Aqua

 

 

National Aeronautics and

Space Administration

 

 

Goddard Space Flight Center


 

 

 


Aqua background information

FOR THE CLASSROOM†††††††

Conservation of Energy and Phase Change of Water

Adapted from the Institute for Global Environmental Strategies

http://www.strategies.org

 

INTRODUCTION

Water is the primary energy mover on Earth. Waterís high specific heat allows it to transport energy (in the form of heat) in the Earthís atmosphere and oceans. Both liquid water and water vapor can transport energy over great distances, for instance through ocean currents and winds. In this exercise, we look at the energy absorbed by water needed to produce phase changes from ice to liquid.

 

MATERIALS

Bunsen burner; ring stand with wire screen; ring; 250 mL beaker; goggles; beaker tongs; pencil & paper; graph paper; thermometer; stopwatch; plastic stirrer; ice; water.

 

PROCEDURE

  1. Attach the ring to the ring stand and place the Bunsen burner under the center of the ring. Adjust the ring so itís 3-5 cm above the top of the Bunsen burner and place the wire screen on top of the ring.
  2. Put your goggles on. Take the Bunsen burner out from under the wire screen and light the burner when directed to do so by your instructor. Adjust the gas so that you have a small flame. Adjust the air holes until the flame is no longer yellow in color.
  3. Put 150 mL of ice in the beaker and add 50 mL of water.
  4. Using the plastic stirrer, stir the water and ice mixture. When it reaches the lowest temperature, record the temperature on the chart.
  5. Using beaker tongs, place the beaker on the ring stand and start the stopwatch simultaneously. Begin recording the temperature every 30 seconds for at least 15 minutes. Continuously stir the ice/water mixture.
  6. Note the time when the ice begins to melt, when all the ice is gone, and when the water begins to boil.
  7. Graph the data placing the temperature on the vertical axis and the time on the horizontal axis. Mark the points where the water was changing phase.

 

QUESTIONS

  1. According to your graph, did the temperature change during the phase changes?
  2. When was the temperature change most rapid? (Refer to the slope of your graph.) If the Bunsen burner output was constant, what can you infer about the absorption of energy by the water?
  3. Which phase change required to most energy to achieve?
  4. What can you infer about the release of energy by the water when it reverses the direction of phase change? (Vapor to liquid to solid)

 

Image rendered by Reto Stockli, based on a prior image by TRW. Text by C. Parkinson, Aqua Project Scientist, Goddard Space Flight Center.