作者pengpengya (碰碰鴨)
看板Physics
標題[題目] 熱力學問題(綠皮)
時間Tue Dec 23 21:01:11 2014
[領域] 冶金熱力
[來源] Gaskell 習題9-1
[題目] 1 mole of solid Cr2O3 dissolved in a large volume of a liquid
Raoultian solution of Al2O3+Cr2O3 , in which X(Cr2O3) = 0.3 and T=2500K.
Melting point of Cr2O3: Tm(Cr2O3) = 2538K.
It can be assumed that △Sm(Al2O3)=△Sm(Cr2O3)
Please calculate entropy change by the addition
[瓶頸]
△S = △Sm + △Smix
有問題的是△Smix看不懂怎麼算
我是‧用公式代進去的
△Smix =-R(Xa‧ln(Xa) + Xb‧ln(Xb) )
Xa = 0.2,Xb = 0.5
帶進去發現答案不對
解答上的寫法是
It is stated that the solution is very large,
thus the entropy change is just the entropy of the added component which,
for 1 mole added,
is just the partial molar entropy of that component
thus
△Smix =-R ln(Xa)
我猜應該是觀念上隊公式的理解有點問題
但是不知道是哪邊有問題
我自己的解釋是公式可以理解成這樣
△Smix =-R(Xa1‧ln(Xa2) + Xb1‧ln(Xb2) )
Xa1,Xb1是溶質的莫爾分率
Xa2,Xb2是溶劑的莫爾分率
不知道這樣說不說得通
因為溶質是純的Cr2O3 → Xa1=1 , Xb1=0
而因為 N溶劑>>>>N溶質
因此混合前後Xa2不會改變
不知道這樣解釋能不能通
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※ 編輯: pengpengya (175.182.139.176), 12/23/2014 21:09:21