UK K12 GCSE/A-Level: Year 13 A-Level Upper Sixth Chemistry - Electrochemistry, Electrode Potentials, Fuel Cells

Learning Objectives

By the end of this topic, students will be able to:

• Explain the concept of electrode potentials and their significance in electrochemistry
• Calculate the standard electrode potential of a cell using the Nernst equation
• Describe the operation of a fuel cell and its applications
• Evaluate the advantages and limitations of fuel cells as an energy source
• Apply the principles of electrode potentials to predict the spontaneity of electrochemical reactions

Core Concepts

Electrode potentials are a measure of the tendency of a metal to lose or gain electrons. The standard electrode potential (E°) is a measure of the potential difference between a metal and its ions in a solution. It is measured in volts (V) and is a fundamental concept in electrochemistry.

The Nernst equation is used to calculate the standard electrode potential of a cell:

E° = E°(cathode) - E°(anode)

where E°(cathode) and E°(anode) are the standard electrode potentials of the cathode and anode, respectively.

A fuel cell is an electrochemical cell that converts chemical energy into electrical energy. It consists of two electrodes, an anode and a cathode, separated by an electrolyte. The anode is typically made of a fuel such as hydrogen or methane, while the cathode is made of an oxidizing agent such as oxygen.

The operation of a fuel cell can be summarized as follows:

• Hydrogen gas is fed to the anode, where it is oxidized to form protons and electrons.
• The protons pass through the electrolyte to the cathode, where they react with oxygen to form water.
• The electrons flow through an external circuit, generating an electric current.

Worked Examples

Example 1

Calculate the standard electrode potential of a cell consisting of a zinc anode and a copper cathode in a solution of zinc sulfate and copper sulfate.

E°(Zn2+/Zn) = -0.76 V E°(Cu2+/Cu) = +0.34 V

Using the Nernst equation, we can calculate the standard electrode potential of the cell:

E° = E°(cathode) - E°(anode) = +0.34 V - (-0.76 V) = +1.10 V

Therefore, the standard electrode potential of the cell is +1.10 V.

Example 2

A fuel cell is used to convert hydrogen gas into electrical energy. The anode is made of platinum, while the cathode is made of oxygen. The standard electrode potential of the anode is -0.83 V, while the standard electrode potential of the cathode is +0.40 V. Calculate the standard electrode potential of the fuel cell.

Using the Nernst equation, we can calculate the standard electrode potential of the fuel cell:

E° = E°(cathode) - E°(anode) = +0.40 V - (-0.83 V) = +1.23 V

Therefore, the standard electrode potential of the fuel cell is +1.23 V.

Common Misconceptions

• Many students mistakenly believe that electrode potentials are a measure of the energy released or absorbed during an electrochemical reaction. In fact, electrode potentials are a measure of the tendency of a metal to lose or gain electrons.
• Some students may confuse the Nernst equation with the equation for the standard free energy change (?G°). While both equations involve the standard electrode potential, the Nernst equation is used to calculate the standard electrode potential of a cell, while the equation for ?G° is used to calculate the standard free energy change of a reaction.
• Fuel cells are often mistakenly believed to be a new and innovative technology. In fact, fuel cells have been in development for over a century and have been used in a variety of applications, including power generation and transportation.

Exam Tips

• Make sure to understand the concept of electrode potentials and how they are used to calculate the standard electrode potential of a cell.
• Be able to apply the Nernst equation to calculate the standard electrode potential of a cell.
• Understand the operation of a fuel cell and its applications.
• Be able to evaluate the advantages and limitations of fuel cells as an energy source.
• Practice calculating the standard electrode potential of a cell using the Nernst equation.

MCQs with Explanations

MCQ 1 [F]

What is the standard electrode potential of a cell consisting of a zinc anode and a copper cathode in a solution of zinc sulfate and copper sulfate?

A) -0.76 V B) +0.34 V C) +1.10 V D) -1.10 V

Correct answer: C) +1.10 V

Why the distractors fail: A) -0.76 V is the standard electrode potential of the zinc anode, while B) +0.34 V is the standard electrode potential of the copper cathode. D) -1.10 V is the opposite of the correct answer.

MCQ 2 [H]

A fuel cell is used to convert hydrogen gas into electrical energy. The anode is made of platinum, while the cathode is made of oxygen. The standard electrode potential of the anode is -0.83 V, while the standard electrode potential of the cathode is +0.40 V. What is the standard electrode potential of the fuel cell?

A) +0.57 V B) +1.23 V C) -0.57 V D) -1.23 V

Correct answer: B) +1.23 V

Why the distractors fail: A) +0.57 V is the difference between the standard electrode potential of the cathode and the anode, while C) -0.57 V is the opposite of the correct answer. D) -1.23 V is the opposite of the correct answer.

MCQ 3 [F]

What is the function of the electrolyte in a fuel cell?

A) To conduct electricity B) To separate the anode and cathode C) To facilitate the reaction between the anode and cathode D) To store energy

Correct answer: C) To facilitate the reaction between the anode and cathode

Why the distractors fail: A) The electrolyte does not conduct electricity, but rather facilitates the reaction between the anode and cathode. B) The electrolyte is not used to separate the anode and cathode, but rather to bring them together. D) The electrolyte does not store energy, but rather facilitates the reaction between the anode and cathode.

MCQ 4 [H]

What is the advantage of using a fuel cell as an energy source?

A) High energy density B) Low energy density C) High efficiency D) Low efficiency

Correct answer: C) High efficiency

Why the distractors fail: A) Fuel cells do not have high energy density, but rather high power density. B) Fuel cells do not have low energy density, but rather high power density. D) Fuel cells do not have low efficiency, but rather high efficiency.

MCQ 5 [F]

What is the byproduct of a fuel cell reaction?

A) Water B) Carbon dioxide C) Hydrogen gas D) Oxygen gas

Correct answer: A) Water

Why the distractors fail: B) Carbon dioxide is not a byproduct of a fuel cell reaction, but rather a byproduct of combustion. C) Hydrogen gas is the fuel used in a fuel cell reaction, not the byproduct. D) Oxygen gas is not a byproduct of a fuel cell reaction, but rather a reactant.

Short-answer questions

Question 1

Explain the concept of electrode potentials and how they are used to calculate the standard electrode potential of a cell.

Question 2

Describe the operation of a fuel cell and its applications.

Question 3

Evaluate the advantages and limitations of fuel cells as an energy source.

Question 4

Calculate the standard electrode potential of a cell consisting of a zinc anode and a copper cathode in a solution of zinc sulfate and copper sulfate.

Question 5

Calculate the standard electrode potential of a fuel cell used to convert hydrogen gas into electrical energy. The anode is made of platinum, while the cathode is made of oxygen. The standard electrode potential of the anode is -0.83 V, while the standard electrode potential of the cathode is +0.40 V.