Question

Given the following half-reactions and their standard reduction potentials,

Ni2+ + 2e− Ni E° = -0.25 V
2H+ + 2e− H2 E° = 0.00 V
Ag+ + e− Ag E° = 0.80 V
a spontaneous reaction will occur between:

a. Ni2+ and H2
b. H+ and Ag
c. Ag+ and Ni
d. Ni2+ and Ag+
e. H+ can react spontaneously with any of the species here because its reduction potential is zero

I don't know I think the answer is 3 or 4? Some help? Thank you

Answer 1

The answer is c.
a won't work. Why?
Ni^2+ is -0.25 with
H2 is 0 so Ecell is negative and that isn't spontaneous.

But c will. Why?
Ag^+ is 0.8
Ni to Ni^+ is +0.25
Add and Ecell is + so rxn is spontaneous.

You can go through the others to convince yourself that all are negative.