The enthalpy of vaporization of a certain liquid is found to be 14.4 kJ mol-1 at 180 K, its normal boiling point. The molar volumes of the liquid and the vapour at the boiling point are 115 cm3 mol-1 and 14.5 dm3 mol-1, respectively. (a) Estimate dp/dT from the Clapeyron equation and (b) the percentage error in its value if the Clausius–Clapeyron equation is used instead.

Respuesta :

Answer :

(a) The value of [tex]\frac{dP}{dT}[/tex] is [tex]5.56\times 10^3Pa/K[/tex]

(b) The percentage error will be 2.5 %

Explanation :

(a) First we have to calculate the [tex]V_{vap}[/tex].

[tex]V_{vap}=V_2-V_1[/tex]

[tex]V_1[/tex] = volume of liquid = [tex]115cm^3mol^{1-}=115\times 10^{-6}m^3mol^{1-}[/tex]

[tex]V_1[/tex] = volume of vapor = [tex]14.5dm^3mol^{1-}=14.5\times 10^{-3}m^3mol^{1-}[/tex]

[tex]V_{vap}=V_2-V_1[/tex]

[tex]V_{vap}=(14.5\times 10^{-3}m^3mol^{1-})-(115\times 10^{-6}m^3mol^{1-})[/tex]

[tex]V_{vap}=1.44\times 10^{-2}m^3mol^{1-}[/tex]

Now we have to calculate the value of [tex]\frac{dP}{dT}[/tex]

The Clausius- Clapeyron equation is :

[tex]\frac{dP}{dT}=\frac{\Delta H_{vap}}{T\Delta V_{vap}}[/tex]

where,

T = temperature = 180 K

[tex]\Delta H_{vap}[/tex] = heat of vaporization = 14.4 kJ/mole = 14400 J/mole

[tex]V_{vap}=1.44\times 10^{-2}m^3mol^{1-}[/tex]

Now put all the given values in the above formula, we get:

[tex]\frac{dP}{dT}=\frac{(14400J/mole)}{(180K)\times (1.44\times 10^{-2}m^3mol^{1-})}\times \frac{1Pa}{1J/m^3}[/tex]

[tex]\frac{dP}{dT}=5.56\times 10^3Pa/K[/tex]

(b) Now we have to calculate the percentage error.

Now we have to calculate the value of [tex]\frac{dP}{dT}[/tex] at normal boiling point.

The Clausius- Clapeyron equation is :

[tex]\frac{dP}{dT}=\frac{\Delta H_{vap}}{T\Delta V_{vap}}[/tex]

As we know that : PV = nRT

So,

[tex]\frac{dP}{dT}=\frac{P\Delta H_{vap}}{RT^2}[/tex]

where,

R = gas constant = 8.314 J/K.mol

T = temperature = 180 K

[tex]\Delta H_{vap}[/tex] = heat of vaporization = 14.4 kJ/mole = 14400 J/mole

P = pressure at normal boiling point = 101325 Pa

Now put all the given values in the above formula, we get:

[tex]\frac{dP}{dT}=\frac{(101325Pa}\times (14400J/mole)}{(8.314J/K.mol)\times (180K)^2}[/tex]

[tex]\frac{dP}{dT}=5.42\times 10^3Pa/K[/tex]

Now we have to determine percentage error.

[tex]\%\text{ error}=\frac{(5.56\times 10^3Pa/K)-(5.42\times 10^3Pa/K)}{5.56\times 10^3Pa/K}\times 100[/tex]

[tex]\%\text{ error}=2.5\%[/tex]

Therefore, the percentage error will be 2.5 %