Cooling Paraffin wax

This investigation aims to show that the internal energy of a substance can change without a subsequent change in temperature.

It also aims to produce a cooling curve that illustrates the concept of latent heat.

You will need the following equipment:

• • large test tube containing about 2–3 cm depth of paraffin wax

  • Water bath or...

  • Beaker of iced water

  • Vernier temperature probe, change the sample rate to every 5 seconds

Place some solid paraffin wax into a large test tube. Heat the test tube in a water bath until the temperature of the paraffin wax is about 80 °C.

Remove the test tube from the water bath and place it in the iced water. Start recording the temperature of the paraffin as it falls until the temperature has fallen to about 30 °C. Gently and carefully stir with the thermometer while the liquid paraffin is cooling until it becomes clear the paraffin has set.

• 1. Download the data as a .csv and open it in excel. Draw a scatter plot of temp vs time.

  2. What causes the decrease in temperature of the liquid paraffin?

  3. How does the rate of cooling change as the liquid paraffin solidifies?

  4. During the process of solidification, what form of internal energy is being lost from the paraffin? Where is it going?

  5. What is the meaning of the term ‘latent heat of fusion’ and how does it relate to this investigation?

  6. Why is the rate of cooling so different for the liquid paraffin to the solid?

  7. Find temperature at which the latent heat of fusion for paraffin wax occurs from your graph, how does this compare to known values?

  8. What data do you need to calculate the latent heat of fusion for paraffin? Can you design an experiment which could do this?

Conclusion

Make a concluding statement that links your results to the content under study.

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