Final answer:
In calorimetry, heat transfers from the hot metal to the cool water until thermal equilibrium is reached, with the metal losing heat and the water gaining it.
Step-by-step explanation:
In the context of calorimetry, when a hot metal is placed in cool water within a calorimeter, the metal loses heat while the water gains it. This process continues until thermal equilibrium is reached, meaning both substances have the same temperature. The calorimeter is designed to prevent heat exchange with the environment; hence all heat transfer is contained within the system, leading to a net heat change of zero. An exothermic reaction will cause the temperature of the water to rise as the reaction releases heat, while an endothermic reaction will result in a temperature decrease as heat is absorbed from the surroundings into the system.