Critical temperature and pressure
Thread Content
I read in some materials about the temperature and pressure required for ammonia to liquefy; one set of values for liquefaction pressure and temperature is approximately 13 kilograms per square centimeter, with a corresponding temperature of 35 degrees. Can it be understood in this way that ammonia can be liquefied at a temperature of 35 degrees when its pressure is above 13, or that it can be liquefied at a temperature below 35 degrees when its pressure is 13? Thank you
You must be referring to the saturated vapor pressure. When the temperature is constant, the vapor pressure will eventually stabilize at a fixed value; this vapor pressure is known as the saturated vapor pressure of ammonia at that temperature. When the value of the vapor pressure reaches that of the saturated steam pressure, ammonia molecules in the liquid phase continue to vaporize, and ammonia molecules in the vapor phase continue to condense into a liquid. Since the rate of vaporization of ammonia is equal to the rate of condensation of ammonia vapor, the amount of liquid does not decrease nor does the amount of gas increase; thus, a balance is achieved between the liquid and the gas.
At the saturated vapor pressure, ammonia gas and liquid ammonia are in dynamic equilibrium. As for obvious liquefaction/vaporization, ammonia can be liquefied as long as its temperature is higher/lower than the ambient temperature.