Phosphorus pentachloride forms from phosphorus trichloride and chlorine:
(a) Use data in Appendix B to calculate ∆S_sys, ∆S_surr, and ∆S_total for this reaction. Is the reaction spontaneous under standard-state conditions at 25 °C?

Entropy is a measure of the disorder or randomness in a system. In thermodynamics, the change in entropy (∆S) can indicate the spontaneity of a reaction; a positive ∆S suggests an increase in disorder, which often favors spontaneity. Calculating ∆S for a reaction involves considering the entropy of the products and reactants, and it is crucial for determining the overall behavior of the system.

Gibbs Free Energy (∆G) is a thermodynamic potential that helps predict whether a reaction will occur spontaneously at constant temperature and pressure. The relationship between Gibbs Free Energy and entropy is given by the equation ∆G = ∆H - T∆S, where ∆H is the change in enthalpy and T is the temperature in Kelvin. A negative ∆G indicates that a reaction is spontaneous, making it essential for evaluating the spontaneity of the given reaction.

Standard-state conditions refer to a set of specific conditions used to measure and compare thermodynamic properties, typically defined as 1 bar of pressure and a specified temperature, usually 25 °C. Under these conditions, the standard entropies and enthalpies of substances can be found in tables, allowing for consistent calculations of thermodynamic changes in reactions. Understanding these conditions is vital for accurately assessing the spontaneity of the reaction in question.