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 the reaction exothermic or endothermic? Is energy, in the form of heat, absorbed or evolved as the reaction occurs?

Enthalpy change, often represented by the symbol \( \Delta H \), plays a crucial role in understanding chemical reactions. It is a measure of the total energy change that occurs during a reaction. In the context of the given exercise, the enthalpy change for the fermentation of glucose is \( -67 \text{ kJ} \), signifying a release of energy to the surroundings.

This value helps us classify the reaction's thermal nature; if \( \Delta H \) is negative, the reaction is exothermic, indicating that it releases heat. Conversely, a positive \( \Delta H \) suggests an endothermic reaction where the system absorbs heat from its surroundings. Most importantly, this concept is key in predicting how temperature influences reaction rates and the feasibility of reactions under different conditions.

Fermentation is a biologically significant process in which molecules such as glucose (C6H12O6) are broken down anaerobically. The equation for the fermentation of glucose provided in the exercise:\[ \mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6}(aq) \longrightarrow 2\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{OH}(aq)+2\mathrm{CO}_{2}(g) \]This process is common in yeast and some types of bacteria, resulting in the production of ethanol (C2H5OH) and carbon dioxide (CO2) as byproducts.

Students need to understand that this type of biological reaction is complex, involving multiple steps and enzymes. The fermentation of glucose is also exothermic, meaning it releases energy, a byproduct crucial for various organisms' survival.

Energy plays a fundamental role in chemical reactions. It’s essential to differentiate between reactions that release energy, such as the fermentation of glucose, from those that require energy to proceed. An exothermic reaction, like our example which has a \( \Delta H \) of \( -67 \text{ kJ} \), will release energy predominantly in the form of heat, making the surroundings warmer.

Understanding this is critical for applications in industrial processes, day-to-day activities such as cooking, and even in the natural world where exothermic reactions can affect environmental conditions. Students can better grasp the enthalpy concept by associating it with familiar experiences, such as the warmth felt during the hardening of setting concrete, which is also an exothermic reaction.