Which term describes a reaction that absorbs heat from its surroundings?

• A. Endothermic
• B. Exothermic
• C. Isothermal
• D. Runaway

Answer: (A)

A reaction that absorbs heat from its surroundings is endothermic. In an endothermic process, the system takes in energy from outside, so heat flows from the surroundings into the reacting chemicals and the surroundings often feel cooler. An everyday example is the dissolution of ammonium nitrate in water. By contrast, an exothermic reaction releases heat to the surroundings, which can raise the surrounding temperature. Isothermal describes a process where the temperature stays constant, which can occur with heat flow balancing everything but doesn’t specify the direction of heat. Runaway refers to a dangerous situation where heat is generated faster than it can be removed, causing a rapid temperature rise, not simply heat absorption from the surroundings.