Nā nīnau hoʻohālike a me ke kūkākūkā ʻana o ka hiki ke hoʻohana ʻia ke Electrode maʻamau
Pendahuluan
He manaʻo koʻikoʻi ka hiki ke hoʻoheheʻe ʻia ke electrode maʻamau i ka electrochemistry e wehewehe ana i ka hiki o kahi electrode ke huki i nā electrons. Hoʻohana ʻia kēia manaʻo i nā helu kelepona electrochemical a me ka hoʻoholo ʻana i ke ʻano o nā hopena redox. Ana ʻia ka hiki ke hoʻoheheʻe ʻia ke electrode maʻamau (E°) ma lalo o nā kūlana maʻamau, ʻo ia hoʻi ma kahi ʻano o 1 M, kahi kaomi o 1 atm, a me ka mahana o 25°C (298 K). Ma kēia ʻatikala, e kūkākūkā mākou i kekahi mau laʻana o nā pilikia hiki ke hoʻoheheʻe ʻia ke electrode maʻamau a kūkākūkā hohonu iā lākou.
Manaʻo Kumu o ka Mana Uila Maʻamau
ʻO ka hiki ke hoʻemi ʻia ke electrode maʻamau, i hōʻike ʻia ʻo E°, e wehewehe ana i ke ʻano o kahi ʻano kemika e hoʻemi ʻia (e ʻae i nā electrons). ʻO ka ʻoi aku ka maikaʻi o ka waiwai E°, ʻoi aku ka nui o ke ʻano o ka hoʻemi ʻia ʻana o nā ʻano. I ka ʻaoʻao ʻē aʻe, ʻo ka ʻoi aku ka maikaʻi ʻole o ka waiwai E°, ʻoi aku ka nui o ke ʻano o ka oxidized ʻia (nalowale nā electrons).
Hāʻawi ka papa kuhikuhi electrode potential maʻamau i nā waiwai E° no nā ʻano hana redox like ʻole, a hoʻohana ʻia kēia mau waiwai e helu i nā potentials cell electrochemical.
Laʻana Nīnau 1
Nīnau:
Hāʻawi ʻia i nā hopena hapalua ʻelua a me ko lākou mau hiki ke electrode:
– Ag⁺(aq) + e⁻ → Ag(s), E° = +0.80 V
– Cu²⁺(aq) + 2e⁻ → Cu(s), E° = +0.34 V
E hoʻoholo i ka hiki ke kelepona (E°_cell) no ke kelepona galvanic i hoʻokumu ʻia e kēia mau hopena hapalua ʻelua.
Kūkākūkā:
No ka hoʻoholo ʻana i ka hiki ke kelepona, pono mākou e ʻike i ka anode a me ka cathode. I loko o kahi kelepona galvanic, ʻo ka mea me ka hiki ke electrode maʻamau maikaʻi aʻe e hana ma ke ʻano he cathode (kahi o ka hōʻemi ʻana) a ʻo ka mea me ka mea maikaʻi ʻole aʻe e hana ma ke ʻano he anode (kahi o ka oxidation).
1. E ʻike i ka Anode a me ka Cathode:
– Ag⁺ + e⁻ → Ag, E° = +0.80 V (ʻoi aku ka maikaʻi, no laila cathode)
– Cu²⁺ + 2e⁻ → Cu, E° = +0.34 V (ʻoi aku ka maikaʻi ʻole, no laila anode)
2. E hoʻoholo i nā hopena oxidation a me ka hōʻemi:
– Cathode (hoʻemi): Ag⁺ + e⁻ → Ag, E°_cathode = +0.80 V
– Anode (oxidation): Cu → Cu²⁺ + 2e⁻, E°_anode = -0.34 V (e hoʻohuli i ke kuhikuhi o ka hopena a me ka hōʻailona hiki)
3. Ke helu ʻana i ka E°_cell:
\[
E°_{cell} = E°_{cathode} – E°_{anode}
\]
\[
E°_{sel} = 0.80\, \text{V} – (-0.34\, \text{V})
\]
\[
E°_{sel} = 0.80\, \text{V} + 0.34\, \text{V} = 1.14\, \text{V}
\]
No laila, ʻo ka hiki ke kelepona (E°_cell) he +1.14 V.
Laʻana Nīnau 2
Nīnau:
Hāʻawi ʻia ka hopena ma lalo me kona hiki ke electrode:
– Fe³⁺(aq) + e⁻ → Fe²⁺(aq), E° = +0.77 V
– Zn²⁺(aq) + 2e⁻ → Zn(s), E° = -0.76 V
E hoʻoholo i ka hiki ke hana ʻia o ke kelepona (E°_cell) no kahi kelepona galvanic me ka hoʻohana ʻana i nā hapalua-reactions ʻelua, a kākau i ka hopena kelepona piha.
Kūkākūkā:
E like me ka mea ma mua, pono e ʻike mua i ka anode a me ka cathode.
