12. [20-Q30] Which of the following is not true for a voltaic cell?
a. $E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$
b. The mass of the anode sometimes decreases, depending on the process.
c. The mass of the cathode sometimes increases, depending on the process.
d. Reduction occurs at the cathode.
e. Reduction occurs at the anode.
13. [20-Q39,40] In the redox reaction between water and sulfur below, the reaction has a
standard cell potential ($E^\circ_{cell}$) of -1.09 V. Calculate the nonstandard cell potential ($E_{cell}$) for
this reaction when hydrogen sulfide gas [H$_2$S] is 0.032 M and [O$_2$] is 0.085 M at 298 K.
a. -1.09 V
b. -1.07 V
c. -1.03 V
d. -0.97 V
e. -0.85 V
2 S (s) + 2 H$_2$O (l) $\rightarrow$ 2 H$_2$S (g) + O$_2$ (g)
