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Question
Why does the boundary between liquid phase and gaseous phase disappear on heating a liquid upto critical temperature in a closed vessel? In this situation what will be the state of the substance?
Solution
The boundary between the liquid phase and gaseous phase disappear on heating a liquid up to critical temperature in a closed vessel because at the critical point the densities of liquid and the vapour become equal. The fluid at this stage is called ‘supercritical fluid’
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RELATED QUESTIONS
The critical temperature for carbon dioxide and methane are 31.1 °C and –81.9 °C respectively. Which of these has stronger intermolecular forces and why?
Gases possess characteristic critical temperature which depends upon the magnitude of intermolecular forces between the particles. Following are the critical temperatures of some gases.
| Gases | \[\ce{H2}\] | \[\ce{He}\] | \[\ce{O2}\] | \[\ce{N2}\] |
| Critical temperature in Kelvin | 33.2 | 5.3 | 154.3 | 126 |
From the above data what would be the order of liquefaction of these gases? Start writing the order from the gas liquefying first
Two different gases ‘A’ and ‘B’ are filled in separate containers of equal capacity under the same conditions of temperature and pressure. On increasing the pressure slightly the gas ‘A’ liquefies but gas B does not liquify even on applying high pressure until it is cooled. Explain this phenomenon.
The critical temperature (Tc) and critical pressure (pc) of \[\ce{CO2}\] are 30.98°C and 73 atm respectively. Can \[\ce{CO2 (g)}\] be liquefied at 32°C and 80 atm pressure?
Assertion (A): Gases do not liquefy above their critical temperature, even on applying high pressure.
Reason (R): Above critical temperature, the molecular speed is high and intermolecular attractions cannot hold the molecules together because they escape because of high speed.
Assertion (A): At critical temperature liquid passes into gaseous state imperceptibly and continuously.
Reason (R): The density of liquid and gaseous phase is equal to critical temperature.
A gas can be liquefied:
Given below are the critical temperatures of some of the gases:
| Gas | Critical temperature (K) |
| He | 5.2 |
| CH4 | 190 |
| CO2 | 304.2 |
| NH3 | 405.5 |
The gas showing the least adsorption on a definite amount of charcoal is:
