Standard Entropy of a liquid at melting point with no S(298.15) given

In summary, the vapour pressures of a liquid have been measured and fit to an equation, and the melting point has been determined to be 392.7 K. Using the Clausius Clapeyron equation, the enthalpy change (ΔH) for vaporization was calculated to be 68361 J/mol, with a corresponding entropy change (ΔS) of 229.29 J/mol K. Adding the given ΔSvap of 117.20 J/mol K does not give the expected answer of 350.60 J/mol K, and further calculations are needed to determine the correct value for ΔS.
  • #1
DiffusConfuse
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Homework Statement


Vapour pressures of a liquid have been measured and fit to the following equation:
Log10 P (mmHg) = -3571/T + 8.999
The melting point has been determined to be 392.7 K.
A Cp value given for the liquid is 250 J/mol K
and the ΔSvap is 117.20 J/mol K

Homework Equations


Clausius Clapeyron:

ln(P1/P2)= ΔH/R*(1/T2 - 1/T1)

The Attempt at a Solution



T1= 392.7 K P1 = 0.8045 mmHg (from the equation, giving the vapour pressure of the LIQUID at the melting point).
T2= 298.15 K P2= 1.052E-3 mmHg

From the Clausius Clapeyron:

ln(0.8045 mmHg/1.052E-3 mmHg)= ΔH/R*(1/298.15 K - 1/392.7 K)

ΔH/R = 8221.89 K-1
ΔH = 68361 J/mol

ΔH/T = ΔS = 68361/298.15 = 229.29 J/mol K

However the answer is 350.60 J/mol K.

I tried adding the ΔSvap to the derived value (229.29+117.2) , however that only gives me 346.5 J/mol K
 
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  • #2
Maybe this relation might be helpful: ##L = T\Delta S = T(S_2 - S_1)##.
 
  • #3
I would use L= TΔS = 68361 J/mol = 229.29 J/mol K x 392.7 K
= 392.7(S2-S1),
At this point I am unsure what to use for S2 to solve for S1 or vice versa.
 

1. What is the significance of the Standard Entropy of a liquid at melting point with no S(298.15) given?

The Standard Entropy of a liquid at melting point with no S(298.15) given is a measure of the amount of disorder or randomness in a liquid at its melting point when there is no additional heat or energy added. It helps to determine the stability and behavior of the liquid at its melting point.

2. How is the Standard Entropy of a liquid at melting point with no S(298.15) given calculated?

The Standard Entropy of a liquid at melting point with no S(298.15) given is calculated using the formula ΔS = ΔH/T, where ΔS is the change in entropy, ΔH is the change in enthalpy, and T is the temperature in Kelvin.

3. What is the unit of measurement for the Standard Entropy of a liquid at melting point with no S(298.15) given?

The unit of measurement for the Standard Entropy of a liquid at melting point with no S(298.15) given is Joules per mole-Kelvin (J/mol-K).

4. How does the Standard Entropy of a liquid at melting point with no S(298.15) given affect the physical properties of the liquid?

The Standard Entropy of a liquid at melting point with no S(298.15) given affects the physical properties of the liquid by influencing its melting point, boiling point, and overall stability. A higher Standard Entropy indicates a more disordered or less stable liquid at its melting point.

5. Can the Standard Entropy of a liquid at melting point with no S(298.15) given change?

Yes, the Standard Entropy of a liquid at melting point with no S(298.15) given can change depending on factors such as pressure, temperature, and the addition of impurities. It is also affected by the phase transition from liquid to solid at the melting point.

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