How much heat is released when 250.0 g of water cools from 80.0 °C to 60.0 °C? (c = 4.18 J/(g·°C))

Core Concept

Take ΔT = 60.0 - 80.0 = -20.0 °C and apply q = mcΔT: q = 250.0 g × 4.18 J/(g·°C) × (-20.0 °C) = -20,900 J, which is -20.9 kJ. The negative sign appears automatically because the water's temperature fell. A falling temperature means the water releases heat to its surroundings. Dropping the sign would falsely report the water as absorbing energy.