Mark for Review What\'s This? At 1 atm pressure, substance A boils at -13 degree

Question

Mark for Review What's This? At 1 atm pressure, substance A boils at -13 degree C and substance B boils at -40 degree C. Which has the higher enthalpy of vaporization? Substance B Impossible to tell from the information given Substance A Mark for Review What's This? The enthalpy of vaporization of substance X is 30.0 kj/mol and its normal boiling point is -139 degree C. What is the vapor pressure of substance X at -166 degree C? 0.99 atm 68 atm 880 atm 0.015 atm 0.0011 atm Mark for Review What's This? Consider the phase diagram for substance X (attached). Initially, the sample is held at -63 degree C and 24.2 atm Then, the temperature is held constant at -63degree C and the pressure is decreased by 10.1 atm. When of the following phrases best describes what happened?

Explanation / Answer

Q7

This is impossible to tell... because we need at least 2 points in the equilibrium to stablish a line.

according to clasius clapeyron

ln(P2/P1) = dH/R*(1/t1-1/T2)

therefore, we need at least 2 poitns to compare dH

Q8

Apply:

H = 30 kJ/ml = 30000 J/mol

T1 = -139°C = 134K

P1 = 1 atm

T2 = -166 = 107K

Apply equation

ln(P2/P1) = dH/R*(1/t1-1/T2)

ln(P2/1) = (30000/8.314)(1/(134) - 1/(107))

solve for P2

P2 = exp(-6.794952) = 0.00111941 atm

answer is E

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