Presentation on theme: "Heat of Fusion and Vaporization Water H f = 334 J/g Water H v =2,270 J/g The specific heat of a substance depends on its state. Solid water Cp =2.108 J/g."— Presentation transcript:
Heat of Fusion and Vaporization Water H f = 334 J/g Water H v =2,270 J/g The specific heat of a substance depends on its state. Solid water Cp =2.108 J/g o C Liquid water Cp =4.186 J/g o C Water vapor Cp =1.996 J/g o C So how much energy is required to heat 24.0 g of water from ice at -10 o C to vapor at 120 o C?
Climb the stairs E Q=mC(T f -T 0 ) Q=mH f Q=mH v
Heat water from Ice to Vapor (A) First heat to melting point, 24.0 x x (0- -10)= 506 (B) Then melt the ice, 24.0 x 334= 8016 (C) Then heat to boiling, 24.0 x x (100-0)=10046 (D) Then boil the water, 24.0 x 2270=54480 (E) Then heat the vapor to 120 o 24.0 x x ( )= 958 =74006 J or 74 kJ Steps m x C x (T f -T 0 ) = Q m x H f = Q m x H v = Q
H of Reaction SubstanceHeat of formation (kJ/mol) C 2 H O 2 0 CO H 2 O With these values we can determine the heat released in the reaction: C 2 H 4 + 3O 2 → 2CO 2 +2H 2 O ReactantsProducts 1 x x 0 → 2 x ( ) + 2 x ( ) → (reactants) → (products) (subtract reactant’s H) kJ (total for reaction)
Entropy Entropy is a measure of the disorder of a system. Matter tends to disorder. Reactions that release energy (exothermic, - H reaction) and produce more total mols of products than existed as reactants are said to be increasing entropy. Such reactions can be spontaneous. NaOH (s) Na + (aq) + OH - (aq) + heat There are twice the number of moles on the product side and it releases heat (feels warm). Entropy increases.