Final answer:
An endothermic reaction occurred when ammonia chloride was mixed with water, indicated by the temperature drop from 27 to 10 degrees Celsius as the reaction absorbs heat from the surroundings.
Step-by-step explanation:
When ammonia chloride is mixed with water and the temperature of the mixture decreases, as you observed from 27 degrees Celsius to 10 degrees Celsius, an endothermic reaction has occurred. This means that the reaction absorbs heat from the surroundings, causing the temperature of the solution to drop. When ammonium chloride dissolves in water, the dissolution process is endothermic, which is indicated by the temperature decrease.
Endothermic processes are those where the system absorbs heat, as opposed to exothermic processes where the system releases heat. An endothermic reaction often results in products that are less energetically stable than the reactants, but entropy or disorder of the system increases during the process. This can happen in various chemical processes such as the reaction of barium hydroxide with ammonium thiocyanate, which is known to be highly endothermic and can cause solutions to freeze.