2-3-2011 Lecture Notes

# 2-3-2011 Lecture Notes - Entropy is never zero at any...

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Entropy is never zero at any temperature above 0 K Absolute entropy depends on the phase of the substance I 2 - solid - 116 J/mol K Bl 2 - liquid - 152 J/mol K Cl 2 - gas - 233 J/mol K If substances have the same phase and similar structure, entropy increases with molar mass Cu (s) - 63.6 g/mol – 33 J/mol K Ag (s) - 108 g/mol – 43 J/mol K Entropy increases as size/complexity of a molecule increases - Molecules with more atoms have more ways to vibrate, more ways to disperse their energy Standard Entropy of Reaction can often predict the sign of standard entropy of reaction - Major change change in # of moles of gas , predicts that entropy will increase becaus moles of gas increases or decrease because moles of gas decreases Calculating the entropy of reaction - Apply Hess’s Law (S, state function) combine S values (appendix B) to find entropy of reaction - Look up values of S for each molecule - ∆S react = ∑mS prod - ∑nS react Spontaneity is affected by both enthalpy and entropy -

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