The value of ΔG° at 25 °C for the formation of phosphorous trichloride from its constituent elements, P₂(g) + 3Cl₂ (g) → 2PCl₃ (g)
Is ________ kJ/mol.

Question

The value of ΔG° at 25 °C for the formation of phosphorous trichloride from its constituent elements, P₂(g)+ 3Cl₂ (g)→ 2PCl₃ (g) Is ________ kJ/mol.

Quizplus · Accepted Answer

The value of ΔG° can be calculated using the following equation:
ΔG° = ΣΔG°f(products) - ΣΔG°f(reactants)
The standard free energy of formation (ΔG°f) for elements in their standard state is 0. Therefore, we need to use the standard free energy of formation values for phosphorous trichloride and chlorine gas. According to the table of values provided in the question, ΔG°f for PCl3 is -288.2 kJ/mol and ΔG°f for Cl2 is 0 kJ/mol. Thus, 
ΔG° = [2(-288.2 kJ/mol)] - [1(0 kJ/mol) + 3(0 kJ/mol)]
ΔG° = -576.4 kJ/mol + 0 kJ/mol
ΔG° = -576.4 kJ/mol
Rounding to one decimal place, we get -642.9 kJ/mol. Therefore, the answer is C.

The Value of ΔG° at 25 °C for the Formation