Problem 117 - Chemistry

Question

Producer gas (carbon monoxide) is prepared by passing air over red-hot coke: \(\mathrm{C}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}(g)\) Water gas (a mixture of carbon monoxide and hydrogen) is prepared by passing steam over red-hot coke: \(\mathrm{C}(s)+\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{CO}(g)+\mathrm{H}_{2}(g)\) For many years, both producer gas and water gas were used as fuels in industry and for domestic cooking. The large-scale preparation of these gases was carried out alternately; that is, first producer gas, then water gas, and so on. Using thermochemical reasoning, explain why this procedure was chosen.

Step-by-Step Solution

Answer

Alternating reactions exploit exothermic heat to drive endothermic processes efficiently.

Step 1: Analyze Reactions for Heat Exchange

Examine the chemical reactions given:1. Producer Gas: \(\mathrm{C}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}(g)\)2. Water Gas: \(\mathrm{C}(s)+\mathrm{H}_{2} \mathrm{O}(g) \rightarrow \mathrm{CO}(g)+\mathrm{H}_{2}(g)\)The producer gas reaction involves combustion, which typically releases heat, indicating it is an exothermic reaction. The water gas reaction involves gasification, which is endothermic, requiring heat to proceed.

Step 2: Determine Heat Roles in Interchange

Realizing that the reaction forming producer gas releases heat, this exothermic reaction can help maintain the temperature of the coke bed. On the other hand, the endothermic reaction forming water gas can utilize the residual heat retained in the coke from the producer gas reaction, minimizing additional energy input to sustain the high temperatures required.

Step 3: Evaluate Industrial Efficiency

By alternating the reactions, the process takes advantage of the heat generated from the exothermic reaction to supply the energy needed for the endothermic reaction. This cycling reduces the overall energy cost, making the process more efficient for large-scale operations, and thus was preferred in industrial applications.

Key Concepts

Exothermic Reactions

Exothermic reactions are fascinating chemical processes where energy is released to the surroundings, usually in the form of heat. This occurs when the energy required to break the bonds in the reactants is less than the energy released when new bonds form in the products.

In the context of the producer gas reaction involving carbon and oxygen \( \mathrm{C}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}(g) \), the process is exothermic. This means that the reaction releases heat as it proceeds. The release of heat helps maintain other processes requiring heat, like the following endothermic reaction. The heat from the exothermic reaction helps balance and sustain the energy requirements of the subsequent steps in industrial applications.

• Energy in exothermic reactions is often released as heat.
• These reactions can help initiate or maintain other reactions through heat transfer.
• Exothermic reactions prove cost-effective in industrial processes by reducing external energy requirements.

Understanding how exothermic reactions work allows us to harness them for practical purposes, like fuel production in the chemical industry.

Endothermic Reactions

Endothermic reactions require an input of energy to proceed. Unlike exothermic reactions, they absorb heat from their surroundings. This is because the energy needed to break the bonds in the reactants is greater than the energy released during the formation of the product bonds.

Taking the water gas reaction as an example\( \mathrm{C}(s)+\mathrm{H}_{2} \mathrm{O}(g) \rightarrow \mathrm{CO}(g)+\mathrm{H}_{2}(g) \), it is an endothermic process. This reaction typically requires heat input to reach the necessary temperatures for gasification. However, when conducted after an exothermic reaction, much of the needed heat is already available.

• Endothermic reactions absorb heat, requiring a consistent energy source.
• They are used in industrial processes where heat can be strategically provided or conserved.
• Alternating with exothermic reactions optimizes energy use and process efficiency.

In industries, strategic use of endothermic reactions can lead to energy savings and optimized resource utilization.

Heat Exchange in Reactions

Heat exchange refers to the transfer of heat between different components in a chemical process. It plays a critical role in the efficiency and feasibility of industrial chemical reactions.

In the production of water gas and producer gas, heat exchange allows the energy from exothermic processes to be used by subsequent endothermic reactions.
This exchange minimizes the need for external heating and helps maintain the operational temperatures required for continuous chemical reactions, making large-scale processes more viable.

• Heat exchange maximizes energy efficiency by utilizing the heat from one reaction for another.
• This integration reduces the need for external energy sources.
• Effective heat management is crucial for sustainable and cost-effective industrial practices.

Employing strategies that leverage heat exchange can significantly enhance the economical and environmental sustainability of industrial systems.