Laʻana o nā nīnau kūkākūkā electrochemistry
ʻO ka electrochemistry kahi lālā o ke kemika e aʻo ana i ka pilina ma waena o nā hopena kemika a me nā loli o ka ikehu uila. I loko o ka electrochemistry, aia ʻelua mau manaʻo nui: ka oxidation (ka hoʻokuʻu ʻana o nā electrons) a me ka hōʻemi (ka loaʻa ʻana o nā electrons). Hiki ke ʻike ʻia kēia mau kaʻina hana i ʻelua ʻano o nā cell electrochemical: nā cell voltaic (nā cell galvanic) a me nā cell electrolytic. Aia ma lalo iho kekahi mau pilikia hoʻohālike a me kā lākou wehewehe ʻana e kōkua iā ʻoe e hoʻomaopopo i ka electrochemistry.
Laʻana Nīnau 1: Kelepona Voltaic
Nīnau:
Hāʻawi ʻia kahi cell voltaic me nā electrodes zinc (Zn) a me ke keleawe (Cu) i hoʻopili ʻia ma o kahi alahaka paʻakai. Hoʻoluʻu ʻia ʻo Zn i loko o kahi hopena 1 M ZnSO4 a hoʻoluʻu ʻia ʻo Cu i loko o kahi hopena 1 M CuSO4. E kākau i lalo i nā hopena e kū mai ana ma kēlā me kēia electrode a helu i ka ʻokoʻa potential (EMF) o ka cell voltaic. ʻIkepili potential electrode maʻamau:
\[ E^o_{\text{Zn}^{2+}/\text{Zn}} = -0.76 \, \text{V} \]
\[ E^o_{\text{Cu}^{2+}/\text{Cu}} = +0.34 \, \text{V} \]
Kūkākūkā:
ʻO ka hana mua, ʻo ia ke hoʻoholo i ka hopena redox e hana ʻia ana. I loko o kahi cell voltaic, hana ʻia kahi hopena redox spontaneous kahi e hana ai
– Hoʻopilikia ʻia ka Zinc (Zn):
\[ \text{Zn (s)} \rightarrow \text{Zn}^{2+} (aq) + 2e^- \]
– Hoʻemi ʻia ke keleawe (Cu):
\[ \text{Cu}^{2+} (aq) + 2e^- \polokau \text{Cu (s)} \]
ʻO ka hopena redox holoʻokoʻa i loko o kahi cell voltaic penei:
\[ \text{Zn (s)} + \text{Cu}^{2+} (aq) \rightarrow \text{Zn}^{2+} (aq) + \text{Cu (s)} \]
A laila, e helu mākou i ka ʻokoʻa hiki o ke kelepona:
\[ E_{\text{cell}} = E^o_{\text{cathode}} – E^o_{\text{anode}} \]
Ma hea:
– ʻO ke cathode ka electrode kahi e hana ʻia ai ka hōʻemi (Cu).
– ʻO ke anode ka electrode kahi e hana ʻia ai ka oxidation (Zn).
No laila,
\[ E_{\text{sel}} = 0.34 \, \text{V} – (-0.76 \, \text{V}) \]
\[ E_{\text{sel}} = 0.34 \, \text{V} + 0.76 \, \text{V} = 1.10 \, \text{V} \]
Ka hopena:
– ʻO ka hopena e kū mai ana ma ka anode (Zn):
\[ \text{Zn (s)} \rightarrow \text{Zn}^{2+} (aq) + 2e^- \]
– ʻO ka hopena e kū mai ana ma ka cathode (Cu):
\[ \text{Cu}^{2+} (aq) + 2e^- \polokau \text{Cu (s)} \]
– ʻOkoʻa hiki ke kelepona (EMF): 1.10 V
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Laʻana Nīnau 2: Kelepona Electrolytic
Nīnau:
I ka electrolysis o kahi hopena NaCl, e haʻi i nā hopena e kū mai ana ma ka cathode a me ka anode inā hoʻohana ʻia kahi electrode inert, e like me ka platinum (Pt). E helu i ka uku holoʻokoʻa e pono ai e hana i 1 gram o Cl2. (Ar Cl = 35.5)
Kūkākūkā:
ʻO ka hana mua, ʻo ia ke kākau i lalo i nā hopena e kū mai ana ma kēlā me kēia electrode i loko o ka hopena paʻakai NaCl.
– Ma ke cathode (hoʻemi):
Ma kēia kaʻina hana, e hoʻemi ʻia nā ion H+ mai ka wai:
\[ 2H_2O(l) + 2e^- \arrow H_2(g) + 2OH^-(aq) \]
– Ma ka anode (oxidation):
E hoʻoheheʻe ʻia ka ion Cl- e lilo i kinoea Cl2:
\[ 2Cl^-(aq) \arrow Cl_2(g) + 2e^- \]
Ka hopena holoʻokoʻa:
No laila, ʻo ka hopena holoʻokoʻa e kū mai ana ma ka electrolysis o ka hopena NaCl penei:
\[ 2NaCl(aq) + 2H_2O(l) \arrow 2NaOH(aq) + H_2(g) + Cl_2(g) \]
No ka helu ʻana i ka uku e pono ai e hana i 1 gram o Cl2, pono mākou e hoʻoholo i ka helu o nā moles o Cl2:
\[ \text{Papa o Cl}_2 = 1 \text{ gram} \]
\[ \text{Ar Cl}_2 = 2 \times 35.5 = 71 \text{ gram/mol} \]
\[ \text{Helu o nā mole o Cl}_2 = \frac{1}{71} \text{ mol} \]
Ma muli o ka hoʻohālikelike hopena ma ka anode, ua hana ʻia he 1 mol o Cl2 mai 2 mol o nā electrons:
\[ 2Cl^- \rightarrow Cl_2 + 2e^- \]
I nā huaʻōlelo ʻē aʻe, pono 1 mole o Cl2 i 2 moles o nā electrons.
