Question

1) The vapor pressure of liquid heptane, C₇H₁₆, is 40.0 mm Hg at 295 K.

A sample of C₇H₁₆ is placed in a closed, evacuated container of constant volume at a temperature of 450 K. It is found that all of the C₇H₁₆ is in the vapor phase and that the pressure is 74.0 mm Hg. If the temperature in the container is reduced to 295 K, which of the following statements are correct? chosse all that apply.

A) Some of the vapor initially present will condense.

B)  Liquid heptane will be present.

C) No condensation will occur.

D) The pressure in the container will be 48.5 mm Hg.

E) Only heptane vapor will be present.

Answer 1

Since vapor pressure of hapatane is 40.0 mm Hg at 295 K, above this pressure at 295 K any vapor present will be condensed.

So, if the pressure at 295 K is less than 40 mm Hg, no condensation is will occur.

If the pressure at 295 K is equal to 40 mm Hg, some of the vapor initially present will condense.

If the pressure at 295 K is greater than 40 mm Hg, all heptane will be condensed and Liquid heptane will be present.

Calculate the pressure at 295 K :

P₁/T₁ = P₂/T₂

P₁ and T₁ are inital pressure and temperature.

P₂ and T₂ are final pressure and temperature.

P₂ = (P₁/T₁)*(T₂ ) = (74.0 mmHg/450 K)*295 K = 48.5 mmHg

Correct options are: B and D