In photosynthesis, green plants convert carbon dioxide and water into glucose (C6H12O6) according to the following equation: 6 CO2(g) + 6 H2O(l) → C6H12O6(aq) + 6 O2(g) Estimate ∆H for the reaction using bond dissociation energies from Table 7.1. Give your answer in kcal/mol and kJ/mol. (C6H12O6 has five C―C bonds, seven C―H bonds, seven C―O bonds, and five O―H bonds).

Verified step by step guidance

1. Identify the bonds broken in the reactants: 6 CO2 and 6 H2O. Calculate the total energy required to break these bonds using bond dissociation energies.
2. Identify the bonds formed in the products: C6H12O6 and 6 O2. Calculate the total energy released when these bonds are formed using bond dissociation energies.
3. Use the formula for the change in enthalpy (∆H) of the reaction: ∆H = (Total energy of bonds broken) - (Total energy of bonds formed).
4. Convert the calculated ∆H from kcal/mol to kJ/mol using the conversion factor: 1 kcal = 4.184 kJ.
5. Summarize the steps and ensure all calculations are consistent with the units and the stoichiometry of the reaction.

Key Concepts

Photosynthesis

Photosynthesis is the biochemical process by which green plants, algae, and some bacteria convert light energy into chemical energy, specifically glucose, using carbon dioxide and water. This process occurs primarily in the chloroplasts of plant cells and involves two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle). Understanding this process is crucial for analyzing the overall reaction and its energy changes.

Bond Dissociation Energy

Bond dissociation energy (BDE) is the energy required to break a specific bond in a molecule, resulting in the formation of separate atoms or radicals. It is a key concept in thermochemistry, as it helps estimate the enthalpy change (∆H) of a reaction by comparing the total energy of bonds broken in reactants to the total energy of bonds formed in products. Accurate BDE values are essential for calculating the energy changes in the photosynthesis reaction.

Enthalpy Change (∆H)

Enthalpy change (∆H) is a measure of the total heat content of a system and indicates the energy absorbed or released during a chemical reaction at constant pressure. In the context of photosynthesis, calculating ∆H involves determining the difference between the bond energies of reactants and products. This value is crucial for understanding the energy dynamics of the reaction and its feasibility, as well as for converting between different energy units like kcal/mol and kJ/mol.