Electrochemistry: Free Energy Change

Determine the oxidation state of S in Na$_2$SO$_4$

Assign oxidation numbers for the species below. Determine which species is the oxidizing agent and which is the reducing agent. Which species is being oxidized? Which species is being reduced?

Cr$^{3+}$ + Pb $\longrightarrow$ Cr + Pb$^{2+}$

Balance the redox reaction below

Sn + Ag$^+$ $\longrightarrow$ Sn${^2+}$ + Ag

The following reaction takes place under acidic conditions. Assign oxidation numbers and balance the oxidation reduction reaction using the half reaction method.

HNO$_3$ + Fe$^{2+}$ $\longrightarrow$ Fe$^{3+}$ + NO$_2$