I-entropy ne-Gibbs free energy: ukubikezela ukuthi inqubo iya ngakuphi

Okuzenzakalelayo kusho okuvunyelwe yi-thermodynamics, hhayi okusheshayo

Inqubo ezenzakalelayo yileyo okuthi, uma isiqalile, iqhubeke ngaphandle kokufakwa njalo kwamandla avela ngaphandle. Ukugqwala kwe-iron nokugeleza kokushisa kusuka entweni eshisayo kuya kebandayo kuyazenzakalela. Okuphambene nakho akuzenzakaleli: ukugqwala akuphenduki kube yi-iron ngokwakho.

Ukuzenzakalela akusho lutho ngejubane. Idayimane eliguquka libe yi-graphite ezingeni lokushisa legumbi kuyazenzakalela, kodwa kuhamba kancane kangangokuthi amadayimane ahlala unomphela. I-thermodynamics ikutshela ukuthi iyiphi indlela eyehlela phansi. I-kinetics ikutshela ukuthi isistimu ifika lapho ngokushesha kangakanani.

Izinqubo eziningi ezizenzakalelayo zikhulula ukushisa, kodwa hhayi zonke. Ukuncibilika kweqhwa ngaphezu kuka-0 °C, ukuhwamuka kwamanzi nokuncibilika kwe-ammonium nitrate konke kuyi-endothermic futhi kusazenzakalela. Kukhona okunye ngaphandle kwe-enthalpy okubandakanyekayo, futhi lokho yi-entropy.

I-entropy ibala izindlela amandla angasakazeka ngazo

I-entropy, S, ilinganisa ukuthi mangaki amalungiselelo amancane kakhulu (ama-microstate) ahambisana nesimo esibonwayo sesistimu. Ubudlelwano buka-Boltzmann ngu-S = k ln W, lapho u-W eyinani lama-microstate no-k eyi-Boltzmann constant. Inkululeko eyengeziwe yokunyakaza nezindawo eziningi zokubeka amandla kusho ama-microstate amaningi ne-entropy ephakeme.

Umthetho wesithathu we-thermodynamics uthi i-crystal ephelele ku-0 K ine-entropy eyi-zero. Lokho kunikeza i-entropy iphuzu le-zero eliphelele, ngakho amatafula abhala ama-entropy e-molar ajwayelekile aphelele, S°, hhayi ama-entropy okwakheka. Ngokungafani no-ΔH°f, u-S° wesakhi akayona i-zero: uSithasiselo G we-OpenStax unikeza u-130.7 J/(mol·K) we-H₂(g) no-205.2 J/(mol·K) we-O₂(g).

Ngokuvamile ungabikezela uphawu luka-ΔS ngaphambi kokulubala:

• Amagesi ane-entropy eningi kakhulu kunoketshezi, noketshezi lunengaphezulu kunezinto eziqinile. USithasiselo G ubhala u-70.0 J/(mol·K) we-H₂O(l) no-188.8 J/(mol·K) we-H₂O(g).
• Ukusabela okwandisa inani lama-mole egesi ngokuvamile kuno-ΔS omuhle. Okulinciphisayo ngokuvamile kuno-ΔS omubi.
• Ukukhuphula izinga lokushisa lento kukhuphula i-entropy yayo.
• Ukuncibilikisa into eqinile oketshezini ngokuvamile kwandisa i-entropy, nakuba ama-ayoni ahlela kakhulu amanzi azungezile angakuphendula lokhu.

Ukubala u-ΔS° nokusebenzisa umthetho wesibili

Ushintsho lwe-entropy olujwayelekile lokusabela lulandela iphethini efanayo nomthetho ka-Hess: ΔS° = Σ n S°(imikhiqizo) − Σ m S°(izisabelo), kusetshenziswa ama-coefficient esibalo esilinganisiwe.

