[sadaf]

I want to know what is critical temperature, and pressure, it's the term often used, for steam and liquid too. Can any one explain it to me briefly?
what the difference b/w Normal temperature and pressure, standard temperature pressure,
in one case the temperature is taken as 60 F, in the other case it's taken as 25 C.
What is meant by superheated steam? how one can define superheated steam at 120 oC.

Thankyou in advance
waiting for your prestigiious response

[AWK]

http://en.wikipedia.org/wiki/Critical_point_(thermodynamics)

[eugenedakin]

Hi sadaf,

In addition to AWK's link here is another one.

http://en.wikipedia.org/wiki/Critical_temperature

Essentially, here is a way of explaining critical temperature:

Tc (Critical Temperature), of a material is the temperature above which distinct liquid and gas phases do not exist. As the critical temperature is approached, the properties of the gas and liquid phases become the same. Above the critical temperature, there is only one phase: that of supercritical fluid. The critical pressure is the vapor pressure at the critical temperature. The critical molar volume is the volume of one mole of material at the critical temperature and pressure. On diagrams showing thermodynamic properties for a given substance, the point at critical temperature and critical pressure is called the critical point of the substance. Above its critical temperature, a gas cannot be liquefied.

I hope this helps,

Eugene

[jebosa1]

Water exhibits particularly unusual behaviour beyond its critical temperature and pressure (374° C, 218 atmospheres). Above its critical temperature, the distinction between the liquid and gaseous states of water disappears—it becomes a supercritical fluid, the density of which can be varied from liquidlike to gaslike by varying its temperature and pressure.