Question

The normal boiling point of acetone is 56.2EC. The ÄH_vap of acetone is 32.0 kJ/mol

-What is the vapor pressure of acetone at its normal boiling point?

-Is the vapor pressure of acetone at 20.0EC higher or lower than at 56.2EC?

-What is the vapor pressure of acetone at 20.0EC ?

Answer 1

We use Clauses clay Peron equation

T = 56.2 Deg C = 56.2 + 273.15 = 329.35 K

Ln p = (- delta H / R ) (1 / T)

Here R is gas constant = 8.314 J per K per mol

= (- 32.0 E3 J per mol / 8.314 J / K mol) (1/ 323.35 K )

P = 8.40 E -6 atm

Vapor pressure goes reverse as we increase the temperature so at 20.0 deg C vapor pressure would be lower.

Calculation of vapor pressure at 20.0 deg C = 293.15 K

Ln (P2/P1)=(-Delta H/ R ) x ( 1 /T2-1T1)

T1 = 56.2 Deg C = 56.2 + 273.15 = 329.35 K , p1 = 8.40 E-6 amt

P2 = ? (unknown ) , T2 = 293.15 K

Lets plug these value in above equation.

Ln (p2/8.40E-6)= (-32000/8.314) x ( 1/293.15 – 1/ 329.35))

P2 = 1.98 E-6   atm    It is less than the one at higher T.