Phosgene, COCl2, can be formed by the reaction of chloroform, CHCl3(l), with oxygen: 2 CHCl

step 1 can calculate the standard entropy change using the Gibb Hemholtz equation, where we rearrange f

Phosgene, COCl2, can be formed by the reaction of...

Phosgene, $\mathrm{COCl}_{2}$, can be formed by the reaction of chloroform, $\mathrm{CHCl}_{3}(l),$ with oxygen: $$ \begin{array}{l} 2 \mathrm{CHCl}_{3}(l)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{COCl}_{2}(g)+2 \mathrm{HCl}(g) \\ \Delta H^{\circ}=-353.2 \mathrm{~kJ} ; \Delta G^{\circ}=-452.4 \mathrm{~kJ} \text { at } 25^{\circ} \mathrm{C} \end{array} $$ (a) Calculate $\Delta S^{\circ}$ for the reaction. Is the sign reasonable? (b) Calculate $S^{\circ}$ for phosgene. (c) Calculate $\Delta H_{\mathrm{f}}^{\circ}$ for phosgene.

Phosgene, $\mathrm{COCl}_{2}$, can be formed by the reaction of chloroform, $\mathrm{CHCl}_{3}(l),$ with oxygen:
$$
\begin{array}{l}
2 \mathrm{CHCl}_{3}(l)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{COCl}_{2}(g)+2 \mathrm{HCl}(g) \\
\Delta H^{\circ}=-353.2 \mathrm{~kJ} ; \Delta G^{\circ}=-452.4 \mathrm{~kJ} \text { at } 25^{\circ} \mathrm{C}
\end{array}
$$
(a) Calculate $\Delta S^{\circ}$ for the reaction. Is the sign reasonable?
(b) Calculate $S^{\circ}$ for phosgene.
(c) Calculate $\Delta H_{\mathrm{f}}^{\circ}$ for phosgene.

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Key Concepts

Gibbs Free Energy Equation

This key concept is the fundamental relation ?G = ?H - T?S, which connects the change in free energy of a reaction to its enthalpy and entropy changes at a given temperature. It is crucial for analyzing reaction spontaneity and for calculating unknown thermodynamic parameters when two of the three quantities are known.

Standard Molar Entropy

Standard molar entropy (S°) is the measure of the randomness or disorder of a substance at a standard state (usually 1 bar, and a specified temperature such as 25°C). It is used in conjunction with the Gibbs free energy equation to determine entropy changes during a chemical reaction and to derive the absolute entropy of individual species.

Standard Enthalpy of Formation and Hess's Law

The standard enthalpy of formation (?Hf°) is defined as the heat change that results when one mole of a compound is formed from its elements in their standard states. Hess's Law is often applied to calculate ?Hf° for a reaction by combining known enthalpy changes of related reactions, emphasizing that enthalpy is a state function. This concept is key to determining the energy requirements or releases in chemical processes.

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