Ngā Tauira Pātai e Matapaki ana i ngā Pūtau Pūngao
Pendahuluan
Ko te pūtau hiko, e mōhiotia ana ko te pūtau hiko, he taputapu e huri ana i te pūngao matū hei pūngao hiko mā te tauhohenga redox (whakaiti-hauora). E rua ngā irahiko o te pūtau hiko, he mea hanga ki ngā konganuku rerekē, e rumakina ana ki roto i te irahiko, ā, e honoa ana e te piriti tote. I roto i tēnei tuhinga, ka matapakihia e mātou ētahi tauira e pā ana ki ngā pūtau hiko hei whakahōhonu ake i tō mātou māramatanga ki ā rātou mātāpono mahi me te tatau i te pūmanawa pūtau.
Te Ariā Taketake o ngā Pūtau Pūngao
I mua i te neke atu ki ngā tauira rapanga, he mea nui kia mārama ki ngā ariā me ngā wāhanga taketake e hanga ana i tētahi pūtau Voltaic:
1. Anode me te Cathode: I roto i te pūtau Voltaic, ko te anode te irahiko e puta ai te waikura, ā, ko te cathode te irahiko e puta ai te whakaiti. He utu kino tō te anode, ko te cathode ia he utu pai.
2. Ara Irahiko: Ka rere ngā irahiko mai i te anode ki te cathode mā roto i tētahi ara iahiko o waho, ka puta he iahiko hiko.
3. Pūmanawa Pūtau (E°pūtau): Ko te pūmanawa pūtau te rerekētanga pūmanawa i waenga i ngā irahiko e rua. Ka taea te tatau i te pūmanawa pūtau paerewa (E°pūtau) mā te whakamahi i te tātai:
\[
E° pūtau = E°cathode – E°anode
\]
ko \(E°cathode\) me \(E°anode\) ngā pūmanawa whakaiti paerewa o te cathode me te anode.
4. Piriti Tote: Ka whakatauritehia e tēnei piriti ngā utu katote i roto i ngā otinga irahiko e rua mā te tuku i te nekehanga o ngā katote.
Ngā Pātai Tauira me te Kōrero
Hei whakamārama i ēnei ariā, me matapaki tātou i ētahi tauira raruraru.
Tauira Pātai 1
Pātai:
Tātaihia te pūmanawa pūtau paerewa o tētahi pūtau Volta kei roto ko ngā irahiko Zn | Zn²⁺ (aq) me ngā irahiko Cu | Cu²⁺ (aq). E mōhiotia ana ko te pūmanawa whakaiti paerewa \(E°\) mō Zn²⁺ | Zn he -0.76 V, ā, ko \(E°\) mō Cu²⁺ | Cu he +0.34 V.
Kōrero:
Ko te taahiraa tuatahi ko te whakatau ko tēhea te anode me te cathode.
He nui ake te pūmanawa whakaiti kino o te Zn (-0.76 V) i te Cu (+0.34 V), nō reira ka mahi te Zn hei anode (pae waikura) me te Cu hei cathode (pae whakaiti).
Muri iho, ka whakamahia e mātou te tātai:
\[
E° pūtau = E°cathode – E°anode
\]
Whakakapia ngā uara e mōhiotia ana:
\[
E°pūtau = 0.34 V – (-0.76 V)
\]
\[
E°pūtau = 0.34 V + 0.76 V
\]
\[
E°pūtau = 1.10 V
\]
Nō reira, ko te pūmanawa paerewa o te pūtau he 1.10 V.
Tauira Pātai 2
Pātai:
He mea hanga te pūtau pūngao hiko mai i ngā irahiko Fe | Fe²⁺ me ngā irahiko Ag | Ag⁺. Ko te pūmanawa whakaiti paerewa mō te Fe²⁺ | Fe he -0.44 V, ā, mō te Ag⁺ | Ag he +0.80 V. Tātaihia te pūmanawa pūtau paerewa, ka tuhi i te tauhohenga pūtau.
Kōrero:
Pērā i mua, me whakatau tātou i te anode me te cathode. Nā te mea he kino ake te pūmanawa whakaiti o Fe²⁺/Fe i tō Ag⁺/Ag, ka mahi a Fe hei anode, ā, ko Ag hei cathode.
