Question

Based on the sign of the standard cell potential, Eco, classify these reactions as spontaneous or nonspontaneous as written. Assume standard conditions. Spontaneous as written Nonspontaneous as written Au + (aq) + 3 Ag(s) + Au(s) + 3 Ag+ (aq) Ni²+ (aq) +52- (aq) Ni(s) +S(s) Pb2+ (aq) + H, (g) → Pb(s) + 2 H+ (aq) Answer Bank

Answer 1

A redox reaction is spontaneous when the standard cell potential, $E^{0}_{cell}$ of the reaction is Positive.(
Ev> 0
)

And a redox reaction is Non-spontaneuos when the $E^{0}_{cell}$ is Negative.( ​​​​​​)

E < 0

Ecel = Ecathode – Eanode

(1.) For

Ni2+ + S2- + Ni + S

Cathode is Ni and anode is S.  
Ecathode = -0.25V
and
PO Egnede = +0.476V

= -0.25 – 0.476 = -0.726V

So this is a Non-spontaneuos reaction.

(2.) For   
AuP+ + 3 Ag + Au + 3 Ag+
Au - Cathode and Ag - Anode .
cathode = +1.50V
,
Egnede = -1.86V

= 1.50 - -1.86 = 3.36V cell

It is a spontaneous reaction.

(3) . For
Pb2+ + H + Pb + 2H+
Pb is cathode and H2 is anode.  
Ecathode = -0.126V
,
PO Panode = 0.01

E1= -0.126 – 0.000 = -0.126V

It is an Non-spontaneuos reaction.

Spontaneous reaction	Non-spontaneuos reaction
AuP+ + 3 Ag + Au + 3 Ag+	Ni2+ + S2- + Ni + S
	Pb2+ + H + Pb + 2H+