How many joules are needed to change 120.g of water at 20.0C to steam at 100.0C? How many joules of energy must be removed from 126 g of water at 240C to form ice at 0.0C? How many joules are required to change 225 g of ice at -15. oC to steam at 140. oC ?

How many joules are needed to change 120.g of water at 20.0C to steam at 100.0C? First heat H2O from 20.0C to boiling (1000C): Heat = 120.g x 80.0C x 4.18 J/g0C = 40128 J = 40.1 kJ Then find heat to vaporize the water: Heat = 120.g x 2260 J/g = 271200 J = 271 kJ Total heat = 311 kJ

How many joules of energy must be removed from 126 g of water at 240C to form ice at 00C? First cool water from 240C to 00C: Heat = 126g x 240C x 4.18 J/g0C = 12640 J (12.6 kJ) = 13 kJ Then find heat removed to freeze H2O: Heat = 126 g x 335 J/g = 42210 J = 42.2 kJ Total heat = 55 kJ (54.8)

How many joules are required to change 225 g of ice at -15. oC to steam at 140. oC? First heat the solid (-15. oC) to melting point(00C) : Heat = 225g x 15.oC x 2.03 J/g oC = 6851 J = 6.9 kJ Then melt the ice: Heat = 225 g x 335 J/g = 75375 J = 75.4 kJ Then heat the ice water(0.0C) to boiling(100.0C): Heat = 225 g x 100.0C x 4.18 J/g0C = 94050 J = 94.1 kJ Then, find heat to vaporize the H2O: Heat = 225 g x 2259 J/g = 508275 J = (508.3) = 508 kJ Finally, heat the gas (100. oC) to 1400C) : Heat = 225g x 40.oC x 2.01 J/g oC =18090 J = 18 kJ Total heat = 702 kJ