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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?

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Climb the stairs E Q=mC(T f -T 0 ) Q=mH f Q=mH v

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Heat water from Ice to Vapor (A) First heat to melting point, 24.0 x 2.108 x (0- -10)= 506 (B) Then melt the ice, 24.0 x 334= 8016 (C) Then heat to boiling, 24.0 x 4.186 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 1.996 x (120-100)= 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

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H of Reaction SubstanceHeat of formation (kJ/mol) C 2 H 4 52.30 O 2 0 CO 2 -393.51 H 2 O-285.85 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 52.30 +3 x 0 → 2 x (-393.51) + 2 x (-285.85) +52.30 + 0 → -787.02-571.70 +52.30(reactants) → -1358.72(products) -52.30 (subtract reactant’s H) -1411.02 kJ (total for reaction)

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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.

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