I-enthalpy ne-calorimetry: ukulinganisa ukushisa kokusabela

Ukudweba umkhawulo phakathi kwesistimu nezindawo ezizungezile

Wonke ukubala kwamandla kuqala ngokukhetha isistimu, ngokuvamile amakhemikhali asabelayo. Konke okunye kuyizindawo ezizungezile, ku-calorimeter ezisho ikakhulukazi amanzi noma isixazululo nesitsha. Amandla angawela umkhawulo njengokushisa, q, noma njengomsebenzi, w, futhi ushintsho emandleni angaphakathi esistimu ngu-ΔU = q + w.

I-enthalpy, H = U + PV, ichazwa ukuze ushintsho lwayo lulingane nokushisa okushintshiwe ezingcindezini ezingaguquki lapho umsebenzi kuphela umsebenzi wokunwebeka: ΔH = q_p. Ngoba ikhemistri eningi yetafula yenzeka cishe ezingcindezini ezingaguquki zomkhathi, osokhemisi bakhetha i-enthalpy kunamandla angaphakathi.

Izivumelwano zezimpawu zokushisa ne-enthalpy

Izimpawu zihlala zibhalwa ngokubuka kwesistimu. Ukushisa okugelezela esistimini kuhle; ukushisa okuphuma kubi. Ukusabela kwe-exothermic kukhulula ukushisa ezindaweni ezizungezile, ngakho u-ΔH wako mubi futhi izindawo ezizungezile ziyashisa. Ukusabela kwe-endothermic kumunya ukushisa, ngakho u-ΔH wako muhle futhi izindawo ezizungezile ziyaphola.

Ku-calorimeter ulinganisa izindawo ezizungezile, hhayi ukusabela. Uma amanzi eshisa, amanzi azuze ukushisa, futhi ukusabela kulahlekelwe ngokufanayo. Lokhu kunikeza ubudlelwano obuyinhloko be-calorimetry: q_reaction = −q_surroundings.

I-heat capacity nesibalo u-q = mcΔT

Ukushisa okudingekayo ukushintsha izinga lokushisa lento ngu-q = mcΔT, lapho u-m eyisisindo, u-c ukushisa okuqondene (ukushisa okudingekayo ukufudumeza igremu elilodwa ngedigri eyodwa), no-ΔT = T_final − T_initial. Ushintsho lwedigri eyodwa ye-Celsius lulingana noshintsho lwe-kelvin eyodwa, ngakho u-ΔT unenani elifanayo kunoma yisiphi isikali. Ukushisa okuqondene okusetshenziswe ngezansi kuvela kuTafula 5.1 le-OpenStax Chemistry 2e, kulinganiswe eduze no-25 °C; kumanzi oketshezi, c = 4.184 J/(g·°C).

Isibonelo esisebenzile 1. Kudingeka ukushisa okungakanani ukukhulisa ibhlokhi ye-silicon engu-310.0 g isuka ku-24.5 °C iye ku-160.0 °C? Ukushisa okuqondene kwe-silicon ngu-0.712 J/(g·°C). ΔT = 160.0 − 24.5 = 135.5 °C. q = (310.0 g)(0.712 J/(g·°C))(135.5 °C) = 2.99 × 10⁴ J, noma 29.9 kJ. Ukushisa okuqondene kunezinombolo ezibalulekile ezintathu, ngakho nempendulo inazo.

Isibonelo esisebenzile 2. Ibhlokhi ye-lead engu-450.0 g ku-88.0 °C ifakwa ku-60.0 g wamanzi ku-20.5 °C enkomishini yesiponji. Ukushisa okuqondene kwe-lead ngu-0.130 J/(g·°C), futhi kwamanzi kuyinani elinikeziwe ngenhla. Ukushisa okulahlwe yi-lead kulingana nokushisa okuzuziwe ngamanzi, ngakho q_lead + q_water = 0: (58.5 J/°C)(T_f − 88.0) + (251.0 J/°C)(T_f − 20.5) = 0, lapho isici ngasinye siyisisindo esiphindaphindwe ukushisa okuqondene. Ukuxazulula, T_f = (58.5 × 88.0 + 251.0 × 20.5)/(58.5 + 251.0) = 33.3 °C. Hlola: amanzi azuza cishe 251.0 × 12.8 ≈ 3.2 kJ, futhi i-lead ilahlekelwa cishe 58.5 × 54.7 ≈ 3.2 kJ. Izinga lokushisa lamanzi lihamba kancane kakhulu kunelika-lead ngoba i-heat capacity yawo ngaphezu kwezikhathi ezine ngaphezulu.

I-calorimetry yenkomishi yekhofi ezingcindezini ezingaguquki

I-calorimeter yenkomishi yekhofi iyinkomishi evikelwe ivuleke emoyeni, ngakho inqubo yenzeka ezingcindezini ezingaguquki futhi ukushisa okulinganisiwe kunikeza u-ΔH ngqo. Ezixazululweni zamanzi ezihlanjululiwe, izicabango ezivamile ukuthi isixazululo sinokuminyana nokushisa okuqondene kwamanzi nokuthi inkomishi imunya ukushisa okuncane kakhulu.

Isibonelo esisebenzile 3. U-60.0 mL we-nitric acid engu-0.800 mol/L ku-21.42 °C uxutshwa no-60.0 mL we-potassium hydroxide engu-0.800 mol/L ezingeni lokushisa elifanayo. Ingxube ifinyelela ku-26.75 °C. Thola u-ΔH ngemole ngayinye yamanzi akhiwe. Isisindo sesixazululo: 120.0 mL × 1.00 g/mL = 120. g. ΔT = 26.75 − 21.42 = 5.33 °C. q_solution = (120. g)(4.184 J/(g·°C))(5.33 °C) = 2.68 × 10³ J. Ngakho q_reaction = −2.68 × 10³ J.

