Evaporation and Condensation II

Objectives

• Investigate factors affecting the rate of evaporation.

• Compare the cooling effect produced as the rate of evaporation is altered.

• Be able to describe and explain processes involving evaporation and condensation, and compare different scenarios in terms of the rate of evaporation.

Task 1 - Recap

The particles in a liquid have a range of energies.  Remind the person next to you:

• Why some particles end up with more energy than others.

• How the average thermal energy is connected to the temperature.

• How this leads to the process of evaporation.

Task 2

We are going to wrap two thermometers in cotton wool which has been soaked in propanone, and monitor their temperatures for 5 minutes.  We will place one thermometer in front of a desk fan.

Which thermometer will cool down more rapidly?  Why do you think this is?  Write a prediction what you think will happen and why, giving as many scientific reasons as you can.

When you have finished copy the table below into your book to record your results:

Work out the temperature decrease of each thermometer.  Which thermometer cooled more rapidly?  Write a few sentences to explain what you found, and explain why it happened.

Task 3

Use your understanding of evaporation to answer these questions:

1. Look at these saucepans. How will evaporation affect how quickly the contents of the saucepans will heat up?
2. Look at these clothes on the washing line. Which clothes will dry quickest and why?
3. Look at the window behind this cooker. Can you explain why the glass is covered with condensation?

There is a support sheet here to help with question 3, if required.