Problem 57 - Chemistry The Molecular Science

Question

Describe the principal parts of an \(\mathrm{H}_{2} \mid \mathrm{O}_{2}\) fuel cell. Write a balanced equation for the reaction at the cathode; at the anode. Give the formula of the product of the fuel cell reaction.

Step-by-Step Solution

Answer

Cathode: \( \text{O}_2 + 4 \text{H}^+ + 4e^- \rightarrow 2 \text{H}_2\text{O} \); Anode: \( 2 \text{H}_2 \rightarrow 4 \text{H}^+ + 4e^- \); Product: Water (\( \text{H}_2\text{O} \)).

Step 1: Understand the Fuel Cell Reaction

An H2 | O2 fuel cell is an electrochemical cell that generates electricity by the reaction of hydrogen ( H_2 ) and oxygen ( O_2 ). It operates similarly to a battery, but the reactants are supplied externally.

Step 2: Identify the Anode Reaction

At the anode, hydrogen gas (H_2) is oxidized to produce protons (H^+) and electrons. The half-reaction at the anode is:\[ 2 ext{H}_2 (g) ightarrow 4 ext{H}^+ (aq) + 4e^- \]

Step 3: Identify the Cathode Reaction

At the cathode, oxygen gas (O_2) reacts with the protons and electrons to form water (H_2O). The half-reaction at the cathode is:\[ ext{O}_2 (g) + 4 ext{H}^+ (aq) + 4e^- ightarrow 2 ext{H}_2 ext{O}(l) \]

Step 4: Balance Overall Cell Reaction

Combine the anode and cathode reactions to get the overall reaction:\[ 2 ext{H}_2 (g) + ext{O}_2 (g) ightarrow 2 ext{H}_2 ext{O}(l) \]

Step 5: Identify the Product of the Reaction

The product of the H2 | O2 fuel cell reaction is water (H_2O), as seen from the balanced equation: \( 2 ext{H}_2 (g) + ext{O}_2 (g) ightarrow 2 ext{H}_2 ext{O}(l) \).

Key Concepts

Electrochemical Cells

Electrochemical cells are devices that convert chemical energy into electrical energy through a redox reaction. A common example of such a cell is a fuel cell, like the \(\mathrm{H}_{2} | \mathrm{O}_{2}\) fuel cell. Unlike traditional batteries, which have a set amount of reactant to produce electricity, electrochemical cells can continuously supply electricity as long as fuel—hydrogen and oxygen in this case—is provided externally.

This continuous supply is what sets fuel cells apart, providing efficiency and sustainability. These cells have two main electrodes known as the anode and the cathode. They act as the locations for the oxidation and reduction reactions that drive the production of electricity.

• Anode: Oxidation occurs here, leading to the loss of electrons.
• Cathode: Reduction occurs at the cathode, where electrons are gained.

For fuel cells, this electrochemical conversion is particularly important as it leads to fewer pollutants, making it an environmentally friendly alternative to traditional fossil fuels.

Anode and Cathode Reactions

In a \(\mathrm{H}_{2} | \mathrm{O}_{2}\) fuel cell, specific reactions occur at the anode and the cathode to support the flow of electrons. These reactions transform the chemical energy of the reactants into electrical energy.

**Anode Reaction:** At the anode, hydrogen gas \(\mathrm{H}_{2}\) undergoes oxidation. This means that each molecule of hydrogen loses electrons, resulting in the formation of protons \(\mathrm{H}^{+}\) and electrons \(e^{-}\). The half-reaction for the anode is:\[2\mathrm{H}_2(g) \rightarrow 4\mathrm{H}^+(aq) + 4e^- \]**Cathode Reaction:** Meanwhile, at the cathode, oxygen gas \(\mathrm{O}_{2}\) is reduced. This process involves the oxygen molecules gaining electrons and combining with the protons to produce water \(\mathrm{H}_{2}\mathrm{O}\). The half-reaction for the cathode is:\[\mathrm{O}_2(g) + 4\mathrm{H}^+(aq) + 4e^- \rightarrow 2\mathrm{H}_2\mathrm{O}(l) \]These reactions are vital because they contribute to the overall functioning of the fuel cell, allowing it to generate electricity efficiently.

Balanced Chemical Equations

Balanced chemical equations are essential in understanding the stoichiometry of reactions, which is crucial for fuel cells. In a balanced equation, the number of atoms for each element is equal on both sides of the equation, adhering to the law of conservation of mass.

For the \(\mathrm{H}_{2} | \mathrm{O}_{2}\) fuel cell, the anode and cathode reactions combine to form the overall balanced reaction, describing the single process occurring in the cell. This process is illustrated by:\[2\mathrm{H}_2(g) + \mathrm{O}_2(g) \rightarrow 2\mathrm{H}_2\mathrm{O}(l) \]Here, the coefficients balance the number of hydrogen and oxygen atoms, ensuring that each type of atom is conserved. Furthermore, understanding how these components balance helps in designing and applying fuel cell technology effectively.

• Each molecule of oxygen that reacts requires two molecules of hydrogen to maintain balance.
• The reaction produces water, a benign byproduct, highlighting the eco-friendly advantage of fuel cells.

This balanced equation not only ensures mass balance but is key to calculating and predicting the quantities of reactants and products involved in the reaction, which is especially important for the efficiency and application of fuel cells.