Nā nīnau hoʻohālike e kūkākūkā ana i nā pūnaewele Voltaic
Pendahuluan
ʻO kahi cell voltaic, i ʻike ʻia hoʻi he cell galvanic, he mea hana ia e hoʻololi i ka ikehu kemika i ikehu uila ma o kahi hopena redox (oxidation-reduction). Loaʻa i kahi cell voltaic ʻelua mau electrodes, i hana pinepine ʻia me nā metala like ʻole, i hoʻokomo ʻia i loko o kahi electrolyte a hoʻopili ʻia e kahi alahaka paʻakai. Ma kēia ʻatikala, e kūkākūkā mākou i kekahi mau laʻana e pili ana i nā cell voltaic e hoʻoikaika i ko mākou ʻike i kā lākou mau loina hana a pehea e helu ai i ka hiki o ke cell.
Kumumanaʻo Kumu o nā Kelepona Voltaic
Ma mua o ka neʻe ʻana i nā pilikia hoʻohālike, he mea nui e hoʻomaopopo i nā manaʻo kumu a me nā ʻāpana e hana ana i kahi cell Voltaic:
1. ʻAnode a me Cathode: I loko o kahi cell Voltaic, ʻo ka anode ka electrode kahi e hana ʻia ai ka oxidation, a ʻo ka cathode ka electrode kahi e hana ʻia ai ka hōʻemi. He uku maikaʻi ʻole ko ka anode, ʻoiai he uku maikaʻi ko ka cathode.
2. Ala Uila: Ke kahe nei nā uila mai ka anode a i ka cathode ma o kahi kaapuni waho, e hana ana i kahi au uila.
3. Ka Mana o ke Kelepona (E°cell): ʻO ka mana o ke kelepona ka ʻokoʻa o ka mana ma waena o nā electrodes ʻelua. Hiki ke helu ʻia ka mana o ke kelepona maʻamau (E°cell) me ka hoʻohana ʻana i ke ʻano hana:
\[
E°cell = E°cathode – E° anode
\]
kahi ʻo \(E°cathode\) a me \(E°anode\) nā potentials hōʻemi maʻamau o ka cathode a me ka anode.
4. Alahaka Paʻakai: Hoʻoponopono kēia alahaka i nā uku ion i loko o nā hopena electrolyte ʻelua ma ka ʻae ʻana i ka neʻe ʻana o nā ion.
Nā Nīnau Laʻana a me ke Kūkākūkā
I mea e wehewehe ai i kēia mau manaʻo, e kūkākūkā kākou i kekahi mau pilikia hoʻohālike.
Laʻana Nīnau 1
Nīnau:
E helu i ka hiki ke hoʻemi maʻamau o kahi kelepona Volta i haku ʻia me nā electrodes Zn | Zn²⁺ (aq) a me nā electrodes Cu | Cu²⁺ (aq). Ua ʻike ʻia ʻo ka hiki ke hoʻemi maʻamau \(E°\) no Zn²⁺ | Zn he -0.76 V a ʻo \(E°\) no Cu²⁺ | Cu he +0.34 V.
Kūkākūkā:
ʻO ka hana mua, ʻo ia ke hoʻoholo i ka anode a me ka cathode.
ʻOi aku ka nui o ka hiki ke hoʻemi maikaʻi ʻole o Zn (-0.76 V) ma mua o Cu (+0.34 V), no laila e hana ʻo Zn ma ke ʻano he anode (kahua oxidation) a ʻo Cu ma ke ʻano he cathode (kahua hoʻemi).
A laila, hoʻohana mākou i ke ʻano hana:
\[
E°cell = E°cathode – E° anode
\]
E pani i nā waiwai i ʻike ʻia:
\[
E°kelepona = 0.34 V – (-0.76 V)
\]
\[
E°kelepona = 0.34 V + 0.76 V
\]
\[
E°kelepona = 1.10 V
\]
No laila, ʻo ka mana o ke kelepona maʻamau he 1.10 V.
Laʻana Nīnau 2
Nīnau:
Hana ʻia kahi cell Voltaic me nā electrodes Fe | Fe²⁺ a me nā electrodes Ag | Ag⁺. ʻO ka hiki ke hoʻemi maʻamau no Fe²⁺ | Fe he -0.44 V a no Ag⁺ | Ag he +0.80 V. E helu i ka hiki ke hoʻemi maʻamau a kākau i ka hopena o ke kelepona.
Kūkākūkā:
E like me ma mua, pono mākou e hoʻoholo i ka anode a me ka cathode. ʻOiai ʻoi aku ka maikaʻi ʻole o ka hiki ke hoʻemi ʻia o Fe²⁺/Fe ma mua o Ag⁺/Ag, e hana ʻo Fe ma ke ʻano he anode a ʻo Ag ma ke ʻano he cathode.
