Which of the following processes are spontaneous?
a. the melting of ice cubes at −10 °C and 1 atm pressure
b. separating a mixture of N₂ and O₂ into two separate samples, one that is pure N₂ and one that is pure O₂
c. alignment of iron filings in a magnetic field
d. the reaction of hydrogen gas with oxygen gas to form water vapor at room temperature
e. the dissolution of HCl(g) in water to form concentrated hydrochloric acid

Key Concepts

Spontaneity in Chemical Processes

A spontaneous process is one that occurs without the need for external energy input. It is driven by the increase in the system's entropy or the decrease in its Gibbs free energy. Understanding spontaneity helps predict whether a reaction or physical change will occur under given conditions.

Entropy and Temperature

Entropy is a measure of the disorder or randomness in a system. As temperature increases, the entropy of a system typically increases, which can influence the spontaneity of processes. For example, the melting of ice at higher temperatures is spontaneous due to increased molecular motion and disorder.

Gibbs Free Energy

Gibbs free energy (G) combines enthalpy and entropy to determine the spontaneity of a process at constant temperature and pressure. A negative change in Gibbs free energy (ΔG < 0) indicates a spontaneous process, while a positive change (ΔG > 0) suggests non-spontaneity. This concept is crucial for evaluating chemical reactions and physical changes.