Calorimetry

Calorimetry is a way scientific expriment to figure the energy released or absorbed by a reaction. In calaorimetry, we use a calorimeter, that is composed by a system (chemical reaction) and surroundings (water or something like water).  When the reaction measures a made. and the asusmpition the THERMAL ENERGY CHANGE IS EQUAL TO THE CHANGE IN ENTHALPY, SINCE THE ENERGY LOST OR GAINED BY THE SYSTEM IS EQUAL TO THE ENERGY GAINED OR LOST BY THE SURROUNDINGS.
Don;t forget that when the question gives you the mass of the calorimeter, and its a metal. You must account it as one of the surroundings, which means that not only water is present.