In 1774 Joseph Priestley prepared the element oxygen by heating mercury(II) oxide: HgO(s) → Hg(l) + ½O2(g)
For this reaction, ΔH° = 90.84 kJ and ΔS° = 108 J/K. Which of the following statements is true?

Question

Quizplus · Accepted Answer

The spontaneity of a reaction can be determined by the Gibbs free energy change, which is given by the equation ΔG° = ΔH° - TΔS°, where T is the temperature in Kelvin. For a spontaneous reaction, ΔG° must be negative.
Using the given values, ΔG° = 90.84 kJ - (298 K)(0.108 kJ/K) = 56.65 kJ. Since ΔG° is positive, the reaction is non-spontaneous under standard conditions (1 atm, 25°C). As the temperature increases, TΔS° becomes more positive and will eventually overcome ΔH°, making ΔG° negative and the reaction spontaneous. Thus, the reaction is spontaneous only at high temperatures.

In 1774 Joseph Priestley Prepared the Element Oxygen by Heating