Complete the Journey From Home: Fun Experiment!

Chapter Listing

Now that you've completed your journey to the Clapeyron-Clausius Equation, let's see how it can be applied in an experiment.

Pressure cookers use high pressures to increase the boiling point of water, this means that the steam that cooks the food inside the pressure cooker is hotter than 100°C, which isn't possible at atmospheric pressure. This means food can be cooked much more quickly.

Apparatus:

Pressure cooker with pressure and temperature gauge

Hot plate ( if pressure cooker is not electric )

Method

1. Fill pressure cooker half full of water and lock the lid in place

2. Set pressure cooker valve to the low pressure setting

3. Place pressure cooker on hot plate and heat until continuous vapour releases from valve and temperature and pressure is constant

4. Record the temperature on the thermometer and the pressure on the gauge

5. Release the pressure from the pressure cooker using the valve, being careful not to place your hand in the escaping vapour

6. Set pressure cooker valve to high pressure setting

7. Repeat steps 3-5

The Clapeyron-Clausius equation can now be used to estimate the heat of vapourisation of water.

Substitute the pressure and temperatures found in step 4 for P1 and T1 respectively as well as those in step 7 for P2 and T2 respectively. From there the equation can be re-arranged to give the heat of vapourisation:

Some Questions to Think About

If more readings could be taken, a graph could be constructed of (1/T1 - 1/T2) against ln(P2/P1) , what would the gradient of the line of best fit equate to?

What are some sources of inaccuracy in this experiment?

(ie. Is all of the heat transferred evenly across the pressure cooker?, How accurate are the measurement apparatus?, Could the apparatus be modified to give a more accurate result?)

What assumptions have been made in the theory of this experiment?