Chapter%207

# Chapter%207 - 7.32(a increases Generally entropy increases...

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Unformatted text preview: 7.32 (a) increases. Generally, entropy increases when a solid is dissolved because the molecules or ions are dispersed in the solvent, giving them more locations over which to arrange themselves. (b) decreases. In this example, twelve moles of reactants form seven moles of products, so we might expect immediately that entropy would decrease; however, we must also consider the states of the various reactants and products. There are six moles of gas on each side of the equation so this might roughly balance; however, we still expect a decrease in entropy for the gases because CO 2 (g) (a triatomic molecule) is more complex than O 2 (a diatomic molecule). The remainder of the reaction is six moles of liquid going to one mole of solid, which again would predict a decrease in overall entropy. (c) In the evaporation of water, a liquid is converted to a gas, which should be accompanied by an increase in entropy. 7.40 For C 2 H 5 OH, the molar enthalpy of vaporization is found by dividing the amount of energy supplied to cause the phase transition by the number of moles of C 2 H 5 O that underwent the transition: ( ) ( ) 1 1 1 1 500 J s (4.0 min) 60 s min 43 kJ mol 400.15 g 271.15 g 46.07 g mol vap H − − − − ⋅ ⋅ Δ = = ⋅ − ⋅ The associated change in entropy is then found using: 1 1 1 43 kJ mol 120 J mol K 351.5 K − − − Δ ⋅ Δ = = = ⋅ ⋅ vap vap H S T For C 4 H 10 the enthalpy and entropy of vaporization are: ( ) ( ) 1 1 1 1 500 J s (4.0 min) 60 s min 22 kJ mol 398.05 g 74.95 g 58.123 g mol − − − − ⋅ ⋅ Δ = = ⋅ − ⋅ vap H 1-1 1 22 kJ mol 81 J mol K 273.2 K − − Δ ⋅ Δ = = = ⋅ ⋅ vap vap H S T For CH 4 O the enthalpy and entropy of vaporization are: ( ) ( ) 1 1 1 1 500 J s (4.0 min) 60 s min 38 kJ mol 395.15 g 294.25 g 32.042 g mol − − − − ⋅ ⋅ Δ = = ⋅ − ⋅...
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## This note was uploaded on 01/30/2012 for the course CHEM 6B taught by Professor Crowell during the Spring '08 term at UCSD.

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Chapter%207 - 7.32(a increases Generally entropy increases...

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