Question

Calculate the enthalpy of allotropic transformation from monoclinic to rhombic sulphur from the following data:

S(rhombic)+O₂(g)→SO₂(g)ΔrH∘=−294.1kJ
S(monoclinic)+O₂(g)→SO₂(g)ΔrH∘=−295.4kJ

Answer 1

The enthalpy of allotropic transformation from monoclinic to rhombic sulfur is calculated to be -1.3 kJ/mol, indicating an exothermic reaction where energy is released during the transformation.

Step-by-step explanation:

The student's question is about calculating the enthalpy of allotropic transformation from monoclinic to rhombic sulfur using given reaction enthalpies.

First, we can consider the enthalpy changes (ΔH°) for the formation of sulfur dioxide (SO2) from rhombic sulfur and from monoclinic sulfur:

• Rhombic S + O2(g) → SO2(g), ΔH° = -294.1 kJ
• Monoclinic S + O2(g) → SO2(g), ΔH° = -295.4 kJ

We need to find the difference in enthalpy (ΔH) between the formation of SO2 from each allotrope of sulfur:

ΔH = ΔH°(monoclinic) - ΔH°(rhombic)

ΔH = (-295.4 kJ) - (-294.1 kJ)

ΔH = -1.3 kJ

This negative value indicates that the transformation from rhombic to monoclinic sulfur releases 1.3 kJ of energy per mole of sulfur under standard conditions. This result matches with the fact that the conversion of rhombic sulfur (Sα) to monoclinic sulfur (Sβ) is actually endothermic, requiring 0.401 kJ/mol to make the transformation, as mentioned in the reference information. Hence, reversing this process, which is what we calculated, would be exothermic, releasing energy.