Given below are two statements.
Statement I: alpha and beta-forms of sulphur can change reversibly b

Q: What exactly is the transition temperature of sulphur?

The transition temperature is $369 \text{ K}$. Below this temperature, Rhombic sulphur ($S_\alpha$) is stable. Above this temperature, Monoclinic sulphur ($S_\beta$) is stable.

Q: Why is rhombic sulphur's standard enthalpy of formation zero?

In thermodynamics, the most stable state of an element at standard conditions ($298 \text{ K}$ and $1 \text{ atm}$) is assigned an enthalpy of formation of zero. Since rhombic sulphur is the most stable allotrope at room temperature, its $\Delta_f H^\circ = 0$.

Q: Can monoclinic sulphur exist at room temperature at all?

Yes, but only temporarily. If you cool monoclinic sulphur quickly to room temperature, it becomes 'metastable'. Over time, it will slowly and spontaneously convert back into the more stable rhombic form.

Q: Do both of these allotropes have the same molecular formula?

Yes! Both rhombic and monoclinic sulphur consist of $S_8$ molecules, which are shaped like puckered rings (often called a crown shape). The difference lies only in how these $S_8$ rings are packed together in the crystal lattice.

Q: Are there any other allotropes of sulphur besides these two?

Absolutely. Sulphur has many allotropes. For example, if you pour boiling sulphur into cold water, you get 'plastic sulphur' (an amorphous form). There are also cyclo-$S_6$ rings (Engel's sulphur), but rhombic and monoclinic are the most important crystalline forms for JEE.

Question

Given below are two statements.
Statement I $\alpha$ and $\beta$-forms of sulphur can change reversibly between themselves with slow heating or slow cooling.
Statement II At room temperature, the stable crystalline form of sulphur is monoclinic sulphur.
In the light of the above statements, choose the correct answer from the options given below.

Options:

(A) Both statements I and II are true.

(B) Both statements I and II are false.

(C) Statement I is true but statement II is false.

(D) Statement I is false but statement II is true.

Sigma Percentile · Accepted Answer

### The Tale of Two Sulphurs

Sulphur is a fascinating element that loves to play dress-up. In its solid state, it primarily exists in two distinct crystalline forms, or allotropes: **Rhombic Sulphur** (also known as $S_\alpha$) and **Monoclinic Sulphur** (known as $S_\beta$).

Imagine these two forms as two different architectural arrangements of the exact same building blocks (the $S_8$ puckered rings). The beauty of these allotropes is that they are not permanently locked into their structures. They can actually transform into one another depending on the temperature.

### The Magic Number: 369 K

The gateway between these two forms is a very specific temperature: **$369 	ext{ K}$** (which is about $96^\circ	ext{C}$). This is known as the transition temperature.

If you take a beautiful, yellow crystal of rhombic sulphur and slowly heat it above $369 	ext{ K}$, the molecules rearrange themselves, and it transforms into the needle-like crystals of monoclinic sulphur.

Conversely, if you take that monoclinic sulphur and let it cool down below $369 	ext{ K}$, it will slowly revert back to the rhombic form. This means the transformation is completely reversible.

$$S_\alpha ightleftharpoons S_\beta$$

Because of this beautiful reversible dance upon heating and cooling, **Statement I is absolutely true**.

### The Reality of Room Temperature

Now, let's bring this down to our everyday reality. Room temperature is generally considered to be around $298 	ext{ K}$ ($25^\circ	ext{C}$).

Ask yourself: is $298 	ext{ K}$ above or below the transition temperature of $369 	ext{ K}$? It is significantly below it.

Since rhombic sulphur ($S_\alpha$) is the form that exists stably below $369 	ext{ K}$, it must be the stable form at room temperature. In fact, rhombic sulphur is the thermodynamically most stable allotrope of sulphur at standard conditions. Because of its supreme stability, its standard enthalpy of formation is taken as zero ($\Delta_f H^\circ = 0$).

Statement II claims that monoclinic sulphur is the stable form at room temperature. Based on our logic, this is completely backwards. Monoclinic sulphur cannot survive indefinitely at room temperature; it will eventually transform back into rhombic sulphur. Therefore, **Statement II is false**.

### Final Conclusion

By understanding the thermal relationship between $S_\alpha$ and $S_\beta$, we can confidently conclude that Statement I is true, while Statement II is false. This makes option (c) the correct choice.

Select Answer:

Visualized Solution

$S_{α} and S_{β} Allotropes$

$Reversible Transition$

$Heating and Cooling$

$Room Temperature Stability$

$Conclusion$

$Thermodynamic Stability$

The Sigma Insight: Group 16 Elements

The Tale of Two Sulphurs

The Magic Number: 369 K

The Reality of Room Temperature

Final Conclusion

Similar Questions

Among the following allotropic forms of sulphur, the number of allotropic forms, which will show paramagnetism is ......... (a) $α$ -sulphur (b) $β$ -sulphur (c) $S_{2}$ -form

Which of the following statements regarding sulphur is incorrect?

The number of bonds between sulphur and oxygen atoms in $S_{2} O_{8}^{2 -}$ and the number of bonds between sulphur and sulphur atoms in rhombic sulphur, respectively, are

In polythionic acid, $H_{2} S_{x} O_{6}$ ( $x = 3$ to $5$ ) the oxidation state(s) of sulphur is/are

Which of the following is wrong statement?

The oxoacid of sulphur that does not contain bond between sulphur atoms is

The product obtained from the electrolytic oxidation of acidified sulphate solutions, is

Consider the sulphides $HgS$ , $PbS$ , $CuS$ , $Sb_{2} S_{3}$ , $As_{2} S_{3}$ and $CdS$ . Number of these sulphides soluble in $50% HNO_{3}$ is

Chalcogen group elements are

The correct order of electron gain enthalpy is