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Difficulty: MediumSulfur Allotropes, Hydrogen Sulfide, and Sulfur(IV) Oxide

Rhombic sulfur (α\alpha-sulfur) and monoclinic sulfur (β\beta-sulfur) are two well-known crystalline allotropes of sulfur. Which of the following statements correctly describes the stability and thermal transformation relationship between these two allotropes at standard atmospheric pressure?

  1. Above 96∘C96^\circ\text{C}, monoclinic sulfur is the stable crystalline form, whereas below 96∘C96^\circ\text{C}, rhombic sulfur is the stable crystalline form.Answer
  2. B
    Above 96∘C96^\circ\text{C}, rhombic sulfur is the stable crystalline form, whereas below 96∘C96^\circ\text{C}, monoclinic sulfur is the stable crystalline form.
  3. C
    Rhombic sulfur and monoclinic sulfur are chemical isomers that possess identical crystal lattices but different chemical formulas.
  4. D
    Monoclinic sulfur is an amorphous allotrope obtained by pouring boiling sulfur into cold water.

Answer

Above 96∘C96^\circ\text{C}, monoclinic sulfur is the stable crystalline form, whereas below 96∘C96^\circ\text{C}, rhombic sulfur is the stable crystalline form.
The transition temperature for the two main crystalline allotropes of sulfur is 96∘C96^\circ\text{C}. Below this temperature, rhombic sulfur (α\alpha-sulfur) is the thermodynamically stable form. When heated above 96∘C96^\circ\text{C}, rhombic sulfur slowly transforms into monoclinic sulfur (β\beta-sulfur), which remains stable up to its melting point of 119∘C119^\circ\text{C}.

Step-by-Step Solution

1
Identify the nature of the allotropes of sulfur.
Both rhombic sulfur (α\alpha-sulfur) and monoclinic sulfur (β\beta-sulfur) are crystalline allotropes made up of crown-shaped S8S_8 molecules.
Allotropes are different structural forms of the same element in the same physical state.
2
Determine the transition temperature between rhombic and monoclinic sulfur.
The transition temperature is 96∘C96^\circ\text{C}. At this temperature, both allotropes coexist in equilibrium.
Temperature determines which crystal lattice structure is thermodynamically stable.
3
Evaluate stability ranges above and below the transition temperature.
Rhombic sulfur is stable below 96∘C96^\circ\text{C}, while monoclinic sulfur is stable between 96∘C96^\circ\text{C} and its melting point (119∘C119^\circ\text{C}).
Heating rhombic sulfur above 96∘C96^\circ\text{C} slowly converts it to monoclinic sulfur needles.

Key Concept

Transition temperature and allotropy of crystalline sulfur
Estimated Time:1m 0s
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Topics

Sulfur Allotropes, Hydrogen Sulfide, and Sulfur(IV) Oxide

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