Use the information in Table 9.2 to calculate ΔH° in kilojoules for the photosynthesis of glucose (C6H12O6) and O2 from CO2 and liquid H2O, a reaciton carried out by all green plants

Verified step by step guidance

1. Identify the balanced chemical equation for the photosynthesis of glucose: \[ 6 \text{CO}_2 (g) + 6 \text{H}_2\text{O} (l) \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 (s) + 6 \text{O}_2 (g) \]
2. Use the standard enthalpy of formation (\( \Delta H_f^\circ \)) values from Table 9.2 for each compound involved in the reaction.
3. Calculate the total \( \Delta H_f^\circ \) for the products: \( \Delta H_f^\circ (\text{C}_6\text{H}_{12}\text{O}_6) + 6 \times \Delta H_f^\circ (\text{O}_2) \). Remember that the \( \Delta H_f^\circ \) for elements in their standard state, like \( \text{O}_2 \), is zero.
4. Calculate the total \( \Delta H_f^\circ \) for the reactants: \( 6 \times \Delta H_f^\circ (\text{CO}_2) + 6 \times \Delta H_f^\circ (\text{H}_2\text{O}) \).
5. Determine \( \Delta H^\circ \) for the reaction using the formula: \( \Delta H^\circ = \sum \Delta H_f^\circ (\text{products}) - \sum \Delta H_f^\circ (\text{reactants}) \).

Key Concepts

Enthalpy Change (ΔH°)

Enthalpy change (ΔH°) is the heat content change of a system at constant pressure during a chemical reaction. It indicates whether a reaction is exothermic (releases heat, ΔH° < 0) or endothermic (absorbs heat, ΔH° > 0). In the context of photosynthesis, calculating ΔH° helps determine the energy required or released when converting reactants like CO2 and H2O into glucose and O2.

Standard State Conditions

Standard state conditions refer to a set of specific conditions (usually 1 atm pressure and a specified temperature, typically 25°C) under which thermodynamic measurements are made. These conditions allow for consistent comparison of thermodynamic data, such as enthalpy values. When calculating ΔH° for reactions like photosynthesis, it is essential to ensure that all substances are in their standard states.

Hess's Law

Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for individual steps, regardless of the pathway taken. This principle allows chemists to calculate ΔH° for complex reactions by using known enthalpy changes of simpler reactions. In the case of photosynthesis, Hess's Law can be applied to derive the overall enthalpy change from the enthalpy values of the formation of reactants and products.