化學兩題 求答案

同學抱歉, 但兩題皆錯, 改正後仍錯.

要非常留心: 小楷的k 是反應速率常數, 用Arrhenius equation 計算.
根據方程, 溫度越高, 反應速率越高; 除非你的反應的活化能是零 (例如核裂變).
這類的反應速率, 通常是指"反應物生成產物" 的方向, 相反方向的叫k-1 , "-1"下標.
其實想想也是合理: 溫度升高, 分子平均動能上升, 分子運動速度增加, 使分子間有效碰撞的頻率提高.
無論反應是放熱吸熱, 正方向的反應速率均會提高; 當然反方向反應也會加速.

至於平衡常數, 那是大楷的K, 用Van't Hoff equation 計算.
正方向為放熱反應時, 加熱使K值下降, 平衡點移向左方(反應物); 冷卻使K值上升, 平衡點移向右方(產物).


1. C
熱焓轉變, 在Arrhenius equation 沒有提及.

2. A
放熱反應, K下降; 加熱, k 上升.


answers for both questions are wrong, even after making correction.

note that "k" is reaction rate constant, determined by Arrhenius equation.
according to equation, rate constant increases when temp. increases, unless the activation energy of the reaction is zero (e.g. nuclear fission).
when we're talking about "rate constant", it means forward reaction; for backward reaction, it's k-1 ("-1" in subscript).

when temp. increases, both average kinetic energy and moving speed of molecules increase, so is the frequency of effective collision.
no matter the reaction is exothermic or endothermic, rate constants for both forward and backward reaction increases.


"K" is the equilibrium constant, calculated by Van't Hoff equation.
exothermic rxn:
temp. increase leads to reduction of K; eqm. position shifts to left.
temp. decrease leads to increase in K; eqm. pos. shifts to right.


1. C
enthalpy change of reaction is not considered in Arrhenius eq.

2. A
exothermic rxn: temp. increase, K decreases; k increases anyway.

第一題；
因溫度升高，反應速率常數增加，此為「吸熱反應」。
選「ｂ」

第二題：
一放熱反應，反應式可如此假設－－Ａ＋Ｂ→Ｃ＋△H
當溫度提高，反應向右走，則原ｋ值減少。
故選「ｃ」




這是在下以自身化工所學所提出之解，若有錯誤，還請多多見諒。

2011-04-20 10:00:30 補充：
啊！不好意思，第二題當溫度提高，該是向左走才對，所以該選ｄ。
而ｋ值減少是沒錯的。

抱歉抱歉，在下一時手殘打錯字。