I don\'t quite understand how we canget entropy with these number. I know, that

Question

I don't quite understand how we canget entropy with these number. I know, that

S(universe)=-DH/T but that is for theuniverse and wouldn't apply?

Or

At these points we're at equilibriumtherefor deltaG is 0?

The melting points, boiling points,heat of fusion, heat of vaporization of four substances listedbelow. Calculate DS fus and DS vap foreach of these substances. Explain why DSvap is greaterthan DSfus for all these compounds.

Compound       t mp(0C)    DHfus(kJ/mol)     tbp(0C)   DHvap (kJ/mol)

CH3Cl             -97.73       6.45                   -24.2       21.6

CH3SH           -123.         5.91                   +6.2        24.5  

Explanation / Answer

For CH3Cl : ------------- S fus = H fus / T mp T mp = temperature = -97.73oC = -97.73+ 273 = 175.27 K So S fus = 6.45* 1000 J / mol / 175.27 K = 36.8 J / mol - K S vap = H vap / T T bp = temperature = -24.2oC =-24.2+ 273 = 248.8 K So S fus = 21.6* 1000 J / mol / 248.8 K= 86.8 J /mol - K For CH3SH : ------------- S fus = H fus / T mp T mp = temperature = -123 oC = -123+ 273 = 150 K So S fus = 5.91* 1000 J / mol / 150K = 39.4 J / mol - K S vap = H vap / T T bp = temperature = 6.2 oC = 6.2+ 273 = 279.2K So S fus = 24.5 * 1000 J / mol / 279.2K= 87.8 J / mol - K Entropy means the randomness of molecules. In solid state state the molecules are closly packed==> the randomness decreases.Where as in vapour state themolecules are far away to each other ==> randomness more ==>entropy more T bp = temperature = -24.2oC =-24.2+ 273 = 248.8 K So S fus = 21.6* 1000 J / mol / 248.8 K= 86.8 J /mol - K For CH3SH : ------------- S fus = H fus / T mp T mp = temperature = -123 oC = -123+ 273 = 150 K So S fus = 5.91* 1000 J / mol / 150K = 39.4 J / mol - K S vap = H vap / T T bp = temperature = 6.2 oC = 6.2+ 273 = 279.2K So S fus = 24.5 * 1000 J / mol / 279.2K= 87.8 J / mol - K Entropy means the randomness of molecules. In solid state state the molecules are closly packed==> the randomness decreases.Where as in vapour state themolecules are far away to each other ==> randomness more ==>entropy more T mp = temperature = -123 oC = -123+ 273 = 150 K So S fus = 5.91* 1000 J / mol / 150K = 39.4 J / mol - K S vap = H vap / T T bp = temperature = 6.2 oC = 6.2+ 273 = 279.2K So S fus = 24.5 * 1000 J / mol / 279.2K= 87.8 J / mol - K Entropy means the randomness of molecules. In solid state state the molecules are closly packed==> the randomness decreases.Where as in vapour state themolecules are far away to each other ==> randomness more ==>entropy more T bp = temperature = 6.2 oC = 6.2+ 273 = 279.2K So S fus = 24.5 * 1000 J / mol / 279.2K= 87.8 J / mol - K Entropy means the randomness of molecules. In solid state state the molecules are closly packed==> the randomness decreases.Where as in vapour state themolecules are far away to each other ==> randomness more ==>entropy more

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