From the change of free enthalpy or Gibbs energy, it is possible to see whether a chemical reaction can take place spontaneously. It includes the change in the enthalpy of reaction ΔH and the entropy change ΔS, depending on the temperature T: ΔG = ΔH -T · ΔS. A reaction occurs when ΔG is negative. For endothermic reactions, the term T·ΔS needs to be large enough for this to happen. Consequently, in an endothermic reaction, the disorder must become larger for the reaction to take place. In this experiment, the students perform an endothermic reaction in which the disorder obviously becomes larger. The students learn to estimate the entropy, i.e. the disorder, using the reaction equation and, along the way, learn about a reaction that cools down significantly.