E hoʻohana i ke ʻano hana:
\[
E°cell = E°cathode – E° anode
\]
\[
E°kelepona = 0.80 V – (-0.44 V)
\]
\[
E°kelepona = 0.80 V + 0.44 V
\]
\[
E°kelepona = 1.24 V
\]
ʻO ka mana o ke kelepona maʻamau he 1.24 V.
No ka hopena holoʻokoʻa o ke kelepona, hoʻohui mākou i nā hopena oxidation a me ka hōʻemi:
– Ka pane ʻana ma ka anode: \( \text{Fe} \rightarrow \text{Fe}^{2+} + 2\text{e}^- \)
– Ka pane ʻana ma ke cathode: \( \text{Ag}^+ + \text{e}^- \rightarrow \text{Ag} \)
Ke kaulike nei i ka helu o nā electrons i nā hopena ʻelua:
\[
\text{Fe} \rightarrow \text{Fe}^{2+} + 2\text{e}^-
\]
\[
2\kikokikona{Ag}^+ + 2\kikokikona{e}^- \rightarrow 2\kikokikona{Ag}
\]
Ka hopena holoʻokoʻa o ke kelepona:
\[
\text{Fe} + 2\text{Ag}^+ \rightarrow \text{Fe}^{2+} + 2\text{Ag}
\]
Laʻana Nīnau 3
Nīnau:
E helu i ka hiki ke loaʻa i loko o ke kelepona ma 25°C no kahi kelepona Voltaic i haku ʻia me nā electrodes Al | Al³⁺ a me nā electrodes Ni | Ni²⁺, inā he 0.001 M ka nui o Al³⁺ a he 1 M ka nui o Ni²⁺. Ua ʻike ʻia ʻo \(E°\) no Al³⁺ | Al he -1.66 V a ʻo \(E°\) no Ni²⁺ | Ni he -0.23 V.
Kūkākūkā:
ʻO ka mea mua, e hoʻoholo i ka anode a me ka cathode.
– ʻOi aku ka maikaʻi ʻole o ka hiki ke hoʻemi o Al³⁺/Al (-1.66 V) ma mua o Ni²⁺/Ni (-0.23 V), no laila ʻo Al ka anode a ʻo Ni ka cathode.
Ua helu ʻia ka hiki ke loaʻa i ke kelepona maʻamau penei:
\[
E°cell = E°cathode – E° anode
\]
\[
E°kelepona = -0.23 V – (-1.66 V)
\]
\[
E°kelepona = -0.23 V + 1.66 V
\]
\[
E°kelepona = 1.43 V
\]
ʻO ka mea aʻe, hoʻohana mākou i ka Nernst Equation e helu i ka hiki ke loaʻa i ke kelepona ma lalo o nā kūlana maʻamau ʻole:
\[
E_{kelepona} = E°kelepona – \left( \frac{RT}{nF} \right) \ln Q
\]
Ma hea \( Q = \frac{[\text{Al}³⁺]}{[\text{Ni}²⁺]} \), ʻo R ke kūpaʻa kinoea (8.314 J/mol·K), ʻo T ka mahana ma Kelvin (298 K ma 25°C), ʻo F ke kūpaʻa Faraday (96485 C/mol), a ʻo n ka helu o nā electrons (6 no nā hopena e pili ana iā Al³⁺ a me Ni²⁺).
E hoʻololi i nā waiwai i ʻike ʻia i loko o ka hoohalike:
\[
Q = \frac{0.001}{1} = 0.001
\]
\[
E_{kelepona} = 1.43 V – \left( \frac{8.314 \times 298}{6 \times 96485} \right) \ln 0.001
\]
\[
E_{kelepona} = 1.43 V – \left( \frac{2477.172}{578910} \right) \ln 0.001
\]
\[
E_{kelepona} = 1.43 V – (0.00428) \ln 0.001
\]
\[
\ln 0.001 = -6.907
\]
\[
E_{kelepona} = 1.43 V – (0.00428 \times -6.907)
\]
\[
E_{kelepona} = 1.43 V + 0.0295
\]
\[
E_{kelepona} = 1.4595 V
\]
No laila, ʻo ka hiki o ke kelepona ma kēia kūlana ma kahi o 1.46 V.
Ka hopena
He manaʻo nui ka cell voltaic i ka electrochemistry e hoʻololi i ka ikehu kemika i ikehu uila. Ua hoʻolauna kēia ʻatikala i nā kumu o ke kumumanaʻo cell Voltaic a ua hāʻawi i nā laʻana e kōkua i ka wehewehe ʻana i ke kaʻina hana o ka helu ʻana i ka hiki o ke cell. Me kēia ʻike, e loaʻa i ka poʻe heluhelu kahi ʻike maikaʻi o nā cell Voltaic a me kā lākou noi ma nā ʻano like ʻole.
