American Board of Surgical Assistants (ABSA) Orthopedic Practice Test

What reaction occurs when plaster of Paris rolls are dipped in water above 75°F?

1. Exothermic reaction

2. Endothermic reaction

3. Hydrolysis reaction

4. Exothermic and cooling reaction

The correct answer is: Exothermic reaction

When plaster of Paris rolls are dipped in water above 75°F, an exothermic reaction occurs. This type of reaction involves the release of heat as the plaster of Paris, which is calcium sulfate hemihydrate, reacts with water to form calcium sulfate dihydrate. The process of hydration results in the setting of the plaster, and as it hardens, heat is emitted into the surroundings. The increase in temperature is indicative of an exothermic process, as energy is released when chemical bonds are formed in the hydrated product. This is important to understand in a clinical setting, as the heat generated can affect the surrounding tissues and should be monitored to prevent discomfort or burns. In contrast, endothermic reactions absorb heat, leading to a drop in temperature, which is not the case here. A hydrolysis reaction particularly involves the reaction of a compound with water but does not specifically indicate an energy exchange like an exothermic reaction does. The option relating to an exothermic and cooling reaction misrepresents the nature of the process, as a cooling effect would not accompany the heat release in this scenario. Understanding that the reaction is exothermic provides insight into the chemistry involved in using plaster of Paris in orthopedic applications.