作者pengpengya (碰碰鸭)
看板Physics
标题[题目] 热力学问题(绿皮)
时间Tue Dec 23 21:01:11 2014
[领域] 冶金热力
[来源] Gaskell 习题9-1
[题目] 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
[瓶颈]
△S = △Sm + △Smix
有问题的是△Smix看不懂怎麽算
我是‧用公式代进去的
△Smix =-R(Xa‧ln(Xa) + Xb‧ln(Xb) )
Xa = 0.2,Xb = 0.5
带进去发现答案不对
解答上的写法是
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)
我猜应该是观念上队公式的理解有点问题
但是不知道是哪边有问题
我自己的解释是公式可以理解成这样
△Smix =-R(Xa1‧ln(Xa2) + Xb1‧ln(Xb2) )
Xa1,Xb1是溶质的莫尔分率
Xa2,Xb2是溶剂的莫尔分率
不知道这样说不说得通
因为溶质是纯的Cr2O3 → Xa1=1 , Xb1=0
而因为 N溶剂>>>>N溶质
因此混合前後Xa2不会改变
不知道这样解释能不能通
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※ 编辑: pengpengya (175.182.139.176), 12/23/2014 21:09:21