Question

The equation for the fermentation of glucose to alcohol and carbon dioxide is: $$ \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(a q) \longrightarrow 2 \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(a q)+2 \mathrm{CO}_{2}(g) $$ The enthalpy change for the reaction is \(-67 \mathrm{kJ} .\) Is this reaction exothermic or endothermic? Is energy, in the form of heat, absorbed or evolved as the reaction occurs?

Short answer

The fermentation of glucose to alcohol and carbon dioxide is an exothermic reaction, as the enthalpy change is -67 kJ (negative value). Therefore, energy in the form of heat is evolved, not absorbed, during the reaction.

Step-by-step solution

Understand Exothermic and Endothermic Reactions

Exothermic reactions are chemical reactions that release energy in the form of heat. The enthalpy change for exothermic reactions is negative, as the products have lower energy than the reactants. On the other hand, endothermic reactions are chemical reactions that absorb energy in the form of heat. The enthalpy change for endothermic reactions is positive, as the products have higher energy than the reactants.

Determine if the Reaction is Exothermic or Endothermic

As given, the enthalpy change for the fermentation of glucose to alcohol and carbon dioxide is -67 kJ. Since the enthalpy change is negative, it indicates that the reaction is an exothermic reaction.

Determine if Heat is Absorbed or Evolved

Since the reaction is exothermic, energy in the form of heat is released during the reaction. Hence, heat is evolved as the reaction occurs. To sum up: 1. The fermentation of glucose to alcohol and carbon dioxide is an exothermic reaction, given its negative enthalpy change. 2. Energy in the form of heat is evolved, not absorbed, as the reaction occurs.

Key concepts

Enthalpy Change

When we talk about enthalpy change in a chemical reaction, we're referring to the amount of heat absorbed or released during the process. This concept helps determine whether a reaction is exothermic or endothermic.
- **Exothermic Reactions**: These reactions release heat to the surroundings, resulting in a temperature increase. The enthalpy change in exothermic reactions is always negative, because the products of the reaction have less energy than the reactants. In simple terms, energy is given off. - **Endothermic Reactions**: These reactions absorb heat from the surroundings, causing the surroundings to cool down. The enthalpy change here is positive, as the products have more energy than the reactants. Energy is taken in. Understanding enthalpy change is crucial for knowing how energy flows in a chemical process. In the case of glucose fermentation, with an enthalpy change of -67 kJ, we can definitively say that the reaction is exothermic, as energy is given off as heat.

Fermentation Process

Fermentation is a fascinating process often used in various industries, like winemaking, brewing, and even bread making. It involves the breakdown of glucose (a sugar) by microorganisms in the absence of oxygen, producing alcohol and carbon dioxide.
During fermentation:- **Microorganisms such as yeast**: These are often used because they have the ability to convert glucose into ethanol and carbon dioxide. This process is anaerobic, meaning it doesn’t require oxygen.- **Glucose Breakdown**: As seen in the reaction \( ext{C}_6 ext{H}_{12} ext{O}_6 ightarrow 2 ext{C}_2 ext{H}_5 ext{OH} + 2 ext{CO}_2 \), glucose is converted into ethanol and carbon dioxide. This is the primary reaction in alcohol fermentation.Though it primarily produces alcohol, the process also results in the release of heat energy. This by-product is crucial because it confirms that the fermentation is exothermic in nature. Fermentation is not only significant for producing alcohol but also for its role in energy transfer.

Heat Evolution

In any chemical reaction, heat evolution is a key factor in determining the nature and practical implications of the reaction. When a process is exothermic, like the fermentation of glucose, it evolves heat, meaning energy is released in the form of heat to the surroundings.
- **Significance of Heat in Fermentation**: As energy is released during glucose fermentation, it impacts the environment where the reaction occurs. This can be beneficial or problematic, depending on the context. - **Practical Considerations**: Managing evolved heat is critical in industrial fermentation to ensure that temperatures remain within optimal ranges for microorganisms. An uncontrolled increase in temperature might harm the organisms involved, reducing the efficiency. Recognizing heat evolution as a natural feature of exothermic reactions helps in understanding how these reactions occur and are controlled. Therefore, knowing that heat is evolved in fermentation translates to better energy management and process efficiency in practical applications.