Taku Glacier Ice Berg in Stephens Passage near Juneau, AK. Photo C.Good
ENGAGE
Phun Physics of Phase Change - BLAB...
Let's revisit our physics lesson a few modules back when we explored how thermal energy is transferred when water changes phase. However, in this case we are talking about the latent heat of fusion, or heat energy exchange that occurs when freezing or thawing water.
Unlike the latent heat of vaporization of water (540 cal/g), the latent heat of fusion for water comes in around 80 calories per gram.
That is, 1 gram of solid water (ice) at 0 degrees Celsius requires an additional 80 calories of thermal energy to become 1 gram of liquid water at the same temperature. Which is to say, like evaporation, thawing is a cooling process. That's why we put ice in our beverages.
And just like the condensation process described earlier, freezing is a warming process. This may sound strange, but water freezing in the arctic helps to warm the surrounding air as the water releases 80 calories of thermal energy per gram into its immediate environment. Crazy.
EXPLORE
Phun Physics of Phase Change - LABS!
Whats more phun than watching paint dry or grass grow? To thrill even the most bored video game enthusiast in the class, try watching ice melt!
Try This Trick!
- Safety First! Glass, Heat, Water, Electricity Hazards
- Partially fill a heat resistant glass container with ice-water.
- Use a safety thermometer (no mercury) to gently stir the ice-water while pausing to check and record the temperature once a minute for several (5-10) minutes.
- Now place the vessel on a safe heat source and continue gently stirring and taking the temperature for a few minutes.
Review this graph demonstrating the flow of thermal energy in water as it melts and warms.
Click on Graph to EnlargeEXPLAIN
- What is happening to the water's temperature as the ice melts?
- What is happening to the temperature as the rate of heating increases?
- What happens to the temperature of the water after the ice melts?
- Where is the increased thermal energy you are putting into the container going?
EXTEND
- What does this experiment tell you about the role of ice on Earth and what is likely to happen when all the sea ice melts?
- How does this simple experiment inform you or your students about the role of sea ice in regulating our planets climate?
EXPLORE SOME MORE...
Try This Trick!
- Safety First! Glass, Water Hazards
- Partially fill an appropriate container with ice-water.
- Use a safety thermometer (no mercury) to gently stir the ice-water while pausing to check and record the temperature once a minute for several (3-5) minutes.
- Next, slowly add a small quantity of salt to the ice water and continue to record the temperature while gently stirring for a few more minutes.
EXPLAIN
- What is happening to the water's temperature as the ice melts before and after adding salt?
- How and why does the temperature change?
- How does this lab relate to climate and sea ice?
EXTEND
- What does a graph of this data look like?
- Try making old-fashioned home-made ice-cream to demonstrate the super-cooling affects of salt.
EVALUATE
- How does this simple experiment inform you or your students about the role of sea ice in regulating our planets climate?
Helpful Hint: For a Native American view on related activities, see
Keepers of the Earth: Native American Stories and Environmental Activities for Children, found in Google Books.
Keepers of the Earth: Native American Stories and Environmental Activities for Children, found in Google Books.