Isibonelo esisebenzile 1. Ku-N₂(g) + 3 H₂(g) → 2 NH₃(g), uSithasiselo G unikeza u-S° = 191.6 we-N₂, 130.7 we-H₂ no-192.8 we-NH₃, konke ngo-J/(mol·K). ΔS° = 2(192.8) − [191.6 + 3(130.7)] = 385.6 − 583.7 = −198.1 J/K. Uphawu olubi luhambisana nokubikezela, ngoba ama-mole amane egesi aba mabili.

U-ΔS omubi wesistimu awukukhiphi ukusabela okuzenzakalelayo. Umthetho wesibili uthi i-entropy yendawo yonke iyakhula kuyo yonke inqubo ezenzakalelayo: ΔS_univ = ΔS_sys + ΔS_surr > 0. Ukushisa okukhululelwa ezindaweni ezizungezile kukhuphula i-entropy yazo ngo-ΔS_surr = −ΔH_sys/T. USithasiselo G unikeza u-ΔH° = 2(−45.9) = −91.8 kJ walokhu kusabela. Ku-298.15 K, ΔS_surr = +91 800 J ÷ 298.15 K = +307.9 J/K. ΔS_univ = −198.1 + 307.9 = +109.8 J/K, okuhle, ngakho ukusabela kuyazenzakalela ngaphansi kwezimo ezijwayelekile ku-25 °C.

I-Gibbs free energy nezinhlanganisela ezine zezimpawu

Ukulandelela izindawo ezizungezile ngokwehlukana kunzima. Ukuphindaphinda u-ΔS_univ ngo-−T kunikeza inani elincike esistimini kuphela: ushintsho lwe-Gibbs free energy, ΔG = ΔH − TΔS. Ezingeni lokushisa nengcindezi engaguquki, inqubo iyazenzakalela lapho u-ΔG emubi, isekulinganeni lapho u-ΔG eyi-zero, futhi ayizenzakaleli lapho u-ΔG emuhle.

Isibonelo esisebenzile 2. Ekwakhiweni kwe-ammonia ku-298.15 K, ΔG° = −91.8 kJ − (298.15 K)(−0.1981 kJ/K) = −32.7 kJ. Qaphela ukuguqulwa kuka-ΔS kusuka ku-J/K kuya ku-kJ/K. USithasiselo G ubhala nama-free energy okwakheka, futhi 2 × ΔG°f(NH₃) = 2(−16.5) = −33.0 kJ. Lezi zindlela ezimbili ziyavumelana ngaphakathi kokuyisa kwamanani asetafuleni. U-−32.7 kJ ofanayo ulingana no-−T × ΔS_univ wesibonelo 1.

Ngoba u-T uhlala emuhle, izimpawu zika-ΔH no-ΔS zinquma iphethini:

• ΔH omubi, ΔS omuhle: kuyazenzakalela kuwo wonke amazinga okushisa.
• ΔH omuhle, ΔS omubi: akuzenzakaleli kunoma yiliphi izinga lokushisa.
• ΔH omubi, ΔS omubi: kuyazenzakalela ngaphansi kwezinga lokushisa lokushintsha T = ΔH/ΔS. Ukwakhiwa kwe-ammonia kukuleli qembu, no-T = −91 800 J ÷ −198.1 J/K = 463 K, cishe 190 °C.
• ΔH omuhle, ΔS omuhle: kuyazenzakalela ngaphezu kwezinga lokushisa lokushintsha. Ukuncibilika nokubila kukuleli qembu.

Isibonelo esisebenzile: kungani amanzi ebila eduze no-100 °C

Ku-H₂O(l) → H₂O(g), uSithasiselo G unikeza u-ΔH° = −241.82 − (−285.83) = +44.01 kJ no-ΔS° = 188.8 − 70.0 = +118.8 J/K. Izinga lokushisa lokushintsha lingu-44 010 J ÷ 118.8 J/K = 370 K, noma cishe 97 °C. Indawo yokubila evamile elinganisiwe ingu-373 K. Igebe elincane livela ngoba u-ΔH no-ΔS bobabili bashintsha ngezinga lokushisa, kanti lokhu kulinganisela kusebenzisa amanani abo aku-25 °C. Noma kunjalo, idatha elinganiswe ku-25 °C ibikezela indawo yokubila ngaphakathi kuka-3 K cishe.