1. E ʻike i ka Anode a me ka Cathode:
– Fe³⁺ + e⁻ → Fe²⁺, E° = +0.77 V (ʻoi aku ka maikaʻi, no laila cathode)
– Zn²⁺ + 2e⁻ → Zn, E° = -0.76 V (ʻoi aku ka maikaʻi ʻole, no laila anode)
2. E hoʻoholo i nā hopena oxidation a me ka hōʻemi:
– Cathode (hoʻemi): Fe³⁺ + e⁻ → Fe²⁺, E°_cathode = +0.77 V
– Anode (oxidation): Zn → Zn²⁺ + 2e⁻, E°_anode = -0.76 V (e hoʻohuli i ke kuhikuhi o ka hopena a me ka hōʻailona hiki)
3. Ke kaulike ʻana i nā electrons:
Pono ka hopena holoʻokoʻa e kaulike i ka helu o nā electrons:
\[
2(\kikokikona{Fe}^{3+} + e⁻ → \kikokikona{Fe}^{2+})
\]
\[
\kikokikona{Zn} → \kikokikona{Zn}^{2+} + 2e⁻
\]
No laila, ʻo ka pane piha o ke kelepona:
\[
2\text{Fe}^{3+} + \text{Zn} → 2\text{Fe}^{2+} + \text{Zn}^{2+}
\]
4. Ke helu ʻana i ka E°_cell:
\[
E°_{cell} = E°_{cathode} – E°_{anode}
\]
\[
E°_{sel} = 0.77\, \text{V} – (-0.76\, \text{V})
\]
\[
E°_{sel} = 0.77\, \text{V} + 0.76\, \text{V} = 1.53\, \text{V}
\]
No laila, ʻo ka hiki ke kelepona (E°_cell) he +1.53 V.
Laʻana Nīnau 3
Nīnau:
E hāʻawi i ka hiki o ke kelepona a hoʻopau i ka hopena o ke kelepona no kahi kelepona galvanic me ka hoʻohana ʻana i kēia hopena:
– MnO₂(s) + 4H⁺(aq) + 2e⁻ → Mn²⁺(aq) + 2H₂O(l), E° = +1.23 V
– Cr³⁺(aq) + e⁻ → Cr²⁺(aq), E° = -0.50 V
Kūkākūkā:
1. E ʻike i ka Anode a me ka Cathode:
– MnO₂ + 4H⁺ + 2e⁻ → Mn²⁺ + 2H₂O, E° = +1.23 V (ʻoi aku ka maikaʻi, no laila cathode)
– Cr³⁺ + e⁻ → Cr²⁺, E° = -0.50 V (ʻoi aku ka maikaʻi ʻole, no laila anode)
2. E hoʻoholo i nā hopena oxidation a me ka hōʻemi:
– Cathode (hōʻemi): MnO₂ + 4H⁺ + 2e⁻ → Mn²⁺ + 2H₂O, E°_cathode = +1.23 V
– Anode (oxidation): Cr²⁺ → Cr³⁺ + e⁻, E°_anode = +0.50 V (e hoʻohuli i ke kuhikuhi o ka hopena a me ka hōʻailona hiki)
3. Ke kaulike ʻana i nā electrons:
Pono ka hopena holoʻokoʻa e kaulike i ka helu o nā electrons:
\[
2(\kikokikona{Cr}^{3+} + e⁻ → \kikokikona{Cr}^{2+})
\]
\[
\kikokikona{MnO}_2 + 4\kikokikona{H}^+ + 2e⁻ → \kikokikona{Mn}^{2+} + 2\kikokikona{H}_2\kikokikona{O}
\]
No laila, ʻo ka pane piha o ke kelepona:
\[
\kikokikona{MnO}_2 + 4\kikokikona{H}^+ + 2\kikokikona{Cr}^{3+} → \kikokikona{Mn}^{2+} + 2\kikokikona{Cr}^{2+} + 2\kikokikona{H}_2\kikokikona{O}
\]
4. Ke helu ʻana i ka E°_cell:
\[
E°_{cell} = E°_{cathode} – E°_{anode}
\]
\[
E°_{sel} = 1.23\, \text{V} – (-0.50\, \text{V})
\]
\[
E°_{sel} = 1.23\, \text{V} + 0.50\, \text{V} = 1.73\, \text{V}
\]
No laila, ʻo ka hiki ke kelepona (E°_cell) he +1.73 V.
Ka hopena
He mea koʻikoʻi ka hoʻomaopopo ʻana i nā potentials electrode maʻamau i ka electrochemistry no ka hoʻoholo ʻana i nā ʻano hana redox a me nā potentials cell electrochemical. Ma ka hoʻohana ʻana i nā ʻanuʻu i kūkākūkā ʻia ma luna, hiki iā mākou ke helu maʻalahi i ka potential cell o kahi hana redox i hāʻawi ʻia. Hoʻohana ʻia nā potentials electrode maʻamau e hoʻoholo i ka anode a me ka cathode i loko o kahi cell galvanic, a me ka helu ʻana i ka potential cell holoʻokoʻa, e hōʻike ana i ka pono a me ke kuhikuhi o ka hana redox.
