Question

For each reaction listed, determine its standard cell potential (in V) at 25°C and whether the reaction is spontaneous at standard conditions.

(a)

Co²⁺(aq) + Mg(s) → Co(s) + Mg²⁺(aq)

ΔE° = V

(b)

2 Al(s) + 3 Cu²⁺(aq) → 2 Al³⁺(aq) + 3 Cu(s)

ΔE° = V

(c)

Ag(s) + Cu(NO₃)₂(aq) → AgNO₃(aq) + CuNO₃(aq)

ΔE° =

(d)

Ni(s) + Zn(NO₃)₂(aq) → Ni(NO₃)₂(aq) + Zn(s)

ΔE° =

Answer 1

CO+2 +2e------>CO, Eo=-0.29V (1) and Mg+2+2e-----> Mg Eo=-2.37V (2), reversing the second reaction gives

Mg-----> Mg+2 +2e- Eo=2.37V (2A)

addition of 1 and 2A gives CO+2 +Mg--------> Mg+2 +Co Eo= 2.37-0.290=2.08 v

dekta G= -nFE, since E is +ve deltaG is- ve which suggests the reaction is spontaneous

2 Al⁺³ +3e- ----- Al, Eo= -1.66V (1) and Cu⁺² +2e- ------->Cu Eo=0.52V (2)

Eq.1*2 gives 2Al+3 +6e- ------->2Al Eo=-1.66v, reversing it 2Al--------->2Al+3 +6e-       Eo=1.66 (3)

Eq.2*3    gives 3Cu+2 +6e- --------> 3Cu Eo=0.52V   (4)

addition of Eq.3 and Eq.4 gives 2Al+3Cu+2 -------->2Al+3 +3Cu Eo= 1.66+0.52= 2.18 V since E is +ve, delta G is-ve the reaction is feasible

3.The ionic equation for the given equation is

2Ag(s) + Cu²+(aq) ---->Cu(s) + 2Ag⁺(aq)

Ag+ +e- ----->Ag , Eo= 0.80V   reversing it gives Ag-----> Ag+ +e- Eo=-0.80V (1)

Cu+2+2e- ---->Cu Eo= 0.34V (2)

multiplying Eq.1 wuth 2 and addition gives 2Ag+Cu+2 -------->2Ag+ +Cu Eo= -0.46V, sicne Eo is -ve and deltaG is +ve the reaction is not spontaneous

4. The ionic reaction is Ni+ Zn+2--------> Zn+Ni+2

Ni -----------> Ni+2 +2e- Eo= -0.25V (1)and Zn+2 +2e---->Zn Eo= -0.76V (2)

addition of Eq.1 and 2 gives Ni+ Zn+2 --------Ni+2 +Zn Eo=-1.01V Since Eo is -ve deltaG is+ve. So the reaction is not spontaneous