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Freezer Flask Demonstration
Recommended Grade Level(s):
Appropriate for: Middle school and High school
Time Requirements:
Activity Time: 30 minutes
Teaching Topics & Concepts:
• To illustrate an endothermic reaction involving reactants in the solid state.
• Structure and properties of matter, interactions of energy and matter.
• Enthalpy, entropy, and free energy.
• Chemical reactions
• Analyzing and interpreting data
Background:
Endothermic reactions suck—they suck up the heat from their surroundings. Con-
sider the handy cold packs we use for first aid. These packs consist of two bags: one
containing water, inside a bag containing ammonium nitrate, calcium ammonium
nitrate, or urea. When the inner bag of water is broken by squeezing the package, it dissolves the solid in an endothermic process.
This entropy-driven reaction takes heat from the surroundings—just sucks the heat right up. Studying the science behind endo-
thermic reactions will help students understand why NH4NO3(s)+ΔH2O—>NH
+
4+NO-3 brings so much relief to a sprained ankle.
Use this Freezer Flask activity to demonstrate an even colder reaction!
Materials:
• Barium hydroxide 8—hydrate, Ba(OH)2-8H20
• Ammonium thiocyanate, NH4SCN
• 500 mL Erlenmeyer flask with rubber stopper
• Wood board
• Electronic balance
• Water
+
ward
'
s
science
Safety
• Read the SDS sheets for all chemicals before using them.
• Ammonia gas is produced. Avoid inhalation. (You may wish to do this demonstration in a fume hood.)
• Wear safety glasses, gloves, and a lab coat.
• Firmly hold the rubber stopper to prevent it from popping off.
• Do not drink the contents of the flask. Avoid skin contact. If you get any solution on your skin,
rinse it off with water.
!
