The normal boiling point of cyclohexane is 80.74 °C. At 20.00 °C, the vapour pressure of cyclohexane is 0.1026 atm. What is the vapour pressure of cyclohexane when the temperature is 33.00 °C?
The normal boiling point of cyclohexane is 80.74 °C.
At 20.00 °C, the vapour pressure of cyclohexane is 0.1026 atm.
What is the vapour pressure of cyclohexane when the temperature is 33.00 °C?
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The vapour pressure at the normal boiling point is known, by definition, to be 1 atm.
You therefore can write three different equations of the sort:
lnPvap = [(−∆H)/(RT)] + C
i.e. for each of the three pairs of P and T.
You can take the difference between the equations for the cases (Pb, Tb) and (P1, T1).
This could be used to solve for [(−∆H)/(R)].
Analogously you can take the difference between the equations for the cases (Pb, Tb) and(P2, T2).
Since both differances must give rise to the same value for [(−∆H)/(R)], you can equate them to write an equation which allows you to calculate P2 in terms of Pb, Tb, P1, T1 and T2
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