- This equation was named after a German physicist Walther Nernst.
- The Nernst Equation empowers the assurance of cell potential under non-standard conditions and relates the measured cell potential to the reaction quotient and permits the exact measurement of equilibrium constants.
- Let us consider an electrochemical reaction of the following type:
aA +bB --> cC + dD
- Nernst equation for this can be written as follows:
- In case of daniel cell Nerst equation is as follows:
- The above equation implis that the value of increases with the increase in the concentartion of Cu2+ ion increases and decrease in the concentration Zn2+
- Putting the values of R, F at T= 298 K. the equation becomes
- If the circuit in Daniel cell is closed:
Zn(s) + Cu2+ (aq) →Zn2+ (aq) + Cu(s)
- With time the concentration of Zn2+
- The concentration of Cu2+
- Voltage reading of the cell on the voltmeter decreases.
- After some time there is no alteration in the concentration of Cu2+ and Zn2+ ions and the voltmeter gives zero reading. At this point of time equilibrium has been reach
- The Nernst equation for the reaction is:
At T = 298 K.
The equation can be rewritten as
Calculate the emf of the cell in which the following reaction takes place: Ni(s) + 2Ag+ (0.002 M) → Ni2+ (0.160 M) + 2Ag(s). Given that Eøcell = 1.05 V.
By using Nernst equation
= 1.05 - 0.02955 log 4 × 104
= 1.05 - 0.02955 (log 10000 + log 4)
= 1.05 - 0.02955 (4 + 0.6021)
= 0.914 V