Problem 183 - A Complete Resource Book in Chemistry for JEE Main

Question

In a hydrogen-oxygen fuel cell, combustion of hydrogen occurs to [2004] (a) produce high purity water (b) generate heat (c) remove adsorbed oxygen from electrode surfaces (d) create potential difference between the two electrodes

Step-by-Step Solution

Answer

(d) create potential difference between the two electrodes.

Step 1: Understanding the Concept

A hydrogen-oxygen fuel cell is a device that generates electricity through the chemical reaction between hydrogen and oxygen. The key aspect of its operation is to produce electricity, and any side products are secondary results of the reactions taking place within the cell.

Step 2: Identifying the Reactions

In a hydrogen-oxygen fuel cell, hydrogen gas ( ext{H}_2) is oxidized at the anode to produce protons and electrons. At the cathode, oxygen gas ( ext{O}_2) reacts with the protons and electrons to form water ( ext{H}_2O). The overall reaction can be summarized as: 2 ext{H}_2 + ext{O}_2 ightarrow 2 ext{H}_2 ext{O}.

Step 3: Assessing the Options

- Option (a) suggests the production of high-purity water, which is indeed a by-product of the reaction. - Option (b) mentions generating heat, which occurs but is not the primary purpose. - Option (c) implies removing adsorbed oxygen from electrode surfaces, which is not a main function of the fuel cell. - Option (d) focuses on creating a potential difference between the two electrodes, which is essential for electricity generation in the cell.

Step 4: Final Decision

Given the goal of the hydrogen-oxygen fuel cell, to produce electrical energy by creating a potential difference across the electrodes, option (d) is the primary objective of the fuel cell operation. While high purity water is also produced, the creation of electrical potential is the main purpose.

Key Concepts

Electrochemical Reactions

In a hydrogen-oxygen fuel cell, electrochemical reactions are the driving force behind electricity generation. These reactions occur between hydrogen and oxygen, facilitated by a device called a fuel cell.

The process begins at the anode, where hydrogen gas ( ext{H}_2) is supplied. It splits into protons and electrons, a process called oxidation. This involves the protons passing through an electrolyte, while the electrons are sent through an external circuit to create electricity.

• Anode Reaction: ext{2H}_2 ightarrow ext{4H}^+ + ext{4e}^−
• Cathode Reaction: ext{O}_2 + ext{4H}^+ + ext{4e}^- ightarrow ext{2H}_2 ext{O}

Overall, electrochemical reactions in a fuel cell result in the formation of water, while releasing energy that can be harnessed as a power source.

Electricity Generation

Electricity generation in a hydrogen-oxygen fuel cell occurs through a seamless interaction of chemical and electrical processes. The electrons released during hydrogen oxidation travel through an external electrical circuit, providing power to operate devices such as lights or engines.

This flow of electrons generates electrical emissions that can be employed immediately or stored for future use. Moreover, since the only by-products are water and heat, fuel cells present a cleaner alternative to traditional combustion-based electricity generation methods.

• Electrons from the anode travel through a circuit.
• This powers electrical devices before returning to the cathode.

This cycle of electron flow is sustained continuously as long as fuel is supplied, making it a reliable source of electricity.

Anode and Cathode Reactions

The operation of a hydrogen-oxygen fuel cell is intricately tied to the activities at its two main components: the anode and the cathode.

At the anode, hydrogen molecules are split into protons and electrons. This is the starting point of the energy conversion process in the cell. The electrons released form a stream of electricity that exits the cell, traveling through an external circuit, while protons traverse an electrolyte to reach the cathode.

• Anode: The site of hydrogen oxidation and electron flow initiation.

At the cathode, oxygen reacts with the incoming protons and electrons to form water—a simple yet vital reaction completing the circuit.

• Cathode: The site where oxygen reacts with protons and electrons to produce water.
  This dual-reaction process is essential for sustaining the cycle of electricity generation efficiently.