Ku-25 °C, ΔG° = −228.59 − (−237.1) = +8.51 kJ, okuhle. Kodwa amanzi ashiywe esitsheni esivulekile ayahwamuka. Isixazululo siwukuthi u-ΔG° ubhekisela ezimweni ezijwayelekile, lapha umhwamuko wamanzi ku-1 bar. Ushintsho lwangempela lwe-free energy luncike engcindezini yangempela yomhwamuko ngo-ΔG = ΔG° + RT ln Q. Uma umoya uphethe umhwamuko wamanzi ku-0.0100 bar, Q = 0.0100 futhi ΔG = 8.51 kJ + (8.314 × 10⁻³ kJ/(mol·K))(298.15 K) ln(0.0100) = 8.51 − 11.42 = −2.91 kJ/mol. Ukuhwamuka kuyazenzakalela ngaphansi kwalezo zimo.

Kusuka ku-ΔG° kuya ekungaguqukini kokulingana

Ekulinganeni ΔG = 0 no-Q = K, ngakho ΔG° = −RT ln K, noma K = e^(−ΔG°/RT). U-ΔG° omubi unikeza u-K omkhulu kuno-1, okusho ukuthi imikhiqizo iyathandwa ekulinganeni. U-ΔG° omuhle unikeza u-K ongaphansi kuka-1. Ngoba ubudlelwano buyi-exponential, ushintsho olucishe lube ngu-5.7 kJ/mol ku-ΔG° lushintsha u-K ngokuphindwe kayishumi ku-25 °C.

Isibonelo esisebenzile 3. Ekubeni umhwamuko kwamanzi ku-25 °C, K = exp[−8510 ÷ (8.314 × 298.15)] = 0.0323. Lapha u-K uyingcindezi yomhwamuko yokulingana ngo-bar, okungu-24.2 torr. Itafula 9.2 le-OpenStax libhala u-23.8 torr olinganisiwe ku-25 °C. Ukusondela kangaka kusuka kudatha ye-thermodynamic esetafuleni kuphela kuwukuhlola okuqinile kokuthi indlela iyasebenza.

Isibonelo esisebenzile 4. Ekwakhiweni kwe-ammonia, K = exp[−(−33 000) ÷ (8.314 × 298.15)] ≈ 6 × 10⁵ ku-25 °C. Bika u-K ngezinombolo ezibalulekile eyodwa noma ezimbili kuphela. Ukungaqiniseki kuka-0.1 kJ ku-ΔG° sekuvele kushintsha u-K ngamaphesenti angu-4 cishe.

Amaphutha ophawu, amayunithi nesimo esijwayelekile

Amaphutha amaningi ezinkingeni ze-free energy avela kumayunithi nasekudideni izimo ezijwayelekile nezangempela. Bhala amayunithi kuyo yonke ingxenye futhi uhlole ukuthi uphawu lomphumela ngamunye luhambisana nokubikezela kwakho.

• Ukuhlanganisa u-ΔH ngo-kJ no-ΔS ngo-J/K ngaphandle kokuguqula. Hlukanisa u-ΔS ngo-1000 kuqala.
• Ukusebenzisa izinga lokushisa le-Celsius. U-T ku-ΔG = ΔH − TΔS naku-RT ln K kufanele abe ngama-kelvin.
• Ukubeka u-S° wesakhi ku-zero. U-ΔH°f no-ΔG°f kuphela abangu-zero ezakhini ezisemafomini azo esikhombisi.
• Ukuthatha u-ΔG° no-ΔG njengento efanayo. U-ΔG° ukutshela ngezimo ezijwayelekile futhi unquma u-K; u-ΔG unquma okwenzekayo ngaphansi kwezimo zangempela.
• Ukuphetha ngokuthi ukusabela okuno-ΔG omubi kufanele kushese.
• Ukusebenzisa u-R = 0.08206 L·atm/(mol·K) ezibalweni zamandla. Sebenzisa u-8.314 J/(mol·K).