1. A similar experiment was performed in lab and was carried out by your instruc

Question

1. A similar experiment was performed in lab and was carried out by your instructor. THe data was collected and analyzed with the use of Excel. The equation of best fit line was y= -4058.7x + 16.10 . Using the equation of the best fit line, calculate the heat of vaporization ( Delta H vap) and the normal boiling point (in degrees C) of this volitile liquid. (The experiment pressure was measured in kPa not atm).

(Hint: What is the value of P vap when a liquid boils at its normal boiling point?)

I've calculated H vap, it is 33.7440318 kJ/mol

However, I need help in calculating the normal boiling point.

Also,

2. Using the answers from question 1, identify the volitile liquid based on the following data. Explain your reasoning.

Compound Normal Boiling Pt. ( Degrees C)            Delta H vap (kJ/mol)

Ethanol                    78.3                                                                    42.4

iso- Propanol         82.3                                                                   45.4

Cyclohexane           80.7                                                                   33.1

Please help me, or guide me to figuring out these questions... any help would be greatly appreciated. Thank you

Explanation / Answer

(1) The straight line (y = mx + c) is a plot of the Clausius-Claperyon equation:

ln(P) = (-DHvap/R) x (1/T) + c


where y = ln(P), x = 1/T, slope = m = (-DHvap/R) and y-intercept = c


Comparing with equation for best fit: y = -4058.7x + 16.10:

Slope = -DHvap/R = -4058.7


Heat of vaporization DHvap = -slope x R

= 4058.7 x 8.314

= 3.37 x 10^4 J/mol = 33.7 kJ/mol


At normal boiling point, vapor pressure P = atmospheric pressure = 1 atm = 101.325 kPa

Substituting value into equation:

ln(101.325) = -4058.7 x (1/T) + 16.10

1/T = 0.0028289

Boiling point T = 1/0.0028289 = 353.49 K = 80.3 deg C


(2) Experimental DHvap = 33.7 kJ/mol

Experimental boiling point = 80.3 deg C


Comparing experimental values with theoretical values, the closest match for the volatile liquid is

Cyclohexane:

Theoretical DHvap = 33.1 kJ/mol

Theoretical boiling point = 80.7 deg C

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