CHM3101 Electrochemistry

Which of the following statements accurately describes the difference between galvanic and electrolytic cells?

• The anode is the negative terminal for a Galvanic cell because the anode is the source of the electrons where oxidation occurs.

• The flow of electrons goes from the anode to the cathode for galvanic cells.

• Oxidation occurs at the negative terminal, and reduction occurs at the positive terminal for an electrolytic cell.

Based on Standard Reduction Potential at 25℃ given below, calculate the standard cell potential, E°cell.

 $Mg_{\left(aq\right)}^{2+}+2e^-\rightarrow Mg_{\left(s\right)}$   ; E°= -2.37V
 $Al_{\left(aq\right)}^{3+}+3e^-\rightarrow Al_{\left(s\right)}$      ; E°= -1.66V

• - 0.71V

• - 4.03V

• +0.71V

• +4.03V

Which of the following statements accurately describes the Nernst equation shown below?

• At equilibrium, E_cell calculates to a value of 0 and the battery is considered dead because Q becomes K_eq and K_eq has a value of 0.

• Increasing the concentration of the reactants will increase the value of E_cell.

• This equation is used to figure out the standard cell potential at any concentration, partial pressure or temperature.

• At standard conditions, E_cell = E°_cell because all the concentrations are 1 M at an ambient temperature of 273 K.

What is equilibrium constant, K if E°cell=+0.71V at 298 K.

 $Mg_{\left(aq\right)}^{2+}+2e^-\ \rightarrow Mg_{\left(s\right)}\ \ \ \ \ \left(\times3\right)$  
 $Al_{\left(aq\right)}^{3+}+3e^-\rightarrow Al_{\left(s\right)}\ \ \ (\times2)$  
Overall eq:  $3Mg_{\left(s\right)}+2Al_{\left(aq\right)}^{3+}\rightarrow3Mg_{\left(aq\right)}^{2+}+2Al_{\left(s\right)}$  
(F = 96485 C/ mol  $\overline{e}$  ; R= 8.31 J/(mol.K))

•  $1.212\times10^{72}$ 

•  $-1.212\times10^{72}$  

•  $1.101\times10^{36}$  

•  $-1.101\times10^{36}$  

Are dry cell batteries one example of galvanic cells?

• True

• False

In an electrolyte concentration cell, a half-cell with electrolyte of _________ concentration will be at the __________ side.

To answer this question, you can answer more than one.

• lower, cathode

• lower, anode

• higher, cathode

• higher, anode

To eliminate liquid junction potential is by placing the salt bridge in an electrochemical cell?

• True

• False

Cell potential is proportional to the slope of the Gibbs energy with respect to the extent of the reaction.

• True

• False

E° values are dependent on the stoichiometric coefficients for the half-reaction, and, most importantly, the coefficients used to produce a balanced overall reaction do not affect the value of the cell potential.

• True

• False

Shown below is the schematic diagram of a zinc-carbon dry cell. Is it correct about the following half reactions?

Anode half-reaction: $Zn_{\left(s\right)}→Zn_{\left(aq\right)}^{2+}+2e^-$ 
Cathode half-reaction:  $2MnO_{2\left(s\right)}+2NH_{4\left(aq\right)}^-+2e^-→Mn_2O_{3\left(s\right)}+2NH_{3\left(aq\right)}+H_2O_{\left(l\right)}$  

• No

• Yes