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Unformatted text preview: CH 4(g) + Cl 2(g) CH 3 Cl (g) + HCl (g) S o standard entropy 44.50 (cal/deg mol) 53.2 55.97 44.62 For the above reaction, the change in Standard Entropy is ! S o = " S o " S o products reactants ! S o = (55.97 + 44.62) - (44.50 + 53.2) cal/deg ! S o = +2.8 cal/deg mol At 25 o C (298 K), ! G o = ! H o- T ! S o = (-24.5 kcal/mol) - (298 deg)(2.8 cal/deg mol) ! G o =-24.5 kcal/mol - 0.834 kcal/mol = -25.3 kcal/mol therefore, for the chlorination reaction ! H o ! G o ~ ~ General Observations When the molecularity of reactants and products is the same, in reactions involving molecules of comparable size, the standard entropy change, ! S o , is close to zero. Because of the convenience in evaluating reaction mechanisms using the standard enthalpy change, ! H o , rather than the standard free energy change, ! G o , entropy changes will generally be ignored....
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