Question

the vapour of a pure substance when cooled unde air pressure less than its triple point pressure. a) it liquefies b) liquefies first and then solidifies c) remains unchanged d) solidifies directly ? which one

Answer 1

The critical temperature of a substance is the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied.

Every substance has a critical temperature. Some examples are shown below.

substancecritical temperature (oC)NH3132O2-119CO231.2H2O374 

Answer 2

Given that,

The vapour of a pure substance when cooled unde air pressure less than its triple point pressure.

We know that,

Critical pressure :

When a gas liquefy at critical temperature through the pressure it is called critical pressure.

For example :

The name of substance with critical pressure is,

$NH_{3}=111.5\ atm$

$O_{2}=49.7\ atm$

$CO_{2}=73.0\ atm$

Hence, The vapour of a pure substance is liquefies.