Helu o nā mole o nā electrons:
\[ \text{Helu o nā mole o nā electrons} = 2 \times \frac{1}{71} = \frac{2}{71} \text{ mol} \]
Hiki ke helu ʻia ka uku i koi ʻia me ka hoʻohana ʻana i ka waiwai Faraday (F = 96485 C/mol e^-):
\[ Q = n \times F \]
\[ Q = \left(\frac{2}{71} \text{ mol}\right) \times 96485 \text{ C/mol} \]
\[ Q = 2718 \kikokikona{ C} \]
Ka hopena:
– Ka pane ʻana ma ke cathode:
\[ 2H_2O(l) + 2e^- \arrow H_2(g) + 2OH^-(aq) \]
– Ka pane ʻana ma ka anode:
\[ 2Cl^-(aq) \arrow Cl_2(g) + 2e^- \]
ʻO ka huina uku e pono ai e hana i 1 gram o Cl2 he 2718 C.
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Laʻana 3: Pilina Nernst a me nā Kūlana Maʻamau ʻole
Nīnau:
E helu i ka hiki o kahi cell voltaic i hana ʻia mai nā electrodes Ag/Ag+ me ka nui o ka ion kālā he 0.1 M a me nā electrodes Zn/Zn2+ me ka nui o 0.01 M. ʻO ke hiki electrode maʻamau:
\[ E^o_{\text{Ag}^{+}/\text{Ag}} = +0.80 \, \text{V} \]
\[ E^o_{\text{Zn}^{2+}/\text{Zn}} = -0.76 \, \text{V} \]
Kūkākūkā:
ʻO ka hana mua, ʻo ia ke kākau i nā hopena e kū mai ana:
– ʻOkika ma ka anode (Zn):
\[ \text{Zn (s)} \rightarrow \text{Zn}^{2+} (aq) + 2e^- \]
– Ka hōʻemi ʻana ma ke cathode (Ag):
\[ \text{Ag}^{+} (aq) + e^- \rightarrow \text{Ag (s)} \]
Ka hopena holoʻokoʻa:
\[ \text{Zn (s)} + 2\text{Ag}^{+} (aq) \rightarrow \text{Zn}^{2+} (aq) + 2\text{Ag (s)} \]
Ma muli o ka hoʻohālikelike Nernst:
\[ E_{\text{Cell}} = E^o_{\text{Cell}} – \left( \frac{0.0592}{n} \right) \log \left( \frac{[\text{product}]}{[\text{reactant}]} \right) \]
Ma hea:
\[ n = 2 \]
ʻO ka mea mua, e helu iā E^o_{\text{Sel}}:
\[ E^o_{\text{Sel}} = E^o_{\text{Ag}^{+}/\text{Ag}} – E^o_{\text{Zn}^{2+}/\text{Zn}} \]
\[ E^o_{\text{Sel}} = 0.80 \, \text{V} – (-0.76 \, \text{V}) \]
\[ E^o_{\text{Cell}} = 1.56 \, \text{V} \]
A laila, e helu i ka hiki ke loaʻa maoli o ke kelepona ma ka nui i hāʻawi ʻia:
\[ E_{\text{Sel}} = 1.56 \, \text{V} – \left( \frac{0.0592}{2} \right) \log \left( \frac{[\text{Zn}^{2+}]}{[\text{Ag}^{+}]^2} \right) \]
\[ E_{\text{Sel}} = 1.56 \, \text{V} – \left( \frac{0.0592}{2} \right) \log \left( \frac{0.01}{(0.1)^2} \right) \]
\[ E_{\text{Sel}} = 1.56 \, \text{V} – 0.0296 \log \left( \frac{0.01}{0.01} \right) \]
\[ E_{\text{Cell}} = 1.56 \, \text{V} \]
Ka hopena:
– ʻO nā hopena e kū mai ana ma ka anode a me ka cathode e like mau nō ia
– ʻO ka hiki ke hana ʻia o ke kelepona me kahi ʻano i hāʻawi ʻia he 1.56 V
Hōʻike kēia ʻatikala pehea e hoʻoponopono ai i kekahi mau ʻano pilikia i ka electrochemistry, me nā pilikia e pili ana i nā cell voltaic, nā cell electrolytic, a me nā helu ʻana me ka hoʻohana ʻana i ka Nernst Equation. ʻO ka hoʻomaopopo piha ʻana i nā kumumanaʻo ma hope o nā hopena redox a me ka hiki ke hoʻohana i ka ʻikepili electrochemical he mea nui ia no ka holomua i ka hoʻoponopono ʻana i kēia mau ʻano pilikia.
