In Albuquerque, New Mexico, the typical atmospheric pressure is 625 torr. What i
ID: 961595 • Letter: I
Question
In Albuquerque, New Mexico, the typical atmospheric pressure is 625 torr. What is the boiling point of water (Hvap = 40.7 kJ/mol) in Albuquerque? (Assume the normal boiling point of water is 100.°C.)
K
What pressure would have to be applied to steam at 345°C to condense the steam to liquid water?
atm
Explanation / Answer
Part A
Using,
ln(P2/P1) = dHvap/R [1/T1 - 1/T2]
with,
P1 = 760 torr
P2 = 625 torr
T1 = 100 + 273 = 373 K
T2 = ?
dHvap = 40.7 kJ/mol
R = gas constant
we get,
ln(625/760) = 40700/8.314 [1/373 - 1/T2]
T2 = 378.64 K = 105.64 oC is the boiling point at this pressure
Part B
Using,
ln(P2/P1) = dHvap/R [1/T1 - 1/T2]
with,
P1 = 760 torr
P2 = ?
T1 = 100 + 273 = 373 K
T2 = 345 + 273 = 618 K
dHvap = 40.7 kJ/mol
R = gas constant
we get,
ln(P2/760) = 40700/8.314 [1/373 - 1/618]
P2 = 138180 torr is the pressure at which steam condenses to liquid water