The document discusses heat of precipitation, which is the energy change that occurs when one mole of precipitate is formed from its ions in a precipitation reaction. As an example, it states that the precipitation reaction of lead nitrate and sodium sulfate forming lead sulfate and sodium nitrate releases -50.4 kJ of energy per mole of lead sulfate formed. It also provides methods for calculating the heat released when different amounts of lead sulfate are formed using the heat of precipitation value.