Piv txwv ntawm Cov Lus Nug Sib Tham Txog Electrochemistry
Electrochemistry yog ib ceg ntawm chemistry uas kawm txog kev sib raug zoo ntawm cov tshuaj lom neeg thiab kev hloov pauv ntawm lub zog hluav taws xob. Hauv electrochemistry, muaj ob lub tswv yim tseem ceeb: oxidation (kev tso tawm ntawm cov electrons) thiab kev txo qis (qhov nce ntawm cov electrons). Cov txheej txheem no tuaj yeem pom hauv ob hom electrochemical cells: voltaic cells (galvanic cells) thiab electrolytic cells. Hauv qab no yog qee qhov piv txwv teeb meem thiab lawv cov lus piav qhia los pab koj nkag siab txog electrochemistry.
Piv txwv lus nug 1: Voltaic Cell
Lo lus nug:
Muab ib lub cell voltaic nrog zinc (Zn) thiab tooj liab (Cu) electrodes txuas nrog los ntawm ib lub choj ntsev. Zn raug muab tso rau hauv 1 M ZnSO4 kua thiab Cu raug muab tso rau hauv 1 M CuSO4 kua. Sau cov tshuaj tiv thaiv uas tshwm sim ntawm txhua lub electrode thiab xam qhov sib txawv ntawm lub zog (EMF) ntawm lub cell voltaic. Cov ntaub ntawv txog lub zog electrode txheem:
\[ E^o_{\text{Zn}^{2+}/\text{Zn}} = -0.76 \, \text{V} \]
\[ E^o_{\text{Cu}^{2+}/\text{Cu}} = +0.34 \, \text{V} \]
Kev Sib Tham:
Kauj ruam thawj zaug yog txiav txim siab qhov kev ua haujlwm redox uas tshwm sim. Hauv lub cell voltaic, qhov kev ua haujlwm redox tshwm sim qhov twg
- Zinc (Zn) raug oxidation:
\[ \text{Zn (s)} \rightarrow \text{Zn}^{2+} (aq) + 2e^- \]
- Tooj liab (Cu) raug txo qis:
\[ \text{Cu}^{2+} (aq) + 2e^- \rightarrow \text{Cu (s)} \]
Tag nrho cov tshuaj redox hauv lub cell voltaic yog:
\[ \text{Zn (s)} + \text{Cu}^{2+} (aq) \rightarrow \text{Zn}^{2+} (aq) + \text{Cu (s)} \]
Tom ntej no, peb yuav xam qhov sib txawv ntawm lub cell:
\[ E_{\text{cell}} = E^o_{\text{cathode}} – E^o_{\text{anode}} \]
Qhov twg:
- Lub cathode yog lub electrode qhov twg txo qis (Cu) tshwm sim.
- Lub anode yog lub electrode qhov twg oxidation (Zn) tshwm sim.
Yog li ntawd,
\[ E_{\text{sel}} = 0.34 \, \text{V} – (-0.76 \, \text{V}) \]
\[ E_{\text{sel}} = 0.34 \, \text{V} + 0.76 \, \text{V} = 1.10 \, \text{V} \]
Kesimpulan:
- Cov tshuaj tiv thaiv uas tshwm sim ntawm qhov anode (Zn):
\[ \text{Zn (s)} \rightarrow \text{Zn}^{2+} (aq) + 2e^- \]
- Cov tshuaj tiv thaiv uas tshwm sim ntawm cathode (Cu):
\[ \text{Cu}^{2+} (aq) + 2e^- \rightarrow \text{Cu (s)} \]
- Qhov sib txawv ntawm lub hlwb (EMF): 1.10 V
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Piv txwv lus nug 2: Electrolytic Cell
Lo lus nug:
Hauv kev electrolysis ntawm NaCl kua, hais txog cov tshuaj tiv thaiv uas tshwm sim ntawm cathode thiab anode yog tias siv lub inert electrode, xws li platinum (Pt),. Xam tag nrho cov nqi uas xav tau los tsim 1 gram ntawm Cl2. (Ar Cl = 35.5)
Kev Sib Tham:
Kauj ruam thawj zaug yog sau cov tshuaj tiv thaiv uas tshwm sim ntawm txhua lub electrode hauv cov kua ntsev NaCl.
- Ntawm lub cathode (kev txo qis):
Hauv cov txheej txheem no, H+ ions los ntawm dej yuav raug txo qis:
\[ 2H_2O(l) + 2e^- \rightarrow H_2(g) + 2OH^-(aq) \]
- Ntawm qhov anode (oxidation):
Cov Cl-ion yuav dhau los ua oxidation los ua Cl2 roj:
\[ 2Cl^-(aq) \rightarrow Cl_2(g) + 2e^- \]
Tag Nrho Cov Kev Tshwm Sim:
Yog li tag nrho cov tshuaj tiv thaiv uas tshwm sim hauv electrolysis ntawm NaCl kua yog:
\[ 2NaCl(aq) + 2H_2O(l) \rightarrow 2NaOH(aq) + H_2(g) + Cl_2(g) \]
Yuav kom xam tau tus nqi uas yuav tsum tau los tsim 1 gram ntawm Cl2, peb yuav tsum txiav txim siab seb muaj pes tsawg moles ntawm Cl2:
\[ \text{Qhov hnyav ntawm Cl}_2 = 1 \text{ gram} \]
\[ \text{ArCl}_2 = 2 \times 35.5 = 71 \text{ gram/mol} \]
\[ \text{Tus lej ntawm moles ntawm Cl}_2 = \frac{1}{71} \text{ mol} \]
Raws li qhov sib npaug ntawm cov tshuaj tiv thaiv ntawm qhov anode, 1 mol ntawm Cl2 yog tsim los ntawm 2 mol ntawm cov electrons:
\[ 2Cl^- \rightarrow Cl_2 + 2e^- \]
Hauv lwm lo lus, 1 mole ntawm Cl2 xav tau 2 moles ntawm electrons.
