Pb(aq)2+ + 2e- → Pb(s) Ero = - 0.13 V
Sc(aq)3+ + 3e- → Sc(s) Ero = - 2.02 V
a) Write a balanced chemical equation for a spontaneous reaction involving these half reactions.
b) Explain your rationale for the reaction going in this direction.
I'm not sure how to go about this, thank you!
Rose, Amy, please use the same screen name.
To write a balanced chemical equation for a spontaneous reaction involving these half-reactions, we need to ensure that both the reduction and oxidation reactions are balanced.
a) To do this, we start by identifying the half-reactions:
Reduction half-reaction: Pb(aq)2+ + 2e- → Pb(s)
Oxidation half-reaction: Sc(aq)3+ → Sc(s) + 3e-
Now, we need to balance the number of electrons in both half-reactions so that they cancel out. To do this, we multiply the oxidation half-reaction by 2:
2 × (Sc(aq)3+ → Sc(s) + 3e-) → 2Sc(aq)3+ → 2Sc(s) + 6e-
Now, we can add the two balanced half-reactions together:
Pb(aq)2+ + 2e- + 2Sc(aq)3+ → 2Sc(s) + Pb(s) + 6e-
Simplifying this equation gives us the balanced chemical equation for the spontaneous reaction:
2Pb(aq)2+ + 2Sc(aq)3+ → 2Sc(s) + Pb(s)
b) The rationale for this reaction going in the given direction lies in the standard electrode potentials (Ero). The reduction potential (Ero) measures the tendency of a species to gain electrons and can be used to determine the direction of a spontaneous reaction.
In the given half-reactions, we have:
Ero for the reduction half-reaction (Pb2+ + 2e- → Pb) = -0.13 V
Ero for the reduction half-reaction (Sc3+ + 3e- → Sc) = -2.02 V
Since the reduction potential for the oxidation half-reaction is more negative than that of the reduction half-reaction, it means that the Sc3+ ion (oxidation) has a higher tendency to gain electrons, and the Pb2+ ion (reduction) has a lower tendency to gain electrons.
Therefore, in the balanced chemical equation, the Sc3+ ion is oxidized (loses electrons) and the Pb2+ ion is reduced (gains electrons). This direction allows the reaction to proceed spontaneously and is in accordance with the principles of electrochemistry.