Chemical Reactions Links

Chemical Reactions

Simple Thermodynamics

Chemical Bonding

Endothermic Reactions (Fun activity)

Exothermic Reactions (Fun Activity)

Endothermic Reactions

Endo just means within and thermic just means heat - so what we have there is a reaction that takes in, or absorbs, heat. That is pretty much it! If a chemical reaction takes in heat it is called endothermic.

This can be nicely illustrated to kids by doing the really fun hands-on-activity of making ice cream in a baggie.

I know - that is nothing new. In fact, we've all done it before, I'm sure. But was it ever properly explained to you?

I see this little experiment all over the web but few websites even mention that the reaction is endothermic, some say the obvious (the salt lowers the temperature) and most say nothing at all about the chemistry involved.

But we're homeschoolers - so we must know these things!

So, here it is - the Ice Cream in a Baggie Experiment with all the gory science details no one else cares about...

Ingredients

1/2 cup milk

1/2 cup whipping cream (heavy cream)

1/4 cup sugar

1/4 teaspoon vanilla or other flavoring (we used orange!)

1/2 to 3/4 cup Ice Cream Salt (Rock Salt)

2 cups ice

1-quart baggie

1-gallon baggie

Add Milk to small baggies

Add Cream to same baggie

Add Sugar to same baggie

What you get here is a nice little density experiment! But that is for another time - just enjoy the pretty layers....

Add vanilla or other flavoring...

...and food coloring if desired.

We wanted more than just one serving...just make sure each baggie has its own serving.

Add ice to large baggie...

...and salt.

Put smaller baggies inside the larger one - make sure the smaller baggies are sealed tight! Then shake-shake-shake! For about 10 minutes....

...and Voila! Ice cream in a baggie!

The Science of Ice Cream in a Baggie

This is an endothermic reaction - for the ingredients to freeze heat must be transferred.

Heat can only go from a hotter substance to a cooler substance.

In this reaction heat is travelling from your hands (shaking) and the ingredients to the ice/salt mixture.

Melting occurs when the heat is transferred from your hands and the baggie - (this makes the ice melt)

Freezing occurs when the ice is added to the mixture - (this makes the ice cream mixture freeze)

When the rate of freezing is the same as the rate of melting, the amount of ice and the amount of water won't change. The ice and water are said to be in dynamic equilibrium with each other

Water freezes at 0 degrees Celsius

Salt LOWERS the freezing temperature of water to -21.1 degrees Celsius

This means that the ice and salt mixture must get even more heat from somewhere in order to melt.

Remember the First Law of Thermodynamics which states: Heat can only be transferred from a hotter substance to a colder substance. The heat is LEAVING the ice cream mixture at a faster rate with salt and ice, than with just ice alone.

Links to Student Help pages:

Chemical Reactions
Simple Thermodynamics
Chemical Bonding
Endothermic Reactions (Fun activity)
Exothermic Reactions (Fun Activity)
Astronomy for Kids
How to Use a Sky Map
Planetarium Software
Astronomy Unit Study/Activities
What is Molecular Biology
Mendelian Genetics
Molecular Genetics
DNA Replication
DNA Replication Enzymes
DNA Replication Mechanism
What is Cell Biology
Cellular Components
The Endomembrane System
Golgi Apparatus
Vesicles and Cellular Transport
The Mitochondria
The Plasma Membrane
Plant Biology
Photosynthesis
Parts of a Plant
Plant Life Cycle 1
Plant Life Cycle 2
Cell Cycle
Cell Cycle Mitosis
Cell Cycle Control