Change of State

At what temperature does water freeze? Melt? Boil? You probably know the answer already, but do you know what happens in between? How much energy (heat) does it take to cause these changes? In this lab you will investigate how much heat it takes to change a solid into a liquid and a liquid into a gas.

Heat is a measure of the energy put into a system. Heat is also a measure of how much energy a system can hold. The amount of energy a substance can hold depends upon the arrangement of its molecules. Have you ever heard of a calorie? A calorie is a measure of heat! A calorie is the amount of energy it takes to raise 1 gram of water by 1 oC.

Create a data table that will show the rise of temperature over a period of time. You will need quite a few rows!

Materials:

Hot plateRing Stand and clamp

ThermometerHalf of a stopper

Beaker

Balance

Ice

Procedure:

  1. Fill a beaker half way full of ice and quickly find the mass of the ice. (Remember: you need to take the mass of the empty beaker first!)
  1. Before you continue, predict how many calories you think it will take to melt the ice and boil the water. (Hint: a good prediction can be made mathematically if you know the melting and boiling points of water!)
  1. Place the thermometer in the clamp with a half of a stopper. Place the thermometer in the beaker so that it doesn’t touch the bottom of the beaker and begin reading the temperature. Take a temperature reading every minute until all of the ice is melted.
  1. Turn the hot plate on LOW. (Yellow – 5 Gray – 4)
  1. After all of the ice has melted turn the hot plate to high.
  1. Take temperature readings every minute until the water begins to boil (vigorously) and record them in the data table.
  1. Continue to take temperature readings every minute for five minutes after the water begins to boil.
  1. Turn off your hot plate and let the beaker cool.

Results:

Now create a time versus temperature graph using your data.

Knowing that it takes 1 calorie to raise 1 g of water 1 oC, calculate the amount of heat put into your sample for the total temperature increase. (Example: I had 100g of water. The temperature rose 10 degrees C, so 1000 calories were needed.)

Write a conclusion about the total amount of heat required to change water from its solid state to its gas state.

Answer the following questions:

  1. Define the Heat of Fusion:
  1. Define the Heat of Vaporization:
  1. Label these points on your graph:
  1. How much energy did it take to melt the ice?
  1. How much energy was required to make the water boil?
  1. Was there a place in which the temperature quit rising for a period of time?
  1. At which temperature did this take place?
  1. Is energy still being added even though the temperature is not rising?
  1. Where is the energy going?