Based on the sign of E°cell, classify these reactions as spontaneous or nonspontaneous as written. Assume standard conditions. Zn^2+ (aq) + Sn(s) --> Zn(s) + Sn^2+(aq) Al^3+ (aq) + 3Na(s) --> Al(s) + 3Na^+ (aq) Ni^2+ (aq) + S^2- (aq) --> Ni(s) + S(s)