Question

Predict whether the following reactions are spontaneous.

1. Pd(aq)2+H2g--------->Pd(s)+2H(aq+) Pd(aq2+) +2e- ----------> Pd(s)
E° 0.987 v
2. Sn(aq4+)+H2(g)--------->Sn(aq2+)+2H+ Sn(aq4+)+2e--------->Sn(aq)2+
E°0.154V
3. Ni(aq2+)+H2(g)--------->Ni(s)+2H(aq+) Ni(aq2+) +2e---------->Ni(s)
E° -0.250 V
4. Cd(aq2+)+H2(g--------> Cds)+2H(aq)+ Cd(aq)2 + +2e -------->
Cd(s) E°-0.403 v
From your answers, decide which of the above metals could be reduced by hydrogen

Answer 1

1. spontaneous

2. spontaneous

3. Not Spontaneous

4. Not Spontaneous

Palladium and Sn^4+ can be reduced by hydrogen.

Step-by-step explanation:

If we look at the electrochemical systems represented above, we will notice that in the first two cells, the metal should be reduced looking at the positive electrode potential of the process. This means that hydrogen can reduce the both metals. Electrons flow from the H2(g)/H^+(aq) half cell to the metal/metal ion half cell.

Similarly, when the standard electrode potential is negative, electrons flow from the metal/metal ion electrode to the hydrogen electrode.

Based on the reaction equations, a process is spontaneous if it gives a positive E°cell hence the answers above.