Ama-mole amanzi akhiwe: isixazululo ngasinye sinikeza u-0.0600 L × 0.800 mol/L = 0.0480 mol, futhi ukusabela H⁺(aq) + OH⁻(aq) → H₂O(l) kungu-1:1, ngakho akheka u-0.0480 mol wamanzi. ΔH = −2.68 kJ / 0.0480 mol = −55.8 kJ/mol. Njengokuhlola, ama-enthalpy ajwayelekile okwakheka avela kuSithasiselo G se-OpenStax anikeza −285.83 − (−230.0) = −55.8 kJ/mol kusibalo esifanayo se-ayoni esicwengiwe, kuthathwa u-ΔH°f ka-H⁺(aq) njengo-zero ngesivumelwano.

I-bomb calorimetry nomehluko phakathi kuka-ΔU no-ΔH

Ukushisa kulinganiswa ku-bomb calorimeter, isitsha sensimbi esivaliwe emanzini okugeza. Ngoba ivolumu imisiwe, akukho msebenzi wokunwebeka owenziwayo futhi ukushisa okulinganisiwe kungu-ΔU, hhayi u-ΔH. Wonke amathuluzi alinganiswa njengeyunithi eyodwa, kunikeza isilinganiso se-calorimeter C_cal nge-kJ/°C, ngakho q = C_cal × ΔT ngaphandle kwesisindo esihlukile noma ukushisa okuqondene.

Isibonelo esisebenzile 4. Ukushisa u-0.5000 g we-benzene eketshezi, C₆H₆, ku-calorimeter ene-C_cal = 10.25 kJ/°C kukhulisa izinga lokushisa ngo-2.038 °C. Ngezisindo ze-athomu ezijwayelekile ze-IUPAC eziyiswe emadesimalini amabili (C 12.01, H 1.01), M = 78.12 g/mol, ngakho n = 0.5000 g / 78.12 g/mol = 0.006400 mol. q_cal = (10.25 kJ/°C)(2.038 °C) = 20.89 kJ, ngakho ΔU = −20.89 kJ / 0.006400 mol = −3264 kJ/mol, ngezinombolo ezibalulekile ezine ngoba wonke amanani alinganisiwe anezine.

Ukuguqulela ku-enthalpy, sebenzisa u-ΔH = ΔU + Δn_gas RT. Ku-C₆H₆(l) + 15/2 O₂(g) → 6 CO₂(g) + 3 H₂O(l), ama-mole egesi ehla asuka ku-7.5 aye ku-6, ngakho Δn_gas = −1.5 futhi ukulungisa kungu-(−1.5)(8.314 J/(mol·K))(298.15 K) = −3.72 kJ/mol. ΔH = −3264 − 3.72 = −3268 kJ/mol, kuhambisana no-−3267.7 kJ/mol otholwe kuma-enthalpy okwakheka kuSithasiselo G. Ukulungisa kukhula lapho ukusabela kwakha noma kudla ama-mole amaningi egesi.

Ukufunda nokukalisa izibalo ze-thermochemical

Isibalo se-thermochemical sinamathisela u-ΔH ekusabeleni kanye njengoba kubhaliwe. Phindaphinda kabili izinombolo ezandulelayo futhi u-ΔH uphindeke kabili; phendula ukusabela futhi uphawu luyashintsha. Izimo zenyama ziyabaluleka: ukwakha amanzi oketshezi kukhulula ukushisa okuningi kunokwakha umhwamuko wamanzi, ngoba ukufingqeka ngokwako kuyi-exothermic.

Ukuthola ukushisa kwenani elithile lento, guqula kube ama-mole bese usebenzisa u-ΔH ngemole ngayinye yokusabela njengesici sokuguqula. Ukushisa u-12.5 g we-benzene, ngo-ΔH = −3267.7 kJ ngemole ngayinye ye-benzene, kukhulula (12.5 g / 78.12 g/mol) × 3267.7 kJ/mol = 523 kJ. Kubhale njengo-q = −523 kJ wokusabela, noma njengo-523 kJ wokushisa okukhululwayo.

Amaphutha e-calorimetry aphendula izimpawu noma alahlekelwa ukushisa

Izibalo ze-calorimetry zimfushane, ngakho amaphutha amaningi angawomqondo.

Ukuhlola kokugcina okuthembekile kungokwenyama: uma amanzi eshise, ukusabela kufanele kube ne-ΔH embi.

• Uphawu lokususa olungekho: izinga lokushisa lezindawo ezizungezile lenyuke, ngakho u-q_reaction mubi. Ukubika u-+55.8 kJ/mol ekuthuliseni okufudumeze amanzi iphutha lophawu.
• Isisindo esingalungile: ku-calorimetry yesixazululo, sebenzisa isisindo sesixazululo sonke, hhayi i-solute kuphela noma enye yamavolumu amabili axutshiwe.
• Ngegremu uma kuqhathaniswa ngemole: hlukanisa ngama-mole ohlobo oluchaziwe ukuthola kJ/mol, futhi usho ukuthi yiluphi uhlobo.
• Ukuxuba ama-joule nama-kilojoule: u-q ovela ku-mcΔT ungama-joule; guqula ngaphambi kokuhlukanisa ube impendulo ye-kJ/mol.
• Ukuthatha idatha ye-bomb njengo-ΔH: i-bomb evaliwe inikeza u-ΔU; sebenzisa ukulungisa u-Δn_gas RT lapho u-ΔH edingeka.