化学SUB题目讨论

远地点UID: 2651690

practice book 上的一道题，ETS寄来的那本

33    Two cylinders, one containing 1 mole of C4H10 gas at 1 atm and the other containing 1 mole of CH4 gas at 1 atm, are at 288K. If each gas absords 100J of heat under conditions of constant volume, which of the following is true?

A  the temoerature of the CH4 increases more than the temperature of the C4H10
B  the internal energy of both the CH4 and the C4H10 decrease
C  the heat capacyty of the C4H10 is less than the heat capacity of the CH4
D  the entropy of both the CH4 and C4H10 decrease
E   the heat transferred to the C4H10 is greater than the heat transferred to CH4.


答案是A， 但是我总觉得条件不全，不能算出A。 我想到的公式的 Q=m*C*温度差
请高手们解答。

sunwei0UID: 2227404

可是其他几个都可以排除啊。。。

远地点UID: 2651690

但是A C不能判断啊

sunwei0UID: 2227404

CH4的heat capacity比较小这个问题是不是当作常识了，所以就没单独列出来啊

远地点UID: 2651690

4# sunwei0
啊。。。。。。是这样啊
是不是说，随着烷烃的碳原子数，增加，heat capacity就增加啊？

sunwei0UID: 2227404

据我所知，碳原子越多heat capacity越高，不饱和键越多heat capacity越高

Quince8UID: 2716184

因为C4H10的化学键比CH4多，所以分子振动与转动多，所以Cv，m就大。

SakurawindUID: 2378663

刚在TS帖完……

as to option B, internal energy (U) is only a function of temperture (T). Obviously when a system absorbs heat, T will raise.
as to option D, we have: dU=TdS-PdV=TdS, U=Q+W=Q
therefore, dU=TdS
since T increases, the entropy (S) for both gases also increases.
option E is clearly a wrong answer

So by using the process of elimination we got two left: A and C, and they're contradictory to each other.
I wiki the term "temperature" and took a piece of excerpt:
"A diatomic gas, with extra degrees of freedom rotation and vibration, will require a higher energy input to change the temperature by a certain amount, i.e. it will have a higher heat capacity than a monatomic gas."
Probably we can put this into the explanation of the above question, because butane (C4H10) does have larger molecular size and deserves to consume more heat to raise equivalent T as methane (CH4)