Question 16.9: Predicting Spontaneous Redox Reactions Determine whether eac......
Predicting Spontaneous Redox Reactions
Determine whether each redox reaction is spontaneous.
(a) \mathrm{Fe}(s)\,+\,\mathrm{Mg}^{2+}(a q)\,\longrightarrow\,\mathrm{Fe}^{2+}(a q)\,+\,\mathrm{Mg}(s)
(b) \mathrm{Fe}(s)\,+\,\mathrm{Pb}^{2\,+}(a q)\,\longrightarrow\,\mathrm{Fe}^{2\,+}(a q)\,+\,\mathrm{Pb}(s)
(a) \mathrm{Fe}(s)+\mathrm{Mg}^{2+}(a q)\longrightarrow\mathrm{Fe}^{2+}(a q)+\mathrm{Mg}(s)
This reaction involves the oxidation of Fe:
\mathrm{Fe}(s)\ \longrightarrow\,\mathrm{Fe}^{2+}(a q)+2\mathrm{e}^{-}
with the reverse of a half-reaction above it in the activity series:
\mathrm{Mg}^{2+}(a q)+2\mathrm{e}^{-}\longrightarrow\mathrm{Mg}(s)
Therefore, the reaction is not spontaneous.
(b) \mathrm{Fe}(s)+\mathrm{Pb}^{2+}(a q)\longrightarrow\mathrm{Fe}^{2+}(a q)+\mathrm{Pb}(s)
This reaction involves the oxidation of Fe:
\mathrm{Fe}(s)\ \longrightarrow\,\mathrm{Fe}^{2+}(a q)+2\mathrm{e}^{-}
with the reverse of a half-reaction below it in the activity series:
\mathrm{P b}^{2+}(a q)+2\mathrm{e}^{-}\longrightarrow\mathrm{P b}(s)
Therefore, the reaction is spontaneous.