Electrochemistry Review Quiz MCQ

C) ΔG* < 0 and Keq > 1

2 H202(aq) --> 2H2O(l) + O2(g) E*=0.55V The equation and standard cell potential for the docomposition of H2O2(aq) in acidic solution at 25*C is given above. Reduction half-reactions for the process are listed below. O2(g) + 4H+(aq) + 4e- --> 2H2o(l) E* = 1.23 V O2(g) + 2H+(aq) + 2e- --> H2O2(aq) E* = ? Which of the following is true for the decomposition of H2O2(aq)? A) ΔG* > 0 and Keq > 1 B) ΔG* > 0 and Keq < 1 C) ΔG* < 0 and Keq > 1 D) ΔG* < 0 and Keq < 1

-.74V

A student sets up a galvanic cell at 298 K that has an electrode of Ag(s) immersed in a 1.0 M solution of Ag+(aq) and an electrode of Cr(s) immersed in a 1.0 M solution of Cr3+(aq), as shown in the diagram above. Half-Reaction: 1. Ag+(aq) + e- --> Ag(s) 2. Cr3+(aq) + 3 e- --> Cr(s) E* (V): 1. +0.80 2. ? b) The student adds the missing component to the cell and measures E*cell to be +1.54 V. As the cell operates, Ag+ ions are reduced. Use this information and the information in the table above to do the following. i) Calculate the value of the E* for the half-reaction Cr3+(aq) + 3 e- --> Cr(s)

Anode is losing mass while cathode is gaining mass As the anode goes down so does the voltage The voltage is stops when there is no more anode left

A voltaic cell is running for a certain amount of time what happens to the anode and cathode? What happens to the volts as the cell runs? What happens to the voltage when the anode is gone?

B) 2

Al(s) --> Al3+(aq) + 3e- Zn2+(aq) + 2e- --> Zn(s) The half-reactions for the oxidation reaction between Al(s) and Zn2+(aq) are represented above. Based on the half-reactions, what is the coefficient for Al(s) if the equation for the oxidation-reduction reaction is balanced with the smallest whole-number coefficients? A) 1 B) 2 C) 3 D) 4

D) [Cu2+] = 0.10 M an [Mg2+] = 1.0 M, because Q is smaller than 1, making Ecell decrease.

Cu2+(aq) +Mg(s) --> Cu(s) + Mg2+(aq) E*cell = +2.71V A galvanic cell generates a potential of +2.71 when [Cu2+] = [Mg2+] = 1M based on the chemical reaction represented above. Which of the following provides the best justification that the given conditions can be used to decrease the cell potential (Ecell < +2.71 V)? A) [Cu+2] = [Mg2+] = 0.10 M, because equilibrium is approached at a faster rate, causing a decrease in Ecell. B) [Cu2+] = [Mg2+] = 2.0 M, because equilibrium is approached at a slower rate, causing a decrease in Ecell. C) [Cu2+] = 1.0 M an [Mg2+] = 0.10 M, because Q is smaller than 1, making Ecell decrease. D) [Cu2+] = 0.10 M an [Mg2+] = 1.0 M, because Q is smaller than 1, making Ecell decrease.

A) I = (2 * 0.125 * 96,485 / 3,600) A

CuCl2(aq) --> Cu(s) + Cl2(g) The diagram above shows the apparatus used for the electrolysis of CuCl2(aq) according tot he chemical equation given. Which of the following mathematical expressions can be used to calculate the current required to produce 0.125 mol of Cu(s) in 1 hour? A) I = (2 * 0.125 * 96,485 / 3,600) A B) I = (2 * 0.125 * 96,485 / 1) A C) I = (0.125 * 96,485 / 3,600) A D) I = (0.125 * 96,485 / 1) A

B) E*cell (V) +1.63 ΔG*(kJ/molrxn) -944

Half-Reaction: 1. Mg2+(aq) + 2e- --> Mg(s) 2. Cr3+(aq) + 3e- --> Cr(s) E* (V): 1. -2.37 2. -0.74 Based on the information in the table above, which of the following shows the cell potential and the Gibbs free energy change for the overall reaction that occurs in a standard galvanic cell? A) E*cell (V) +1.63 ΔG*(kJ/molrxn) -157 B) E*cell (V) +1.63 ΔG*(kJ/molrxn) -944 C) E*cell (V) +5.63 ΔG*(kJ/molrxn) -543 D) E*cell (V) +5.63 ΔG*(kJ/molrxn) -3262

D) 2 Ag+(aq) + Ni(s) --> 2Ag(s) + Ni2+(aq)

Ni(s) --> Ni2+(aq) +2e- Ag+(aq) +e- --> Ag(s) Which of the following is the balanced net iconic equation for an oxidation-reduction reaction between Ag+(aq) and Ni(s) based on the half-reactions represented above? A) Ag+(aq) + Ni(s) --> Ag(s) + Ni2+(aq) B) 2 Ag+(aq) + Ni(s) --> Ag(s) + 2 Ni2+(aq) C) Ag+(aq) + 2 Ni(s) --> Ag(s) + 2 Ni2+(aq) D) 2 Ag+(aq) + Ni(s) --> 2 Ag(s) + Ni2+(aq)

C) Mass = (0.80 * 30.0 * 60 * 107.9 / 96,485)g

The diagram above shows the experimental setup used to electroplate a small object. A current of 0.80 ampere is supplied to AgNO3(aq) for 30.0 minutes. Which of the following equations can be used to calculate the approximate mass of Ag(s) deposited on the object? A) Mass = (0.80 * 30.0 * 60 / 96,485 * 107.9)g B) Mass = (0.80 * 30.0 * 60 * 96,585 / 1079)g C) Mass = (0.80 * 30.0 * 60 * 107.9 / 96,485)g D) Mass = (0.80 * 30.0 * 107.9 / 96,485)g

B) Voltage decreases but remains above zero

The spontaneous reaction that occurs when the cell above operates is 2 Ag+ + Cd(s) --> 2 Ag(s) + Cd2+ Which of the above occurs for the following circumstances? A 50-milliliter sample of a 2 molar Cd(NO3)2 solution is added to the left beaker. A) Voltage increases B) Voltage decreases but remains above zero C) Voltage becomes zero and remains at zero D) No change in voltage occurs E) Direction of voltage change cannot be predicted without additional information

D) No change in voltage occurs

The spontaneous reaction that occurs when the cell above operates is 2 Ag+ + Cd(s) --> Ag(s) + Cd2+ Which of the above occurs for the following circumstances? The silver electrode is made larger. A) Voltage increases B) Voltage decreases but remains above zero C) Voltage becomes zero and remains at zero D) No change in voltage occurs E) Direction of voltage change cannot be predicted without additional information

D) E*cell = +0.02 V

The standard reduction potentials for the half-reactions related to the galvanic cell represented above are listed in the table below. Half-reaction: 1. Cr3+(aq) + 3e- --> Cr(s) 2. Zn 2+(aq) + 2e- --> Zn(s) E* (V): 1. -0.74 2. -0.76 Which of the following gives the value of E*cell for the cell? A) E*cell = -1.50 V B) E* cell = -0.80 V C) E*cell = -0.02 V D) E*cell = +0.02 V

Allows positive and negative ions to flow freely from on cell to another to balance out the gaining/losing of electrons

What does the salt bridge do?