# Lee/Kesler Correlation: Accuracy & Complexity

• gfd43tg
In summary, Lee/Kesler correlations are used as quick approximations for properties that are difficult to measure experimentally, while Redlich/Kwong equations are more accurate but require more complex calculations. The complexity of the equations for calculating residual enthalpy and entropy with RLK is due to the involvement of multiple independent variables and the need for numerous calculations.
gfd43tg
Gold Member
Hello,

I have been doing Lee/Kesler correlations ad nauseum to compare with calculated values for residual enthalpy and entropy with the Redlich/Kwong equation. My enthalpy values have varied as much as 400 J/mol with the correlation compared to the equation (enthalpy's in the 2500 J/mol range).

My question is why do I care about these Lee/Kesler correlations if they aren't even that accurate (assuming Redlich/Kwong is accurate) or vice versa if Lee/Kesler is accurate.

Also, why are these equations so horrendous for calculating the residual enthalpy and entropy with RLK? There is so much number crunching for it.

Last edited:
Thanks,Lee/Kesler correlations are used to approximate the properties of a substance that are not easily measured experimentally. They rely on a set of parameters (such as temperature and pressure) to approximate the behavior of the substance. Redlich/Kwong (RLK) equations are more accurate at predicting the thermal properties of a substance, but they require a more complex set of parameters to be calculated. The Lee/Kesler correlations are useful when you need a quick estimate of a property and don't have the time to calculate an exact value. However, they should not be used when an exact value is needed. In that case, the RLK equations should be used instead. In terms of why the equations are so complex for calculating the residual enthalpy and entropy with RLK, it is because the equations involve multiple independent variables and require a lot of calculations to determine the values.

## 1. What is the Lee/Kesler Correlation?

The Lee/Kesler Correlation is an empirical equation that is widely used in chemical engineering to estimate the vapor pressure and other thermodynamic properties of pure substances. It is based on a generalized compressibility factor and is applicable to a wide range of temperatures and pressures.

## 2. How accurate is the Lee/Kesler Correlation?

The accuracy of the Lee/Kesler Correlation depends on the specific substance being studied. In general, it is considered to be accurate within 5% for most substances. However, for some substances, the accuracy may be as high as 1%.

## 3. What factors affect the accuracy of the Lee/Kesler Correlation?

The accuracy of the Lee/Kesler Correlation is affected by the type of substance, temperature, and pressure. It is also influenced by the quality of the experimental data used to develop the correlation. Inaccurate or limited data can lead to less accurate results.

## 4. Is the Lee/Kesler Correlation complex to use?

The Lee/Kesler Correlation is considered to be a relatively complex equation, as it involves multiple parameters and calculations. However, with the use of modern software and calculators, it is relatively easy to use and does not require extensive mathematical knowledge.

## 5. Can the Lee/Kesler Correlation be used for mixtures?

No, the Lee/Kesler Correlation is only applicable to pure substances. For mixtures, a different correlation, such as the Peng-Robinson or Soave-Redlich-Kwong equations, should be used.

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