of nuclear decay. a. Alpha production: common in heavy elements b. Beta production: changes a neutron to a proton ; occurs when the proton:neutron ratio is too low c. Positron production: changes a proton to a neutron ; occurs when the proton:neutron ratio is too high d. Gamma production: releases energy
12) Know how to balance nuclear reactions. Also know the difference between decay and bombardment.
Lol guys you got this
13) Know what half-life is, how to calculate it, how to use it to calculate the amount of a sample that remains after a specific amount of time
Amount left = (original amount)(.5) #half-lives
The book’s way: Decay constant = k = ln(2)/t
1/2
N/No = e -kt