In the vicinity of the triple point, the vapor pressures of liquid and solid ammonia are respectively given by
ln p = 15.16 - 3063/T and ln p = 18.70 - 3754/T
where p is in atmospheres and T is in Kelvin. What is the temperature at the triple point? Also calculate the triple point pressure.
Calculations:
At the triple point, all the phases (solid, liquid and vapor) exist in equilibrium.
Therefore, vapor pressure of liquid ammonia = vapor pressure of solid ammonia
15.16 - 3063/T = 18.7 - 3754/T
3754/T - 3063/T = 18.7 - 15.16
3754 - 3063 = T(18.7 - 15.16)
691 = 3.54T
T = 691/3.54 = 195.2 K
Triple point temperature = 195.2 K
Triple point pressure can be obtained from any of the vapor pressure to temperature relation.
By the vapor pressure to temperature relation of liquid ammonia,
ln p = 15.16 - 3063/195.2
p = 0.588 atm
Similarly, by the vapor pressure to temperature relation of solid ammonia,
ln p = 18.7 - 3754/195.2
p = 0.588 atm
Triple point pressure = 0.588 atm
Last Modified on: 01-May-2024
Chemical Engineering Learning Resources - msubbu
e-mail: learn[AT]msubbu.academy
www.msubbu.in