Question

Zn²⁺ → Zn ₍ₛ₎ ; E⁰ = -0.76 V
Cu²⁺ → Cu ₍ₛ₎ ; E⁰ = -0.34V
Which of the following is spontaneous?
(a) Zn²⁺ + Cu → Zn + Cu²⁺
(b) Cu²⁺ + Zn →Cu + Zn²⁺
(c) Zn²⁺ + Cu²⁺ → Zn + Cu
(d) None of these

Answer 1

$\huge{\boxed{\mathfrak\pink{\fcolorbox{red}{purple}{Mr\:Awesome}}}}$

❤.option B is correct

Answer 2

From following, spontaneous is :

Given : Zn²⁺ → Zn ₍ₛ₎ ; E⁰ = -0.76 V

Cu²⁺ → Cu ₍ₛ₎ ; E⁰ = -0.34V

• For spontaneous reaction, E⁰ i.e standard electrode potential should be positive for whole reaction.

E°cell (Zn2+/Zn) = -0.76V, E°cell (Cu2+/Cu) = +0.34V

1) Zn²⁺ + Cu → Zn + Cu²⁺

E⁰rxn = -0.76 V - 0.34V = - 1.10V

• Non-feasible

2) Cu²⁺ + Zn →Cu + Zn²⁺

+0.34V - (-0.76 ) = +1.10V

• Hence reaction (b) is spontaneous.