Tus naj npawb ntawm moles ntawm electrons:
\[ \text{Tus naj npawb ntawm moles ntawm electrons} = 2 \times \frac{1}{71} = \frac{2}{71} \text{ mol} \]
Tus nqi uas yuav tsum tau them tuaj yeem suav tau siv tus nqi Faraday (F = 96485 C/mol e^-):
\[ Q = n \times F \]
\[ Q = \left(\frac{2}{71} \text{ mol}\right) \times 96485 \text{ C/mol} \]
\[ Q = 2718 \text{ C} \]
Kesimpulan:
- Kev cuam tshuam ntawm cathode:
\[ 2H_2O(l) + 2e^- \rightarrow H_2(g) + 2OH^-(aq) \]
- Kev cuam tshuam ntawm anode:
\[ 2Cl^-(aq) \rightarrow Cl_2(g) + 2e^- \]
- Tag nrho cov nqi uas yuav tsum tau los tsim 1 gram ntawm Cl2 yog 2718 C.
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Piv txwv 3: Kev Sib Raug Zoo ntawm Nernst thiab Cov Xwm Txheej Tsis Yog Tus Qauv
Lo lus nug:
Xam lub peev xwm ntawm lub cell voltaic ua los ntawm Ag/Ag+ electrodes nrog lub concentration ntawm cov nyiaj ion ntawm 0.1 M thiab Zn/Zn2+ electrodes nrog lub concentration ntawm 0.01 M. Lub peev xwm electrode txheem yog:
\[ E^o_{\text{Ag}^{+}/\text{Ag}} = +0.80 \, \text{V} \]
\[ E^o_{\text{Zn}^{2+}/\text{Zn}} = -0.76 \, \text{V} \]
Kev Sib Tham:
Kauj ruam thawj zaug yog sau cov kev tshuaj tiv thaiv uas tshwm sim:
- Oxidation ntawm lub anode (Zn):
\[ \text{Zn (s)} \rightarrow \text{Zn}^{2+} (aq) + 2e^- \]
- Kev txo qis ntawm cathode (Ag):
\[ \text{Ag}^{+} (aq) + e^- \rightarrow \text{Ag (s)} \]
Tag nrho cov kev teb:
\[ \text{Zn (s)} + 2\text{Ag}^{+} (aq) \rightarrow \text{Zn}^{2+} (aq) + 2\text{Ag (s)} \]
Raws li qhov sib npaug ntawm Nernst:
\[ E_{\text{Cell}} = E^o_{\text{Cell}} – \left( \frac{0.0592}{n} \right) \log \left( \frac{[\text{product}]}{[\text{reactant}]} \right) \]
Qhov twg:
\[ n = 2 \]
Ua ntej, xam E^o_{\text{Sel}}:
\[ E^o_{\text{Sel}} = E^o_{\text{Ag}^{+}/\text{Ag}} – E^o_{\text{Zn}^{2+}/\text{Zn}} \]
\[ E^o_{\text{Sel}} = 0.80 \, \text{V} – (-0.76 \, \text{V}) \]
\[ E^o_{\text{Cell}} = 1.56 \, \text{V} \]
Tom ntej no, xam qhov tseeb ntawm lub cell muaj peev xwm ntawm qhov concentration uas tau muab:
\[ E_{\text{Sel}} = 1.56 \, \text{V} – \left( \frac{0.0592}{2} \right) \log \left( \frac{[\text{Zn}^{2+}]}{[\text{Ag}^{+}]^2} \right) \]
\[ E_{\text{Sel}} = 1.56 \, \text{V} – \left( \frac{0.0592}{2} \right) \log \left( \frac{0.01}{(0.1)^2} \right) \]
\[ E_{\text{Sel}} = 1.56 \, \text{V} – 0.0296 \log \left( \frac{0.01}{0.01} \right) \]
\[ E_{\text{Cell}} = 1.56 \, \text{V} \]
Kesimpulan:
- Cov tshuaj tiv thaiv uas tshwm sim ntawm qhov anode thiab cathode tseem zoo li qub
- Lub peev xwm ntawm lub cell nrog qhov concentration yog 1.56 V
Tsab xov xwm no qhia txog yuav ua li cas daws ntau hom teeb meem hauv electrochemistry, suav nrog cov teeb meem cuam tshuam nrog voltaic cells, electrolytic cells, thiab kev suav siv Nernst Equation. Kev nkag siab zoo txog cov ntsiab cai tom qab redox reactions thiab lub peev xwm siv cov ntaub ntawv electrochemical yog qhov tseem ceeb rau kev vam meej hauv kev daws cov teeb meem no.
