Temperature ( o C) Heat (J) Solid Liquid Gas Heat = mass x ΔT x C l Heat = mass x H Fusion Heat = mass x H Vaporization s ↔ l l ↔ g H Vaporization H Fusion M pt B pt Heat = mass x ΔT x C g Heat = mass x ΔT x C s Phase-Change Diagram H vap = - ∆ H cond H fus = - ∆ H solid Condensation pt Freezing pt

Heat of Fusion - energy required to change 1 gram of a solid into a liquid at its melting point. Water ( ∆ H fus ) = 335 J / g Heat of Vaporization - energy required to change 1 gram of a liquid into a gas at its normal boiling point. Water (C l ) = 4.18 J / g o C Water ( ∆ H vap ) = 2260 J / g Specific Heat - energy required to change the temperature of 1 gram of a substance by 1 o C. C g = 2.01 J / g o C C s = 2.03 J / g o C = - ∆ H cond = - ∆ H solid

Temperature ( o C) 1) Heat = mass x ΔT x C p 2) Heat = mass x H V s ↔ l l ↔ g Heat (J) = 50.0 g x 18.4 o C x J/g o C = 1,970 J = 50.0 g x 855 J/g= 42,800 J _________ 44,800 J X X 78.4 o C 50.0 g ethyl 60.0 o C → 78.4 o C o C or 44.8 kJ Practice

How many Joules of energy would be liberated by condensing 50.0 mol of steam at o C and allowing the liquid to cool to 30.0 o C?

Temperature ( o C) 1) Condense: Heat removed = mass x H V 2) Cool: Heat removed = mass x ΔT x C l s ↔ l l ↔ g Heat (J) = 900. g x 2260 J/g = 2030 kJ = 263 kJ _________ 2290 kJ X X o C o C 50.0 mol x 18.0 g = 900. g H 2 O 1 mol = 900. g x 70.0 o C x 4.18 J/g o C