Book cover for Chemistry: The Molecular Nature of Matter

Chemistry: The Molecular Nature of Matter

Neil D. Jespersen, James E. Brady, Alison Hyslop

ISBN #9781118413920

7th Edition

3,064 Questions

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53,557 Students Helped

Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

The chapter on Electrochemistry (Chapter 19) provides an in-depth exploration of how chemical energy is converted to electrical energy in galvanic cells through spontaneous redox reactions, and how external energy can drive nonspontaneous reactions in electrolytic cells. Key topics include cell notation, standard reduction potentials, and the relationships between cell potentials, free energy, and equilibrium constants. The Nernst equation is presented as a powerful tool for analyzing cell behavior under nonstandard conditions. The chapter also emphasizes practical applications such as batteries, electroplating, metal refining, and the stoichiometry of electrolysis, underscoring the importance of ion movement and Faraday's laws in these processes.

Learning Objectives

1

Explain the fundamental principles of electrochemistry behind galvanic (voltaic) and electrolytic cells.

2

Calculate standard cell potentials and relate them to free energy and equilibrium constants.

3

Apply the Nernst equation to determine cell potentials under nonstandard conditions.

4

Analyze the practical applications of electrochemistry including batteries, electroplating, metal refining, and industrial chemical production.

5

Utilize Faraday's laws to understand ion movement and electrode reactions during electrolysis.

Key Concepts

CONCEPT

DEFINITION

Galvanic (Voltaic) Cell

An electrochemical cell that converts chemical energy into electrical energy through a spontaneous redox reaction.

Electrolytic Cell

A cell that uses external electrical energy to drive nonspontaneous redox reactions.

Cell Notation

A shorthand representation of the components and reactions occurring in an electrochemical cell, indicating the anode, cathode, and the electrolyte interfaces.

Standard Reduction Potential

A measure of the tendency of a chemical species to gain electrons, measured under standard conditions (1 M, 1 atm, 25°C).

Nernst Equation

An equation that relates the cell potential to the standard cell potential, temperature, number of electrons transferred, and the reaction quotient, used to calculate potentials under nonstandard conditions.

Faraday’s Laws

Fundamental principles that relate the amount of substance transformed at an electrode during electrolysis to the quantity of electricity passed through the cell.

Example Problems

Example 1

What is a galvanic cell? What is a half-cell?

Example 2

What is the function of a salt bridge?

Example 3

In a copper-silver cell, why must the $\mathrm{Cu}^{2+}$ and $\mathrm{Ag}^{+}$ solutions be kept in separate containers?

Example 4

What is the general name we give to reactions that take place at the anode and those that take place at the cathode in a galvanic cell? What is the sign of the electrical charges on the anode and cathode in a galvanic cell?

Example 5

In a galvanic cell, do electrons travel from anode to cathode, or from cathode to anode? Explain.

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Step-by-Step Explanations

QUESTION

Given the standard reduction potentials of the cathode and anode, how do you calculate the standard cell potential (E°cell)?

STEP-BY-STEP ANSWER:

Step 1: Identify the standard reduction potential (E°) of the cathode where reduction occurs.
Step 2: Identify the standard reduction potential of the anode, then reverse its sign to reflect oxidation.
Step 3: Apply the formula: E°cell = E°(cathode) - E°(anode).
Step 4: Ensure that the calculated E°cell is positive to confirm that the reaction is spontaneous.
Final Answer: The standard cell potential is the difference between the cathode and anode reduction potentials, ensuring the anode potential sign is reversed.

Calculating Standard Cell Potential

QUESTION

How do you determine the cell potential under nonstandard conditions using the Nernst equation?

STEP-BY-STEP ANSWER:

Step 1: Write the balanced redox reaction for the electrochemical cell.
Step 2: Determine the number of electrons (n) transferred in the balanced reaction.
Step 3: Write out the Nernst equation: Ecell = E°cell - (RT/nF) * ln(Q), where R is the gas constant, T is the temperature in Kelvin, n is the electrons transferred, F is Faraday's constant, and Q is the reaction quotient.
Step 4: Substitute the known values and the current concentrations into the equation.
Step 5: Solve for Ecell to find the cell potential under these nonstandard conditions.
Final Answer: The cell potential under nonstandard conditions is calculated by adjusting the standard cell potential based on the reaction quotient and temperature using the Nernst equation.

Applying the Nernst Equation

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Common Mistakes

  • Confusing the roles of the anode and cathode by not reversing the sign of the anode’s potential during calculations.
  • Forgetting to check that the standard cell potential is positive to ensure spontaneity in galvanic cells.
  • Incorrectly setting up the reaction quotient (Q) when applying the Nernst equation for nonstandard conditions.
  • Mixing up the conditions and requirements of galvanic versus electrolytic cells, such as spontaneous vs. nonspontaneous reactions.
  • Overlooking the proper use of Faraday's laws in calculating the amount of substance altered during electrolysis.