Question

Which of the following processes are spontaneous: (a) the melting of ice cubes at \(10^{\circ} \mathrm{C}\) and 1 atm pressure; (b) separating a mixture of \(\mathrm{N}_{2}\) and \(\mathrm{O}_{2}\) into two separate samples, one that is pure \(\mathrm{N}_{2}\) and one that is pure \(\mathrm{O}_{2}\); (c) alignment of iron filings in a magnetic field; (d) the reaction of sodium metal with chlorine gas to form sodium chloride; (e) the dissolution of \(\mathrm{HCl}(g)\) in water to form concentrated hydrochloric acid?

Short answer

The spontaneous processes are: (a) the melting of ice cubes at \(10^{\circ} \mathrm{C}\) and 1 atm pressure, (c) alignment of iron filings in a magnetic field, (d) the reaction of sodium metal with chlorine gas to form sodium chloride, and (e) the dissolution of \(\mathrm{HCl}(g)\) in water to form concentrated hydrochloric acid.

Step-by-step solution

Process (a) - Melting of ice cubes at 10°C and 1 atm

: Ice cube melting means a phase transition going from solid ice to liquid water. The given condition is that the temperature is above its freezing/melting point, which is 0°C at 1 atm atmospheric pressure. Since the temperature is higher than its melting point, it means the ice would absorb heat and start to melt. Therefore, melting is a spontaneous process under these conditions.

Process (b) - Separating a mixture of N2 and O2

: In this process, we need to evaluate if separating a mixture of N2 and O2 into two pure samples of N2 and O2 occurs spontaneously. In general, gases tend to mix and naturally spread out, as they have natural tendency towards higher entropy. To separate the gases, it is required to apply a specific method or external influence. Hence, this process of separating N2 and O2 does not occur spontaneously.

Process (c) - Alignment of iron filings in a magnetic field

: Iron filings are made up of small particles of iron which are attracted to a magnetic field. When a magnetic field is introduced, the iron filings will align themselves along the magnetic field lines. In this case, the external influence is the magnetic field itself, and the alignment of iron filings will occur spontaneously under its influence.

Process (d) - Reaction of sodium metal with chlorine gas

: The reaction between sodium (Na) and chlorine (Cl2) is given as follows: \[ 2 \mathrm{Na}(s) + \mathrm{Cl}_{2}(g) \longrightarrow 2 \mathrm{NaCl}(s) \] This reaction is known to be highly exothermic, which means it releases a large amount of energy. Exothermic reactions typically occur spontaneously because they result in a decrease in the system's internal energy. Therefore, the reaction of sodium metal with chlorine gas to form sodium chloride is spontaneous.

Process (e) - Dissolution of HCl(g) in water

: The dissolution of HCl gas in water to form concentrated hydrochloric acid is an exothermic reaction that releases heat. It results in the formation of solvated hydrogen ions and chloride ions in solution: \[ \mathrm{HCl}(g) + \mathrm{H}_{2}\mathrm{O}(l) \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+}(aq) + \mathrm{Cl}^{-}(aq) \] As the process is exothermic and results in an increase in the system's entropy (the gas dissolves into an aqueous solution), the dissolution of HCl(g) in water is a spontaneous process.