Download AP Chem – Ch16,17 FRQ Reviews Ch16 FRQ Review 1. Use

AP Chem – Ch16,17 FRQ Reviews
Ch16 FRQ Review
1. Use principles of thermodynamics to answer the following questions.
(a) The gas N2O4 decomposes to form the gas NO2 according to the equation:
(i) Predict the sign of ∆H° for the reaction. Justify your answer.
(ii) Predict the sign of ∆S° for the reaction. Justify your answer.
(b) One of the diagrams best represents the relationship between ∆G° and temperature for the reaction
given in part (a). Assume that ∆H° and ∆S° are independent of temperature.
Draw a circle around the correct graph.
Explain why you chose that graph in terms of the relationship ∆G° = ∆H° - T∆S°.
(c) A reaction mixture of N2O4 and NO2 is at equilibrium.
N2O4(g)
2NO2(g)
Heat is added to the mixture while the mixture is maintained at constant pressure
(i) Explain why the concentration of N2O4 decreases.
(ii) The value of Keq at 25°C is 5.0 x 10-3.
Will the value of Keq at 100°C be greater than, less than, or equal to this value?
(d) Using the value of Keq at 25°C given in part (c-ii), predict whether the value of ∆H° is expected to be
greater than, less than, or equal to the value of T∆S°. Explain.
Ch17 FRQ Review
1. An external direct-current power supply is connected to two platinum
electrodes immersed in a beaker containing 1.0 M CuSO₄(ag) at 25°C,
as shown in the diagram. As the cell operates, copper metal is deposited
onto one electrode and O₂(g) is produced as the other electrode.
The two reduction half-reactions for the overall reaction that occurs
in the cell are show in the table below.
Half-reaction
E° (V)
O₂(g) + 4 H⁺(ag) + 4 e⁻ → 2 H₂O(l) +1.23
+0.34
Cu²⁺(ag) + 2 e⁻ → Cu(s)
(a) On the diagram, indicate the direction of electron flow in the wire.
(b) Write a balanced net ionic equation for the electrolysis reaction that occurs in the cell.
(c) Predict the algebraic sign of ∆G° for the reaction. Justify your answer.
An electric current of 1.50 Amps passes through the cell for 40.0 minutes.
(d) Calculate the mass, in grams, of the Cu(s) that is deposited on the electrode.
(e)Calculate the dry volume, in liters measured at 25°C and 1.16 atm, of the O₂(g) that is produced.
Ch17 FRQ Review from 2015 AP Test
1. Metal-air cells a relatively new type of portable energy source consisting
of a metal anode, an alkaline electrolyte paste that contains water,
and a porous cathode membrane that lets in oxygen from the air.
A schematic of the cell is shown. Reduction potentials for the cathode
and three possible metal anodes are given in the table below.
Half Reaction
E at pH 11 and 298 K (V)
O2(g) + 2 H2O (l) + 4 e- → 4 OH-(aq)
+0.34
ZnO(s) + H2O(l) + 2 e → Zn(s)+ 2 OH (aq)
-1.31
Na2O(s) + H2O(l) + 2 e- → 2 Na(s) + 2 OH-(aq)
-1.60
CaO(s) + H2O(l) + 2 e → Ca(s) + 2 OH (aq)
-2.78
(a) Early forms of metal-air cells used zinc as the anode.
Zinc oxide is produced as the cell operates according to the overall
equation below.
2Zn(s) + O2(g) → 2ZnO(s)
(i) Using the data in the table above, calculate the cell potential
for the zinc-air cell.
(ii) The electrolyte paste contains OH- ions. On the diagram of the cell above,
draw an arrow to indicate the direction of migration of OH- ions through the electrolyte as the cell operates.
(b) A fresh zinc-air cell is weighted on an analytical balance before being placed in a hearing aid for use.
(i) As the cell operates, does the mass of the cell increase, decrease or remains the same?
(ii) Justify your answer to part (b-i) in terms of the equation for the overall cell reaction.
(c) The zinc-air cell is taken to the top of mountain where the air pressure is lower.
(i) Will the cell potential be higher, lower, or the same as the cell potential at the lower elevation?
(ii) Justify your answer to part (c-i) based on the equation for the overall cell reaction and the information above.
(d) Metal-air cells need to be lightweight for many applications. In order to transfer more electrons with a smaller mass,
Na and Ca are investigated as potential anodes. A 1.0g anode of which of these metals would transfer more
electrons, assuming that the anode is totally consumed during the lifetime of a cell?
Justify your answer with calculations.
(e) The only common oxide of zinc has the formula ZnO.
(i) Write the electron configuration for a Zn atom in the ground state.
(ii) From which sublevel are electrons removed when a Zn atom in the ground state is oxidized.
Ch16 FRQ Review from 2015 AP Test
1. Answer the following questions about the solubility of Ca(OH)2 (Ksp = 1.3 x 10-6).
(a) Write a balanced chemical equation for the dissolution of Ca(OH)2(s) in pure water.
(b) Calculate the molar solubility of Ca(OH)2 in 0.10 M Ca(OH3)2.
(c) In the box below, complete a particle representation diagram that includes four water molecules
with proper orientation around the Ca2+ ion.
Represent water molecules as