Answer: -
100 mm Hg
Explanation: -
P 1 =400 mm Hg
T 1 = 63.5 C + 273 = 336.5 K
T 2 = 34.9 C + 273 = 307.9 K
ΔHvap = 39.3 KJ/mol = 39.3 x 10³ J mol⁻¹
R = 8.314 J ⁻¹K mol⁻¹
Now using the Clausius Clapeyron equation
ln (P1 / P2) = ΔHvap / R x (1 / T2 - 1 / T1)
Plugging in the values
ln (400 mm/ P₂) = (39.3 x 10³ J mol⁻¹ / 8.314 J ⁻¹K mol⁻¹) x ([tex] \frac{1}{307.9 K} [/tex] - [tex] \frac{1}{336.5 K} [/tex]
= 1.38
P₂ = 100 mm Hg
The vapor pressure at the new temperature is 352 mmHg.
We can obtain the vapor pressure at different temperatures using the formula; ln(P1/P2) = (ΔHvap/R)((1/T2) - (1/T1)).
P1 = initial pressure
P2 = final pressure
ΔHvap = enthalpy of vaporization
R = gas constant
T1 = initial temperature
T2= final temperature
Substituting values;
ln(400/P2) = (39.3 × 10^3 J/mol/ 8.314 J/K.mol) (1/308 - 1/337)
ln(400/P2) = 0.128
(400/P2) = e^0.128
P2 = 400/e^0.128
P2 = 352 mmHg
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