The following reaction is spontaneous as written when the components are in their standard states:

3 Zn(s) +2 Cr3+(aq) →3 Zn2+(aq) +2 Cr(s)
If the [Zn2+] is 4 molL−1, determine the value of [Cr3+] below which the reaction will be spontaneous in the opposite direction.

Explanation:

We must use the Nernst equation

E_{\text{cell}} = E_{\text{cell}}^{\circ} - \dfrac{RT}{zF}\ln Q

We want Ecell < 0 for a reverse reaction, so assume it is 0.

Step 1. Calculate E°cell

Anode:     3Zn ⟶ 3Zn²⁺(4 mol·L⁻¹) + 6e⁻;                              E° = +0.7618 V

Cathode: 2Cr³⁺ (x mol·L⁻¹) + 6e⁻ ⟶ 2Cr;                               E° = -0.744   V

Overall:   3Zn + 2Cr³⁺(x mol·L⁻¹) ⟶ 3Zn²⁺(4 mol·L⁻¹) + 2Cr;  E° = +0.018   V

Step 2. Calculate Q

3. Calculate [Cr³⁺]

answer: the rate of diffusion increases with increase in temperature.

increase in temperature, increases the molecular/particles speed (kinetic energy. diffusion means movement of particles through the material.

generally, the heavier the particle the more it interacts with the environment and more the temperature matters. so higher temperature results in higher diffusion.

3

explanation: