11.22 Answer the following questions based on the P – T phase diagram of CO₂:

(a) CO₂ at 1 atm pressure and temperature – 60 °C is compressed isothermally. Does it go through a liquid phase ?

(b) What happens when CO₂ at 4 atm pressure is cooled from room temperature at constant pressure ?

(c) Describe qualitatively the changes in a given mass of solid CO₂ at 10 atm pressure and temperature –65 °C as it is heated up to room temperature at constant pressure.

(d) CO₂ is heated to a temperature 70 °C and compressed isothermally. What changes in its properties do you expect to observe?

<p><strong>11.22</strong></p><p><picture><img src="https://images.shiksha.com/mediadata/images/articles/1729159102phpxxlKuY.jpeg" alt="" width="266" height="181"></picture></p><p>The fusion and boiling points are given by the intersection point where this parallel line cuts the fusion and vaporization curves. It departs from ideal gas behavior as pressure increases.</p><p><strong> (a)</strong> At 1 atm pressure and at – 60 °C, it lies left of -56.6 <span title="Click to copy mathml"><math><mi>? </mi></math></span> (triple point O). Hence, it lies in the region of vapour and solid phases. Thus, &nbsp;CO₂&nbsp;condenses into solid state directly, without going through liquid phases.</p><p><strong> (b)</strong> At 4 atm pressure, &nbsp;CO₂ lies below 5.11 atm (triple point O). Hence it lies in the region of vaporous and solid phases. Thus, CO₂condenses into solid state directly, without going through liquid state.</p><p><strong> (c)</strong> When the temperature of a mass of solid &nbsp;CO₂ ( at 10 atm pressure and at -65 <span title="Click to copy mathml"><math><mi>? </mi></math></span> is increased, it changes to the liquid phase and then to the vaporous phase. It forms a line parallel to the temperature axis at 10 atm. The fusion and boiling points are given by the intersection point where this parallel line cuts the fusion and vaporization curves.</p><p><strong> (d)</strong> If CO2 is heated to 70 <span title="Click to copy mathml"><math><mi>? </mi><mo>)</mo><mi></mi></math></span>&nbsp;compressed isothermally, then it will not exhibit any transition to the liquid state. This because 70&nbsp;<span title="Click to copy mathml"><math><mi>? </mi><mi></mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">n</mi><mi mathvariant="normal">d</mi><mi mathvariant="normal"></mi></math></span> is higher than the critical temperature of &nbsp;CO₂. It will remain in the vapour state, but will depart from its ideal behavior as pressure increases.</p>

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