Question

A Huap of hexane = 28.9 kJ/mol and the normal BP = 68.70 What is the vapor pressure of hexane @ 18°C a) 4470 mm Hg b) 400 mm Hg c) 188 mm Hg d) 129 mmity

Answer 1

Given that the normal boiling point is 68.7 ^oC

and the normal boiling point is temperature at which vapor pressure of liquid is equal to standard sea level atmospheric pressure i.e.. 760 mm of Hg. Let this vapor pressure is denotes by P₁

Let the vapor pressure at 18 ^oC be P₂

Now let's change the both temperature in kelvin.

T₁ =68.7^oC =68.7+273 = 341.7 k

T₂ = 18^oC =18+273 =291 k

Given that $\Delta$ H_vap= 28.9 kJ/mol = 28900 kJ/mol

The formula for vapor Pressure at two different temperature is following:

$1596123209349_blob.png$

Thus the vapor pressure will be 129 mm of Hg