Finding Vapor Pressure of Acetic Acid

mickey4

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9 years ago

What is the vapor pressure (in mmHg ) of acetic acid at 40 ∘ C ?
Acetic acid has a normal boiling point of 118 ∘ C and a ΔH vap of 23.4 kJ/mol .
I'm not sure how to go about starting.

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rsb

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9 years ago

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Acetic acid has a normal boiling point of 118 ∘C and a ΔHvap of 23.4 kJ/mol. What is the vapor pressure (in mmHg) of acetic acid at 35∘C?

Answer

You need the Clausius Clapeyron equation. P1 and T1 are x and 35C (308K), and P2 and T2 are 760 torr and 118C (391K). When we say the "normal boiling point" it is understood that the pressure is standard pressure, or 760 torr.

ln(P1/P2) = (ΔHvap / R)(1/T2 - 1/T1)
ln (x torr / 760 torr) = (23.4x10^3 J/mol / 8.314 J/molK) (1 / 391K - 1 / 308K)
(some algebra goes here)
x = 109

The vapor pressure at 35C is 109 torr.

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bio_man

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rsb

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9 years ago

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Acetic acid has a normal boiling point of 118 ?Cand a ?Hvap of 23.4 kJ/mol.

What is the vapor pressure (in mmHg) of acetic acid at 10?C?

Express your answer using three significant figures.

Answer

Clausius-Claperyon equation: ln(P2/P1) = (-DHvap/R) x (1/T2 - 1/T1)

At normal boiling point:

T1 = 118 deg C = 391.15 K, P1 = atmospheric pressure = 760 mmHg

T2 = 10 deg C = 283.15 K, P2 = ?

R = 8.314 J/mol.K

DHvap = 23.4 kJ/mol = 23400 J/mol

Substituting into equation:

ln(P2/760) = (-23400/8.314) x (1/283.15 - 1/391.15) = -2.74454

P2/760 = exp(-2.74454) = 0.06428

Vapor pressure P2 = 48.9 mmHg

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bio_man

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mickey4 Author

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9 years ago

Thank you! That really helped!

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