Whakamahia te tātai:
\[
E° pūtau = E°cathode – E°anode
\]
\[
E°pūtau = 0.80 V – (-0.44 V)
\]
\[
E°pūtau = 0.80 V + 0.44 V
\]
\[
E°pūtau = 1.24 V
\]
Ko te pūmanawa paerewa o te pūtau he 1.24 V.
Mō te tauhohenga pūtau whānui, ka whakakotahihia e mātou ngā tauhohenga waikura me te whakaiti:
– Tauhohenga i te anode: \( \text{Fe} \rightarrow \text{Fe}^{2+} + 2\text{e}^- \)
– Tauhohenga i te katote: \( \text{Ag}^+ + \text{e}^- \rightarrow \text{Ag} \)
Te whakataurite i te maha o ngā irahiko i ngā tauhohenga e rua:
\[
\text{Fe} \rightarrow \text{Fe}^{2+} + 2\text{e}^-
\]
\[
2\kākau{Ag}^+ + 2\kākau{e}^- \rightarrow 2\kākau{Ag}
\]
Tauhohenga whānui o te pūtau:
\[
\text{Fe} + 2\text{Ag}^+ \rightarrow \text{Fe}^{2+} + 2\text{Ag}
\]
Tauira Pātai 3
Pātai:
Tātaihia te pūmanawa pūtau i te 25°C mō tētahi pūtau Voltaic kei roto ko ngā irahiko Al | Al³⁺ me ngā irahiko Ni | Ni²⁺, mēnā ko te kukū o Al³⁺ he 0.001 M, ā, ko te kukū o Ni²⁺ he 1 M. E mōhiotia ana ko te \(E°\) mō Al³⁺ | Al he -1.66 V, ā, ko te \(E°\) mō Ni²⁺ | Ni he -0.23 V.
Kōrero:
Tuatahi, tautuhia te anode me te cathode:
– He kino ake te pūmanawa whakaiti o Al³⁺/Al (-1.66 V) i te Ni²⁺/Ni (-0.23 V), nō reira ko Al te anode, ā, ko Ni te cathode.
Ka tatauhia te pūmanawa pūtau paerewa penei:
\[
E° pūtau = E°cathode – E°anode
\]
\[
E°pūtau = -0.23 V – (-1.66 V)
\]
\[
E°pūtau = -0.23 V + 1.66 V
\]
\[
E°pūtau = 1.43 V
\]
Muri iho, ka whakamahia e mātou te Whārite Nernst hei tatau i te pūmanawa pūtau i raro i ngā āhuatanga kore-paerewa:
\[
E_{pūtau} = E°pūtau – \left( \frac{RT}{nF} \right) \ln Q
\]
Ko \( Q = \frac{[\text{Al}³⁺]}{[\text{Ni}²⁺]} \), ko R te pūmau hau (8.314 J/mol·K), ko T te pāmahana i Kelvin (298 K i te 25°C), ko F te pūmau Faraday (96485 C/mol), ā, ko n te maha o ngā irahiko (6 mō ngā tauhohenga e whai wāhi ana a Al³⁺ me Ni²⁺).
Whakakapia ngā uara e mōhiotia ana ki roto i te whārite:
\[
Q = \frac{0.001}{1} = 0.001
\]
\[
E_{pūtau} = 1.43 V – \left( \frac{8.314 \times 298}{6 \times 96485} \right) \ln 0.001
\]
\[
E_{pūtau} = 1.43 V – \left( \frac{2477.172}{578910} \right) \ln 0.001
\]
\[
E_{pūtau} = 1.43 V – (0.00428) \ln 0.001
\]
\[
\ln 0.001 = -6.907
\]
\[
E_{pūtau} = 1.43 V – (0.00428 \times -6.907)
\]
\[
E_{pūtau} = 1.43 V + 0.0295
\]
\[
E_{pūtau} = 1.4595 V
\]
Nō reira, ko te pūmanawa pūtau i tēnei āhuatanga he tata ki te 1.46 V.
Whakamutunga
He ariā taketake te pūtau hikohiko e huri ana i te pūngao matū hei pūngao hiko. Kua whakaurua e tēnei tuhinga ngā kaupapa matua o te ariā pūtau hikohiko, ā, kua whakaratohia hoki ngā tauira hei āwhina i te whakamārama i te tukanga tatau i te pūmanawa pūtau. Mā tēnei māramatanga, ko te tumanako ka pai ake te mārama o ngā kaipānui ki ngā pūtau hikohiko me ā rātou tono i roto i ngā horopaki rerekē.
