Question

A.) The vapor pressure of a substance is 2.00x10^2 mmHg at 44.50 Celcius. What is its vapor pressure at 57 Celcius?

B.) At what temperature will the vapor pressure of the substance be 5 times the pressure at 35.5 Celcius?

Hvap = 49.6 kJ/mol

I know the answer to letter A is 407, I am just unsure of how to get the answer. Letter B I do not have an answer. Thank you in advance.

Answer #1

A)

T1 = 44.5 oC

=(44.5 + 273)K

= 317.5 K

T2 = 57 oC

=(57 + 273)K

= 330 K

P1 = 2*10^2 mmHg

ΔH = 49.6 KJ/mol

= 49600 J/mol

use:

ln(P2/P1) = (ΔH/R)*(1/T1 - 1/T2)

ln(P2/2*10^2) = (49600.0/8.314)*(1/317.5 - 1/330.0)

ln(P2/2*10^2) = 5966*(1.193*10^-4)

P2 = 407 mmHg

Answer: 407 mmHg

2)

T1 = 35.5 oC

=(35.5 + 273)K

= 308.5 K

P2/P1 = 5

ΔH = 49.6 KJ/mol

= 49600 J/mol

use:

ln(P2/P1) = (ΔH/R)*(1/T1 - 1/T2)

ln(5) = (49600/8.314)*(1/308.5 - 1/T2)

1.6094 = 5965.8408*(1/308.5 - 1/T2)

T2 = 337 K

= (337-273) oC

= 64 oC

Answer: 64 oC

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