In 1774 Joseph Priestly prepared oxygen by heating mercury(II) oxide according to the reaction HgO(l) Hg(l) + ½O₂(g), for which ΔH^o = 90.84 kJ/mol and ΔS^o = 108 J/K.mol. Which of the following statements is true for this reaction?

Question

In 1774 Joseph Priestly prepared oxygen by heating mercury(II) oxide according to the reaction HgO(l) <----> Hg(l) + ½O₂(g), for which ΔH^o = 90.84 kJ/mol and ΔS^o = 108 J/K.mol. Which of the following statements is true for this reaction?

Quizplus · Accepted Answer

The spontaneity of a reaction is determined by the sign and magnitude of the Gibbs free energy change, ΔG. The equation relating ΔG to ΔH (enthalpy change) and ΔS (entropy change) is:

ΔG = ΔH - TΔS

where T is the temperature in Kelvin.

For a spontaneous reaction, ΔG must be negative. We can find ΔG for the given reaction at different temperatures using the equation above and the given values of ΔH and ΔS:

ΔG = 90.84 kJ/mol - T(108 J/K.mol)/1000 = 90.84 - 0.108T

At low temperatures (T<841 K), ΔG is negative and the reaction is spontaneous. At high temperatures (T>841 K), ΔG is positive and the reaction is non-spontaneous. Therefore, choice D is correct.

Choices A and B are incorrect because they imply that the spontaneity of the reaction depends only on temperature, which is not true. Choice C is incorrect because it implies that ΔG becomes more negative with increasing temperature, which is not true for this reaction. Choice E is incorrect because it implies that the reaction is at equilibrium at a specific temperature and pressure, which may not be true.

In 1774 Joseph Priestly Prepared Oxygen by Heating Mercury(II) Oxide