Chapter Five: The Clapeyron-Clausius Equation

Chapter Listing

Home: Journey to the Clapeyron-Clausius Equation

Chapter One: The Gibbs Equation

Chapter Two: The Tds Equation

Chapter Three: The Maxwell Relations

Chapter Four: The Clapeyron Equation

Chapter Five: The Clapeyron-Clausius Equation

Experiment: Complete the Journey From Home: Fun Experiment!

Real World Applications: The Sky's the Limit with the Clapeyron-Clausius Equation

References: References

HELP GO BACK! - Chapter Four: The Clapeyron Equation

Clapeyron - Clausius Equation

Using what we have found in previous sections and some approximations, we can find the Clapeyron- Clausius equation.

Why is this useful? 

It allows you to work out how saturation pressure changes with temperature.

Two key assumptions must be made and because of this, the equation is actually an approximation rather than a definite result. These assumptions are:

1) The vapor must be treated as an ideal gas. This means that   

ν2 = RT/P

2) At low pressures, the lower value for specific volume can be ignored.  

ν12 >> ν1    so  ν12 = ν2

These can be substituted into the Clapeyron equation found in the previous section to give

Then, rearranging by moving the T's and P's to the same side, we get

Due to the fact we have P and T on opposing sides, we can integrate each side. This gives us the final equation.

In the equation, R = Universal gas constant, T = temperature (in Kelvin), P = pressure, h = enthalpy. 

If you are not sure about any of these properties, you will be able to find more information on what they are on other pages on the allaboutthermofluids.com website.

Congratulations.

You have reached the end of your journey. But in order to make sure you have understood the journey, you must now complete the quiz.

THE QUIZ