Phosgene, COCl2, was used as a war gas during World War I....

Phosgene, $\mathrm{COCl}_{2}$, was used as a war gas during World War I. It reacts with the moisture in the lungs to produce $\mathrm{HCl}$, which causes the lungs to fill with fluid, and CO, which asphyxiates the victim. Both lead ultimately to death. For $\mathrm{COCl}_{2}(g), \quad S^{\circ}=284 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}$ and $\Delta H_{\mathrm{f}}^{\circ}=-223 \mathrm{~kJ} / \mathrm{mol}$. Use this information and the data in Table 18.1 to calculate $\Delta G_{\mathrm{f}}^{\circ}$ for $\mathrm{COCl}_{2}(g)$ in $\mathrm{kJ} \mathrm{mol}^{-1}$.

Phosgene, $\mathrm{COCl}_{2}$, was used as a war gas during World War I. It reacts with the moisture in the lungs to produce $\mathrm{HCl}$, which causes the lungs to fill with fluid, and CO, which asphyxiates the victim. Both lead ultimately to death. For $\mathrm{COCl}_{2}(g), \quad S^{\circ}=284 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}$ and
$\Delta H_{\mathrm{f}}^{\circ}=-223 \mathrm{~kJ} / \mathrm{mol}$. Use this information and the data
in Table 18.1 to calculate $\Delta G_{\mathrm{f}}^{\circ}$ for $\mathrm{COCl}_{2}(g)$ in $\mathrm{kJ} \mathrm{mol}^{-1}$.

Key Concepts

Relationship between ?G, ?H, and ?S

The fundamental thermodynamic relationship ?G = ?H - T?S links Gibbs free energy, enthalpy, and entropy, where T is the absolute temperature. This equation is central in predicting whether a reaction will occur spontaneously by balancing the enthalpy change (energy) and the entropy change (disorder) in the system. Its use is widespread in chemical thermodynamics to analyze and calculate standard free energies of formation and reaction.

Entropy (S)

Entropy quantifies the degree of disorder or randomness in a system. In thermodynamics, it plays a crucial role in determining the spontaneity of processes, as an increase in entropy generally favors a reaction’s progress. Standard entropy values are used in conjunction with other thermodynamic parameters to assess overall feasibility of reactions.

Gibbs Free Energy (?G)

Gibbs free energy is a thermodynamic potential that measures the maximum amount of useful work obtainable from a process at constant temperature and pressure. It provides a criterion for spontaneity, where negative values indicate that a process or reaction can occur spontaneously. Calculating ?G from other thermodynamic quantities helps predict reaction spontaneity in various chemical processes.

Enthalpy (?H)

Enthalpy is a measure of the total heat content of a system and represents the energy absorbed or released during a chemical reaction at constant pressure. The standard enthalpy of formation refers to the energy change when one mole of a compound is formed from its elements in their standard states. This concept is essential for understanding energy changes in chemical reactions.

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