Fast Freeze Experiment. An Endothermic Reaction.
Preface to understand the process...
When chemical bonds are formed in creating a product, energy is released. In chemical reactions, energy must be added to break the bonds that hold molecules together. If the amount of energy needed to break bonds is more than the energy released when new bonds form, energy must be absorbed from the surroundings. This is called an ENDOTHERMIC reaction and results in a decrease in temperature. (when energy flows OUT of a reaction and raises the temperature of the surroundings, the reaction is EXOTHERMIC.) When barium hydroxide reacts with solid ammonium thiocyanate this endothermic reaction reduces the temperature to -20C or -30C.
What to do...
- Put a few drops of water on a small piece of wood (or cardboard), place the beaker on top.
- Pour barium hydroxide into the beaker followed by the ammonium thiocyanate
- Stir mixture.
NOTE: odor of AMMONIA becomes evident in about 30 seconds. If you hold a piece of dampened litmus over the beaker, a color change will occur showing the gas is basic.
- Liquid is produced and will freeze into a slush as the reaction proceeds.
- While performing the process, the beaker will freeze to the wood.
- Pick up the beaker, now frozen to the wood.