When 3.0 kg of water is cooled from 80.0C to 10.0C, how much heat energy is lost?

Answer 1

don't you have some handy formula for water with units of J/°K ?

Answer 2

Are you looking for
q = mass H2O x specific heat H2O x (Tfinal - Tintial)

Answer 3

the formula is 4.179