chap19_entropy&Gibbs

# typeiii endothermic hsys0andlessorder ssys0

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Unformatted text preview: CO2(g) = 213.74 J/mol•K C3H8(g) = 270.30 J/mol•K O2(g)= 205.07 J/mol•K • What is ∆ Suniv? 20 -∆H sys −(−2044kJ ) = +6.86 kJ K T 298 K ∆Srxn = [(4mol ×188.84 J ) + (3mol × 213.74 J ) − [1mol × 270.30 J ) + (5mol × 205.07 J )] = 1 00.93 J mol • K mol • K mol • K mol • K K ∆Suniv = ∆Ssurr + ∆Ssys = 6860 J + 100.93 J = 6961 J K K K ∆Ssurr = = 21 Spontaneous or not? 1 >0 Suniv>0 Exothermic More order <0 Endothermic Less order >0 4 Spontaneous <0 3 Less order <0 2 Exothermic >0 Endothermic More order >0 <0 Depends on H & S More favorable at lower temps Depends on H & S More favorable at higher temps Nonspontaneou s Suniver<0 22 Examples of each type • Type I – Exothermic (∆ Hsys<0) and less order (∆ Ssys>0) • Combustion reactions • Type IV C3H8(g) + 5O2(g) ⇒ 3CO2(g) + 4H2O(g) – Endothermic (∆ Hsys>0) and more order (∆ Ssys<0) N2(g) + 2H2(g) ⇒ N2H4(l) 23 Examples of each type (cont.) • Type II – Exothermic (∆ Hsys<0) and more order (∆ Ssys<0) • Temperature dependent – More favorable at lower temperatures N2(g) + 3H2(g) ⇒ 2NH3(g) 24 Examples of each type (cont.) • Type III – Endothermic (∆...
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