Simply put, this equation is used to determine Heat of Vaporization of a liquid given 2 vapor pressures and 2 temperatures.
Here is the equation
which useful for the C.C. Lab
for C.C. problems we use
There are a few things you must watch out for.
DH is in joules/mol, you will most likely get it in kJ/mol so convert it.
R= 8.314 J/mol K (notice the J)
T must be in Kelvin
The 2 vapor pressures must have the same unit.
Most problems give you a "NORMAL" boiling point. You have to be clever enough to get the hint.
normal boiling points occur at normal pressures....760 torr (the question hide the pressure...very sneaky)
This is the piece most students miss. Also make sure you change kJ/mol to J/mol.
1.The heat of vaporization of water is 44.01kJ.mol and the normal boiling point of water is 100.oC. Calculate the atmospheric pressure in Denver where the boiling point is 97.10oC.
Covert 44.01kJ/mol to 44,010J/mol
T1= 100 +273=373K and since it is normal boiling point P1 is 760 torr
T2=97.10 + 273=370.10 and we are solving for P2
plug and chug
2. The Vapor Pressure of Bromine (Br2) is 100.0 torr at 9.30oC and the enthalpy of vaporization is 30.91kJ/mol. Calculate the normal boiling point of Br2.
Convert 30.91kj/mol to 30,910J/mol
T1= 9.30+273= 282.30 and P1 is 100.0torr
T2 is the normal boiling point therefore P2 is normal pressure, so 760. torr.
Plug and chug
T1=331K or 58oC