Standard Entropy for Liquid at Melting Point

In summary, the vapour pressures of a liquid have been measured and fit to an equation. The melting point has been determined and the standard entropy of the liquid at the melting point can be calculated using the Clausius Clapeyron equation. The calculated value is about half of the actual value, possibly due to additional variables such as the specific heat capacity and the entropy of vaporization of the liquid.
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Homework Statement


The vapour pressures of a liquid have been measured and fit to the following equation:
Log10 (mmHg) = -3571/T + 6.124
The melting point has been determined to be 392.7 K.
Calculate the standard entropy of the liquid at the melting point.


Homework Equations





The Attempt at a Solution

 
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  • #2
Where's your attempt?
 
  • #3
My attempt was as follows:
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(0.8045/1.052E-3)= ΔH/R*(1/298.15 K - 1/392.7 K)

ΔH/R = 8221.89
ΔH = 68361 J/mol

ΔH/T = ΔS = 68361/392.7 = 174.07 J/mol K

However the answer is about twice this value and a Cp value given for the liquid is 250 J/mol K and the entropy of vaporisation is 117 J/mol K (2 additonal variables)
 

1. What is standard entropy for liquid at melting point?

Standard entropy for liquid at melting point is a measure of the disorder or randomness of particles in a liquid state at its melting point. It is represented by the symbol S° and is measured in joules per mole-kelvin (J/mol·K).

2. How is standard entropy for liquid at melting point calculated?

Standard entropy for liquid at melting point is calculated using the following equation: 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 factors affect the standard entropy for liquid at melting point?

The standard entropy for liquid at melting point is affected by the molecular structure of the liquid, the strength of intermolecular forces, and the temperature at which the liquid is measured. It may also be influenced by the presence of impurities.

4. Why is standard entropy for liquid at melting point important?

Standard entropy for liquid at melting point plays a crucial role in understanding the thermodynamic properties of a substance. It helps in predicting the behavior of a liquid at its melting point, such as its heat capacity, phase transitions, and equilibrium conditions.

5. How does the standard entropy for liquid at melting point differ from that of a solid or gas?

The standard entropy for liquid at melting point is typically higher than that of a solid and lower than that of a gas. This is because the particles in a liquid have more freedom of movement compared to a solid, but less compared to a gas. Therefore, the disorder or randomness of particles is greater in a liquid than a solid, but less than a gas.

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