Electrochemistry Formulas - Gibbs Free Energy, Equilibrium K, Cell Potential, Nernst Equation

Summary

This video covers essential formulas in electrochemistry, helping students prepare for exams. It explains how to calculate cell potential using standard reduction potentials, as well as the relationship between Gibbs free energy and cell potential. The Nernst equation is explored for both standard and non-standard conditions, and how to calculate the equilibrium constant from cell potential. The video also discusses electroplating, charge, and the connection between electric current, time, and charge. With clear explanations of key concepts and equations, this video is a comprehensive resource for understanding electrochemical calculations.

Takeaways

• 😀 The cell potential is calculated by subtracting the anode's cell potential from the cathode's cell potential.
• 😀 The anode undergoes oxidation, and its standard reduction potential needs to be reversed when calculating cell potential.
• 😀 Reduction occurs at the cathode where electrons are gained, and oxidation occurs at the anode where electrons are lost.
• 😀 The cell potential is positive when the cathode potential is higher than the anode potential.
• 😀 Gibbs free energy (ΔG) can be calculated from the cell potential using the formula: ΔG = -nFE_cell.
• 😀 The number of electrons transferred (n) and Faraday’s constant (F) are key components in calculating ΔG.
• 😀 The Nernst equation accounts for non-standard conditions and temperature variations in calculating the cell potential.
• 😀 The Nernst equation for non-standard conditions is: E = E° - (0.591/n) log Q.
• 😀 The reaction quotient (Q) is calculated similarly to the equilibrium constant and excludes solid reactants/products.
• 😀 Faraday’s constant (F) represents the charge of one mole of electrons, equal to 96,485 Coulombs, and can be used to calculate charge (Q) in electrochemical reactions.

Q & A

What is the formula for calculating cell potential in electrochemistry?

The cell potential is calculated as the difference between the cathode and anode cell potentials: E_cell = E_cathode - E_anode. The anode value is reversed because oxidation occurs at the anode, while reduction occurs at the cathode.

Why is the anode's standard reduction potential reversed when calculating cell potential?

The anode's standard reduction potential is reversed because oxidation occurs at the anode, not reduction. When calculating the cell potential, the oxidation reaction at the anode is considered, requiring the reversal of the standard reduction potential.

How do you calculate the Gibbs free energy using the cell potential?

To calculate the Gibbs free energy (ΔG), use the formula: ΔG = -nFE_cell, where n is the number of moles of electrons, F is Faraday’s constant (96,485 C/mol), and E_cell is the cell potential in volts.

What is the relationship between Gibbs free energy and the equilibrium constant?

The relationship is given by the equation ΔG = -RT ln K, where R is the gas constant (8.31 J/mol·K), T is the temperature in Kelvin, and K is the equilibrium constant. You can also express the cell potential in terms of K using the equation E_cell = RT/nF ln K.

What does the Nernst equation describe, and how is it applied?

The Nernst equation is used to calculate the cell potential under non-standard conditions. The formula is: E = E_standard - (0.0591/n) log Q, where Q is the reaction quotient (products over reactants, excluding solids), n is the number of electrons, and E_standard is the standard cell potential.

What is the difference between the two forms of the Nernst equation?

The first form of the Nernst equation uses a logarithm with base 10 (log Q) and is used for standard temperature conditions. The second form, using natural logarithms (ln Q), applies when the temperature changes, and it incorporates the universal gas constant R and Faraday’s constant F.

What is the significance of the reaction quotient (Q) in electrochemical calculations?

The reaction quotient (Q) represents the ratio of products to reactants at any point in the reaction. It is used in the Nernst equation to adjust the cell potential for non-standard conditions. Q is calculated like the equilibrium constant K, excluding solids and pure liquids.

How is the work done by a charge calculated in electrochemistry?

The work done by a charge is calculated using the formula W = QV, where W is the work in joules, Q is the charge in coulombs, and V is the voltage in volts.

What is the relationship between voltage and electric potential difference?

Voltage is the electric potential difference between two points. It is calculated as the difference in electric potential between those points. For example, if the potential at point A is 25V and at point B is 10V, the voltage (electric potential difference) is 15V.

What is Faraday’s constant, and how is it used in electrochemistry?

Faraday’s constant is 96,485 C/mol, which is the amount of electric charge per mole of electrons. It is used in equations involving electric charge, such as calculating Gibbs free energy (ΔG) and the cell potential in electrochemical reactions.