The Heat Solution

Author(s): Jim Schwagle, Laurie Aiello
Instrumentation - Teacher's Guide
SED 695B; Fall 2005


This device shows how a liquid solution, when activated by the physical bending of a metal disk can induce crystals to form and consequently release a large amount of heat.


Topics addressed:

  • Potential Energy
  • Supersaturated Solutions
  • Energy Transfer
  • Specific Heat
  • Entropy


High School Physics

3a. Students know heat flow and work are two forms of energy transfer between systems.
3c. Students know the internal energy of an object includes the energy of random motion of the object’s atoms and molecules, often referred to as thermal energy. The greater the temperature of the object, the greater the energy of motion of the atoms and molecules that make up the object.
3d. Students know that most processes tend to decrease the order of a system over time and that energy levels are eventually distributed uniformly.
3e. Students know that entropy is a quantity that measures the order or disorder of a system and that this quantity is larger for a more disordered system.
3f.* Students know the statement “Entropy tends to increase” is a law of statistical probability that governs all closed systems (second law of thermodynamics).

High School Chemistry

6a. Students know the definitions of solute and solvent.




Demonstration Video:

As the metal disk is flexed the supersaturated solution of sodium acetate is induced into forming crystals that in turn releases considerable stored energy in the form of heat, with the attending rise in temperature..


  • Ensure that the solution is completely saturated by placing the pouch in boiling water until the crystals have dissolved.
  • Allow the pouch to cool to room temperature. The pouch will remain liquid as long as the crystals have not been "activated".
  • Bend the metal disk inside the pouch and crystals will immediately begin to form along with the heating of the pouch to a temperature of approximately 130 Fahrenheit.


  • The pouch must be placed in boiling water to dissolve the crystals so care must be taken when removing it.
  • As the crystals form the pouch heats up quickly to a high temperature. Care must be taken to reduce the risk of burns by handling the pouch as little as possible.


  1. In what form is the energy stored in the super-saturated solution? Potential Energy
  2. A change of state is what kind of change (physical/chemical)? Physical Change
  3. What other devices are used for energy storage? Batteries (chemical), springs, dams (potential energy of water)
  4. If the pouch is removed from the boiling water before all crystals have dissolved, what will happen to the liquid in the pouch as it cools? The crystals will reform as the solution cools since there is already a "seed" crystal to induce formation.
  5. A super-saturated solution contains more/less solute than can normally be dissolved in the solvent? More


The same process can be illustrated by pouring the solution onto a "seed" crystal, that starts the crystallization process. Heat is radiated from the solid.

As the solution crystallizes, energy is released from it as shown by the considerable increase in temperature.

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