Question

When CO\(_2\) and liquid water are brought in contact with each other, they may form solid hydrates. The three-phase hydrate boundary is shown in the Pressure-Temperature plot given below. Identify the correct statements. 

• A. Hydrates are stable in region I
• B. Hydrates are stable in region II
• C. Hydrates are stable in region III
• D. Hydrates are stable in region IV

Hint:

Hydrates form under specific pressure and temperature conditions where CO\(_2\) and water can coexist in a stable solid phase. Look for regions in the plot where the hydrate phase (H) is present.

Answer 1

The Correct Option is B, D

The Pressure-Temperature diagram shown in the question represents the phase boundary between different phases of CO\(_2\) (gas, liquid, and hydrate) and water (liquid).
1. Region I: This region represents a state where the CO\(_2\) is in the gas phase and the water is in the liquid phase. Hydrates are not stable in this region because the temperature and pressure conditions are not favorable for hydrate formation.
2. Region II: This is the region where the hydrate phase (H) of CO\(_2\) and H\(_2\)O can exist. At the pressures and temperatures in this region, CO\(_2\) gas and water are in contact and solid hydrates are stable. Therefore, hydrates are stable in region II.
3. Region III: This region corresponds to the coexistence of CO\(_2\) in its liquid phase and water in the liquid phase. While hydrates may exist under these conditions, the temperature and pressure here are generally not conducive to the stability of hydrates. Therefore, hydrates are not stable in region III.
4. Region IV: This region represents the boundary where CO\(_2\) exists as a liquid and water as a hydrate, with solid hydrate formation occurring at higher pressures. This region is also favorable for the formation of hydrates. Therefore, hydrates are stable in region IV.
Thus, the correct answers are (B) Hydrates are stable in region II and (D) Hydrates are stable in region IV.