平衡电极电势和电池电动势【】

1、4 4 平衡电极电势和电池电动势平衡电极电势和电池电动势 电池电动势等于两个电极电势的差值。电池电动势等于两个电极电势的差值。 实验只能测得两个电极构成的电池的电动势实验只能测得两个电极构成的电池的电动势E，而无法测得单独电极的电极电势，而无法测得单独电极的电极电势 。 若选定一个电极作为标准，使其与任意其它若选定一个电极作为标准，使其与任意其它电极组成电池，测其电动势，就可得出各电电极组成电池，测其电动势，就可得出各电极的相对电极电势极的相对电极电势 。 利用两电极的相对电极电势，可以方便的求利用两电极的相对电极电势，可以方便的求得由它们组成的电池的电动势，得由它们组成的电池的电动势，E=

2、+ 。镀铂黑的铂片浸入镀铂黑的铂片浸入aH+=1的溶液中并以的溶液中并以pH2=1p 的纯氢气不断的纯氢气不断冲击到冲击到Pt电极上。电极上。规定：在任意温度下：规定：在任意温度下：o2 (/) 0 HHoPt（铂黑）（铂黑）H2(g, p=1p )H+(aq, a+=1)o标准氢电极标准氢电极以标准氢电极作氧化极，即负极；而将待定的电极作以标准氢电极作氧化极，即负极；而将待定的电极作还原极还原极，即正极，组成电池：，即正极，组成电池： (Pt) H2(pH2=1p0) | H+(a H+=1)| 待测待测然后用电位差计测量该电池的电动势，这个数值和符然后用电位差计测量该电池的电动势，这个数值

3、和符号就是待测电极的号就是待测电极的氢标还原电极电势氢标还原电极电势的数值和符号的数值和符号。例：H2(g,p0)H+(aq, a+=1)Cu2+(aq, aCu)Cu222 (/) If E 0, (/) 0 E 0, (/) 0 CuCuECuCuCuCuE (待测待测) 0 (H+/H2) = (待测待测)0= (待测待测)饱和甘汞电极示意图电极的电极的Nernst方程方程)1ln2()1ln2()1ln21ln2()(ln2)(/)()()(/)()(1222221222222212aZnoZnZnaCuoCuaZnaCuoZnZnoCuaCuaZnoaFRTaFRTaFRTaFRTa

4、aFRTEE由由Nernst方程：方程：)()(lnOXaREaZFRTo此即电极的此即电极的Nernst方程，注意活度商是方程，注意活度商是还原态还原态/氧化态氧化态.电池：电池：Zn(s)|Zn2+|Cu2+|Cu(s) 电化学反应：电化学反应：Zn(s)+Cu2+Zn2+Cu(s)对于任一单个电极电势：对于任一单个电极电势：5 可逆电极的种类可逆电极的种类 第一类电极第一类电极(这类电极一般只有一个相界面这类电极一般只有一个相界面) a. 金属与其阳离子组成的电极金属与其阳离子组成的电极b. 气体电极气体电极第二类电极第二类电极(存在两个相界面存在两个相界面)a. 金属金属-难溶盐及其阴

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