鉛酸松(song)下蓄電池正負極之間的關系

??松下蓄電池中的正負極它們直接是對立得到,但有同時參加化學反應。放電時松下蓄電池與外電路的負荷接通,電子從負極板經過外電路的負荷流往正極板,使正極板的電位下降。

??充電時,它是放電反應的逆過程。充電時松下蓄電池的正負兩極接通直流電源,當電源電壓高于蓄電池的電動勢E時,電流由蓄電池的正極流入,從蓄電池的負極流出,也就是電子由正極板經外電路流往負極板。

??電(dian)(dian)(dian)(dian)池的負(fu)極(ji)(ji)放電(dian)(dian)(dian)(dian)前,電(dian)(dian)(dian)(dian)極(ji)(ji)表(biao)面帶(dai)有(you)(you)負(fu)電(dian)(dian)(dian)(dian)荷(he),其附(fu)近溶(rong)液帶(dai)有(you)(you)正電(dian)(dian)(dian)(dian)荷(he),兩者處于平衡狀(zhuang)態。放電(dian)(dian)(dian)(dian)時(shi),立即有(you)(you)電(dian)(dian)(dian)(dian)子釋放給外電(dian)(dian)(dian)(dian)路。電(dian)(dian)(dian)(dian)極(ji)(ji)表(biao)面負(fu)電(dian)(dian)(dian)(dian)荷(he)減少,而金屬溶(rong)解的氧化反(fan)應進行緩慢Me－e→Me＋,不(bu)能及時(shi)補(bu)充電(dian)(dian)(dian)(dian)極(ji)(ji)表(biao)面電(dian)(dian)(dian)(dian)子的減少,電(dian)(dian)(dian)(dian)極(ji)(ji)表(biao)面帶(dai)電(dian)(dian)(dian)(dian)狀(zhuang)態發(fa)生變化。

??這種(zhong)表(biao)面負電荷(he)減少(shao)的狀態促(cu)進金屬中電子離開電極(ji),金屬離子Me＋轉(zhuan)入(ru)溶液,加速Me－e→Me＋反應進行。總有一(yi)個時刻,達到新的動態平(ping)衡。

??但與(yu)放(fang)電(dian)(dian)(dian)前相比,電(dian)(dian)(dian)極(ji)表面所(suo)帶(dai)負電(dian)(dian)(dian)荷數目減少了,與(yu)此對應的(de)電(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)勢(shi)變正。也就是電(dian)(dian)(dian)化學極(ji)化電(dian)(dian)(dian)壓變高,從而嚴重阻礙了正常的(de)充電(dian)(dian)(dian)電(dian)(dian)(dian)流。同(tong)理,電(dian)(dian)(dian)池正極(ji)放(fang)電(dian)(dian)(dian)時,電(dian)(dian)(dian)極(ji)表面所(suo)帶(dai)正電(dian)(dian)(dian)荷數目減少,電(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)勢(shi)變負。

??蓄電(dian)池中(zhong)正負極的電(dian)壓時如何產生的

??電(dian)(dian)(dian)(dian)(dian)(dian)流之所(suo)以能夠(gou)在導線中(zhong)(zhong)流動,也是(shi)因為在電(dian)(dian)(dian)(dian)(dian)(dian)流中(zhong)(zhong)有著高電(dian)(dian)(dian)(dian)(dian)(dian)勢能和(he)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)勢能之間(jian)(jian)的(de)差別。這種差別叫電(dian)(dian)(dian)(dian)(dian)(dian)勢差,也叫電(dian)(dian)(dian)(dian)(dian)(dian)壓。換句話說，在電(dian)(dian)(dian)(dian)(dian)(dian)路中(zhong)(zhong),任意兩點之間(jian)(jian)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)位差稱為這兩點的(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓。通常(chang)用(yong)字(zi)母U代表(biao)電(dian)(dian)(dian)(dian)(dian)(dian)壓,電(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)單位是(shi)伏特（V）,簡稱伏,用(yong)符(fu)號V表(biao)示(shi)。高電(dian)(dian)(dian)(dian)(dian)(dian)壓可(ke)以用(yong)千伏（kV）表(biao)示(shi),低(di)電(dian)(dian)(dian)(dian)(dian)(dian)壓可(ke)以用(yong)毫伏（mV）表(biao)示(shi),也可(ke)以用(yong)微伏(μv)表(biao)示(shi)。電(dian)(dian)(dian)(dian)(dian)(dian)壓是(shi)產生電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)原因。

??蓄電(dian)池(chi)(chi)的(de)電(dian)壓又稱電(dian)動勢(shi),蓄電(dian)池(chi)(chi)內有正、負兩個電(dian)極(ji),電(dian)動勢(shi)是兩個電(dian)極(ji)的(de)平(ping)衡電(dian)極(ji)電(dian)位之差,以鉛(qian)酸(suan)蓄電(dian)池(chi)(chi)為例,E=Ф+0-Ф-0+RT/F*In(αH2SO4/αH2O)。

??其中：E—電(dian)動勢

??Ф+0—正極標準(zhun)電(dian)極電(dian)位,其值為1.690

??Ф-0—負極標準(zhun)電極電位,其值為-0.356

??R—通用氣體常數(shu),其值為8.314

??T—溫度,與電池所處溫度有關(guan)

??F—法拉第常數,其(qi)值(zhi)為96500

??αH2SO4—硫酸(suan)的活度,與(yu)硫酸(suan)濃度有關

??αH2O—水(shui)的活度,與硫(liu)酸濃度有關

??從上式中可看(kan)出,鉛酸蓄電(dian)(dian)池的標準電(dian)(dian)動(dong)勢為(wei)1.690-（-0.0.356）=2.046V,因此(ci)蓄電(dian)(dian)池的標稱電(dian)(dian)壓(ya)為(wei)2V。鉛酸蓄電(dian)(dian)池的電(dian)(dian)動(dong)勢還與溫度(du)及硫酸濃度(du)有關。

??松下蓄電池放電時,正極反應為:PbO2+4H++SO42-+2e-=PbSO4+2H2O

??負極反(fan)應(ying):Pb+SO42--2e-=PbSO4

??總反(fan)應(ying)(ying):PbO2+Pb+2H2SO4===2PbSO4+2H2O(向右反(fan)應(ying)(ying)是放電(dian),向左(zuo)反(fan)應(ying)(ying)是充(chong)電(dian))

??充(chong)電時,如果(guo)接(jie)反,"燒"的原理是(shi),上面這個化學方程式中(zhong),"充(chong)電"反應不(bu)能(neng)按理論(lun)進(jin)行,倒置電池中(zhong)的的材料(liao)不(bu)能(neng)循(xun)環(huan)利(li)用,就"燒"壞了.