Tauira Pātai Kōrerorero Te Ine i te Pūmanawa Hikohiko
He wāhanga nui o te matū hiko te ine i te pūmanawa hiko. Ko te matū hiko he peka o te matū e ako ana i te whanaungatanga i waenga i ngā tauhohenga matū me te hiko. He mea nui te āheinga ki te ine i te pūmanawa hiko, inā koa i roto i ngā tono pēnei i ngā pākahiko, te waikura, me te hikohiko. I roto i tēnei tuhinga, ka matapakihia e mātou ētahi tauira raruraru me ā rātou otinga i roto i te horopaki o te ine i te pūmanawa hiko.
Te Mārama ki te Pūmanawa Hikohiko
Ko te pūmanawa hiko, te pūmanawa pūtau rānei, ko te rerekētanga pūmanawa hiko i waenga i ngā hiko e rua i roto i te pūtau hiko. Ka taea te ine mā te whakamahi i ngā tikanga maha, tae atu ki te whakamahi i te pūmanawa tohutoro paerewa pērā i te hiko kalomel kua kōtuitia (SCE) me te hiko hiriwa/hiriwa kōhaita (Ag/AgCl). Ko te pūmanawa paerewa hei paearu mō te ine me te whakatairite i ngā pūmanawa o ētahi atu hiko.
Tātai Taketake
Ka taea te whakaatu i te pūmanawa pūtau (\( E_{\text{sel}} \)) i raro i ngā tikanga paerewa mā te tātai:
\[ E_{\kuputuhi{pūtau}}^\circ = E_{\kuputuhi{katode}}^\circ – E_{\kuputuhi{anode}}^\circ \]
ranei
\[ E_{\text{pūtau}} = E_{\text{katode}} – E_{\text{anode}} \]
Ngā Pātai Tauira me te Kōrero
Tauira Pātai 1: Te Ine i te Pūmanawa o te Pūtau Galvanic
Pātai:
Ki te hoatu he pūtau karawaka kei roto ko te irahiko konutea (Zn) me te irahiko parahi (Cu), e rumakina ana ki roto i te wairewa o te ZnSO₄ me te CuSO₄. Ko te pūmanawa irahiko paerewa (E°) o te konutea he -0.76 V, ā, ko te parahi he +0.34 V. Tātaihia te pūmanawa pūtau, ka whakatau i te ahunga o te rere o te irahiko.
Whakautu:
Ko te taahiraa tuatahi ko te tautuhi i te anode me te cathode. I roto i te electrochemistry, ko te anode te wāhi e puta ai te waikura (te tuku i ngā irahiko), ā, ko te cathode te wāhi e puta ai te whakaiti (te tango i ngā irahiko).
– Ka pāngia ngā irahiko konutea (Zn) e te waikura:
\[
\kāhua{Zn} \rightarrow \kāhua{Zn}^{2+} + 2\kāhua{e}^- \quad (E^\circ = -0.76 \kāhua{ V})
\]
– Ka whakaitihia ngā hiko parahi (Cu):
\[
\text{Cu}^{2+} + 2\text{e}^- \rightarrow \text{Cu} \quad (E^\circ = +0.34 \text{ V})
\]
Mā te whakamahi i te tātai pūmanawa pūtau:
\[
E_{\kākau{pūtau}}^\circ = E_{\kākau{katode}}^\circ – E_{\kākau{anode}}^\circ
= 0.34 \text{ V} – (-0.76 \text{ V})
= 0.34 \text{ V} + 0.76 \text{ V}
= 1.10 \text{ V}
\]
Ko te ahunga o te rere o te irahiko mai i te irahiko konutea (anode) ki te irahiko parahi (cathode).
Tauira Pātai 2: Pūmanawa Pūtau Kore-Paerewa
Pātai:
Ka hangaia he pūtau hikohiko mā te whakamahi i tētahi irahiko hiriwa (Ag) i roto i tētahi otinga 0.1 M AgNO₃ me tētahi irahiko konutea (Zn) i roto i tētahi otinga 0.01 M ZnSO₄. Ko te pūmanawa paerewa o te hiriwa he +0.80 V, ā, ko te konutea he -0.76 V. Tātaihia te pūmanawa pūtau i raro i ngā āhuatanga kore-paerewa mā te whakamahi i te Whārite Nernst.
Whakautu:
Ko te whārite Nernst e homai ana e:
\[
E = E^\circ – \frac{RT}{nF} \ln Q
\]
Kei hea:
– Ko te pūmanawa pūtau paerewa te \( E^\circ \),
– Ko te pūmau hau whānui (8.314 J/mol K) te \( R \),
– Ko te pāmahana i roto i te Kelvin te \( T \) (hei tauira, 298 K),
– Ko te \( n \) te maha o ngā mole o ngā irahiko i whakawhitia,
– Ko te pūmau o Faraday (96485 C/mol) te \( F \),
– Ko te haurua tauhohenga te \( Q \).
Tauhohenga pūtau:
\[
\text{Zn} \rightarrow \text{Zn}^{2+} + 2 \text{e}^- \quad (anode)
\]
\[
\text{Ag}^{+} + \text{e}^- \rightarrow \text{Ag} \quad (katode)
\]
Muri iho, tuhia te tauhohenga katoa:
\[
\kāhua{Zn} + 2\kāhua{Ag}^{+} \rightarrow \kāhua{Zn}^{2+} + 2\kāhua{Ag}
\]
Kia mōhio koe ko n=2 (e rua ngā irahiko i whakawhitia). Tātaihia te uara o \( Q \):
\[
Q = \frac{[\text{Zn}^{2+}]}{[\text{Ag}^+]^2} = \frac{0.01}{(0.1)^2} = \frac{0.01}{0.01} = 1
\]
Nā te mea ko te whārite Nernst te mea \(\ln 1 = 0\), koia te whārite Nernst:
\[
E = E^\circ – \frac{RT}{nF} \ln Q = E^\circ
\]
nō reira, me tatau noa e tātou te \( E^\circ \) mai i te pūmanawa paerewa:
\[
E_{\kākau{pūtau}}^\circ = E_{\kākau{katode}}^\circ – E_{\kākau{anode}}^\circ
= 0.80 \text{ V} – (-0.76 \text{ V})
= 0.80 \text{ V} + 0.76 \text{ V}
= 1.56 \text{ V}
\]
Nō reira, ko te pūmanawa pūtau i raro i ngā āhuatanga kore-paerewa e noho tonu ana ki te 1.56 V nā te mea ko te \(\ln Q\) he kore.
Whakamutunga
He pūkenga nui te ine i te pūmanawa hiko i roto i te matū, inā koa mō ngā tono hiko. Mā te mārama ki ngā ariā taketake pēnei i te pūmanawa paerewa, te whakamahinga o ngā hiko tohutoro, me te tono o te whārite Nernst, ka taea e tātou te whakaoti rapanga maha e pā ana ki te ine i te pūmanawa hiko. Mā ngā tauira pēnei i ngā mea kua kōrerohia ka whakaratohia he tirohanga whānui o te tukanga me ngā mahi e hiahiatia ana hei whakatau i te pūmanawa pūtau i raro i ngā āhuatanga paerewa me ngā āhuatanga kore-paerewa. Ko te tumanako, ka āwhina tēnei tuhinga i a koe ki te mārama me te whakamahi i te ariā o te ine i te pūmanawa hiko i roto i ngā taiwhanga hiko.
