Burdge/Overby, Chemistry: Atoms First, 2e Ch14

SEC TION 14.3 ? Entropy Changes in a System E4 E8 Ar Kr E7 E3 E6 Molar Mass E5 E E2 581 E The energy levels for a substance with a larger molar mass are more closely spaced. Kr, for example, has roughly twice the molar mass of Ar. Thus, Kr has roughly twice as many energy levels within which the system’s energy can be dispersed. E4 E3 E1 E2 E1 E5 E3 E4 Phase Change Because of greater mobility, there are many more different possible arrangements (W ) of molecules in the liquid phase than there are in the solid phase; and there are many, many more different possible arrangements of molecules in the gas phase than there are in the liquid phase. Entropy of a substance increases when it is melted (s l), vaporized (l g), or sublimed (s g). N2O4(g) E2 E E3 E E2 E1 E1 2NO2(g) E4 E4 E3 E3 Chemical Reaction E E2 E1 E E2 When a chemical reaction produces more gas molecules than it consumes, the number of different possible arrangements of molecules (W ) increases and entropy increases. E1 What’s the point? Although several factors can influence the entropy of a system or the entropy change associated with a process, often one factor dominates the outcome. Each of these comparisons shows a qualitative illustration of one of the important factors. 581 bur11184_ch14_570-603.indd 581 9/10/13 12:01 PM

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