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Nernst Equation Calculator

Select the parameter from the list and provide all other required ones to calculate the results through this calculator using Nernst equation.

mV

V

mV

V

°C

°F

K

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Nernst Equation Calculator

An online Nernst equation calculator can calculate the equilibrium potential for an ion based on its concentration and charge. The standard cell potential for an electrochemical cell is determined by the difference between the two half-cell reduction potentials. A positive cell potential indicates a spontaneous reaction. This calculator provides detailed information on the Nernst equation, reduction potential, and equilibrium potential calculations.

What is Nernst Equation?

The Nernst equation relates the electrochemical cell potential to temperature, standard cell potential, and the reaction quotient. It allows calculation of cell potentials under non-standard conditions such as specific pressures, concentrations, and temperatures.

Nernst Equation for Electrode Potential

$$ E_\text{cell} = E^0 - \frac{RT}{nF} \ln Q $$

Where:

  • Q = Reaction Quotient
  • F = Faraday Constant
  • n = Number of electrons transferred in the redox reaction
  • T = Absolute temperature
  • R = Gas constant
  • \( E^0 \) = Standard cell potential
  • \( E_\text{cell} \) = Cell potential under non-standard conditions

For a reduction reaction \( ne^- + M^{n+} \rightarrow nM \), the electrode potential is:

$$ E_\text{red} = E^0_{M^{n+}/M} - \frac{2.303 RT}{nF} \log \frac{1}{[M^{n+}]} $$

Nernst Equilibrium Potential

Examples of equilibrium potential calculations for common ions:

Potassium \(K^+\):

$$ V_K = \frac{RT}{(+1)F} \ln \frac{[K^+]_\text{outside}}{[K^+]_\text{inside}} $$

Chloride \(Cl^-\):

$$ V_{Cl} = \frac{RT}{(-1)F} \ln \frac{[Cl^-]_\text{outside}}{[Cl^-]_\text{inside}} $$

Calcium \(Ca^{2+}\):

$$ V_{Ca} = \frac{RT}{(2)F} \ln \frac{[Ca^{2+}]_\text{outside}}{[Ca^{2+}]_\text{inside}} $$

Nernst Equilibrium Potential Table

Ionic Species Intracellular Concentration Extracellular Concentration Equilibrium Potential
Sodium (Na+) 15 mM 145 mM VNa = +60.60 mV
Potassium (K+) 150 mM 4 mM VK = −96.81 mV
Calcium (Ca2+) 70 nM 2 mM VCa = +137.04 mV
Hydrogen (H+) 63 nM (pH 7.2) 40 nM (pH 7.4) VH = −12.13 mV
Magnesium (Mg2+) 0.5 mM 1 mM VMg = +9.26 mV
Chloride (Cl−) 10 mM 110 mM VCl = −64.05 mV
Bicarbonate (HCO3−) 15 mM 24 mM VHCO3- = −12.55 mV

How to Calculate Equilibrium Potential

Example: Calculate the electrode potential of a 2 M solution at 300 K, with a standard electrode potential of 0.76 V for zinc:

$$ E_{Zn^{2+}/Zn} = 0.76 - \frac{2.303 \times 8.314 \times 300}{2 \times 96500} \log \frac{1}{2} \approx 0.769 \, V $$

Calculate Equilibrium Constant

At equilibrium, \( \Delta G = 0 \), and the Nernst equation becomes:

$$ 0 = E^0_\text{cell} - \frac{RT}{nF} \ln K_c $$

For standard temperature (298 K) and base 10 logarithms:

$$ E^0_\text{cell} = \frac{0.059 \, \text{V}}{n} \log K_c $$

Example: Silver-Copper Cell

Given: \(E^0(Cu^{2+}/Cu) = 0.34 V\), \(E^0(Ag^+/Ag) = 0.8 V\), measured cell potential 0.422 V, [Cu2+] = 0.1 M.

Using the Nernst equation:

$$ 0.422 = 0.46 - 0.0295 \log \frac{0.1}{[Ag^+]^2} \implies [Ag^+] \approx 0.072 \, M $$

Reducing Power of Metals

Given standard electrode potentials:

  • Zn: −0.76 V
  • Ca: −2.87 V
  • Ni: −0.25 V
  • Mg: −2.36 V

Decreasing order of reducing power: Ca > Mg > Zn > Ni

Nernst Equation Limitations

  • Valid for dilute solutions; at high concentrations, ion activities must be used.
  • Valid only when there is no net current through the electrode.
  • At very low ion concentrations, potentials may become physically meaningless.

How Does the Nernst Equation Calculator Work?

Input:

  • Select the variable to calculate.
  • Enter known values and select units.
  • Click Calculate.

Output:

  • Cell potential (\(E_\text{cell}\))
  • Standard cell potential (\(E^0\))
  • Gas constant (R)
  • Temperature (T)
  • Number of electrons (n)
  • Faraday constant (F)
  • Reaction quotient (Q)

FAQs

Applications of the Nernst Equation

  • Oxidation/reduction potential under any conditions
  • Electromotive force (EMF) of a cell
  • Standard electrode potential
  • Concentration of unknown ions

Effect of Temperature

Increasing temperature generally decreases the cell potential if other parameters remain constant.

Nernst Equation at 25°C

At 298 K, simplified form:

$$ E = E^0 - \frac{0.0592}{n} \log_{10} Q $$

Conclusion

This online Nernst equation calculator allows quick calculation of reduction potentials, EMF, and equilibrium potentials for electrochemical cells, aiding scientists and engineers in battery design and energy optimization.

References

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