Lub tshav kub ntawm tag - yog dab tsi no?

Peb tham txog dab tsi yog lub tshav kub ntawm tag, raws li zoo raws li txhais tau lub tej yam kev mob uas hu ua txheej txheem. Nyob rau hauv thiaj li yuav txheeb tawm qhov teeb meem no, nrhiav kom paub cov kev sib txawv ntawm tej yam yooj yim thiab complex tshuaj. Yuav kom sau lub tswvyim ntawm "tshav kub ntawm tag", xav txog cov kev tshuaj kab zauv.

Tus txheem enthalpy ntawm tsim ntawm tshuaj

76 kJ ntawm lub zog tso rau hauv cov tshuaj tiv thaiv ntawm cov pa roj carbon nrog hydrogen gas sis raug zoo. Nyob rau hauv cov ntaub ntawv no, daim duab - yog lub thermal nyhuv ntawm tshuaj cov tshuaj tiv thaiv. Tab sis qhov no tshav kub ntawm tsim ntawm methane molecules los ntawm tej yam yooj yim tshuaj. "Yog vim li cas?" - Koj nug. Qhov no yog vim lub fact tias cov pib Cheebtsam yog cov pa roj carbon thiab hydrogen. 76 kJ / mol yog lub zog uas chemists hu ua "tshav kub ntawm tag".

Cov ntaub ntawv ntawv

Nyob rau hauv thermochemistry nyob heev heev ntxhuav, uas muaj lub tshav kub ntawm tsim ntawm ntau yam tshuaj los ntawm tej yam yooj yim tshuaj. Piv txwv li, thaum tshav kub kub ntawm tsim ntawm lub substance, cov mis uas CO ₂ nyob rau hauv lub gaseous lub xeev muaj ib daim duab 393,5 kJ / mol.

tswv yim tseem ceeb

Yog vim li cas yog cov ntaub ntawv tseem ceeb? Lub tshav kub ntawm tag - ib tug nqi, uas yog siv thaum lub sij hawm muab xam rau ntawm lub thermal nyhuv ntawm tej tshuaj txheej txheem. Nyob rau hauv thiaj li yuav ua xws suav yuav tsum tau siv ntawm txoj cai ntawm thermochemistry.

thermochemistry

Nws yog ib tug yuav tsum muaj kev cai lij choj uas piav txog lub zog dab cai nyob rau hauv lub chav kawm ntawm tshuaj cov tshuaj tiv thaiv. Thaum lub sij hawm sib tham cai zoo hloov nyob rau hauv lub reacting system. Ib txhia tshuaj ploj, tshiab Cheebtsam tshwm sim nyob rau hauv lawv qhov chaw. Qhov no tus txheej txheem no nrog los ntawm ib tug kev hloov nyob rau hauv lub internal zog ntawm lub cev, nws yog qhia nyob rau hauv daim ntawv ntawm cov chaw ua hauj lwm los yog thaum tshav kub kub. Lub chaw ua hauj lwm, uas yog txuam nrog rau cov extension, rau qhov tshuaj tshua yog tus nqi qis tshaj daim duab. Lub tshav kub tso tawm nyob rau hauv lub hloov dua siab tshiab ntawm ib feem mus rau lwm lub substance yuav tau ib tug zoo nqi.

Yog hais tias peb xav txog ib tug ntau yam ntawm transformations, yuav luag tag nrho cov muaj yog haum los yog kev tso tawm ntawm ib qhov nqi ntawm tshav kub. thermochemistry - ib tug tshwj xeeb seem twb tau tsim rau ib tug lus piav qhia txog qhov tshwm sim.

Hess txoj Kevcai

Vim mus rau tus thawj txoj cai ntawm thermodynamics, nws tau los ua tau mus nqa tawm muab xam rau ntawm lub thermal nyhuv nyob ntawm lub tej yam kev mob ntawm cov tshuaj cov tshuaj tiv thaiv. Raws li laij rau ntawm lub ntsiab thermochemistry txoj cai, uas yog lub cai ntawm Hess. Cia nws formulation: thermal nyhuv tshuaj transformation muaj feem xyuam rau qhov xwm, thawj zaug thiab zaum kawg lub xeev ntawm cov khoom, nws yog tsis txuam nrog txoj kev ntawm kev sis raug zoo.

Yuav ua li cas raws li nram no los ntawm qhov no formulation? Nyob rau hauv cov ntaub ntawv ntawm ib tug tej yam khoom yuav tsum tsis txhob tau mus thov tsuas mus rau ib embodiment ntawm tus sis, cov tshuaj tiv thaiv yuav tsum nqa tawm nyob rau hauv ntau txoj kev. Nyob rau hauv tej kev tshwm sim, tsis muaj teeb meem li cas koj muab cov yam khoom, lub thermal nyhuv ntawm tus txheej txheem yuav nyob twj ywm unchanged nqi. Txhais kom meej nws yog tsim nyog los saib lub ntsab lug thermal los ntawm lub intermediate transformations. Vim txoj kev cai Hess los ua tau mus nqa tawm suav ntawm tus nqi ntawm thermal los, nws yog tsis yooj yim sua mus nqa tawm nyob rau hauv lub calorimeter. Piv txwv li, rau yamntxwv lub tshav kub ntawm tsim ntawm carbon monoxide tshuaj xam los ntawm Hess txoj cai, tab sis los ntawm niaj hnub kws los mus txiav txim koj yuav tsis vam meej. Nws yog yog li ntawd ib qho tseem ceeb tshwj xeeb thermochemical ntxhuav nyob rau hauv uas lub suav qhov tseem ceeb uas muaj npe rau ntau yam tshuaj raws li sau tseg nyob rau hauv tus qauv tej yam kev mob

Ntsiab lus tseem ceeb nyob rau hauv lub xam

Muab hais tias lub tshav kub ntawm tag - yog lub tshav kub ntawm cov tshuaj tiv thaiv, ntawm kev tseem ceeb yog lub sau ua ib pawg xeev ntawm lub substance nyob rau hauv nqe lus nug. Piv txwv li, thaum noj ntsuam yog xav kom ua tau ib tug qauv lub xeev ntawm cov pa roj carbon graphite, es tsis txhob ntawm pob zeb diamond. Tsis tas li ntawd coj mus rau hauv tus account lub siab thiab qhov kub thiab txias, uas yog, qhov tej yam kev mob nyob rau hauv uas yog chiv reacting Cheebtsam. No no lub cev ntau yog tau pheev tseem ceeb cawv rau cov tshuaj tiv thaiv, yog nce los yog txo nqi ntawm lub zog. Nyob rau hauv thiaj li yuav ua yooj yim suav nyob rau hauv thermochemistry txiav txim siab los siv pob zeb ntsuas siab thiab kub.

txheem tej yam kev mob

Vim hais tias lub tshav kub ntawm tsim ntawm teeb meem - ib tug txiav txim ntawm cov nyhuv ntawm lub zog yog nyob txheem tej yam kev mob, qhov txawv lawv nyias. Kub xaiv rau lub xam ntawm 298K (25 degrees centigrade) Siab - 1 cua. Nyob rau hauv tas li ntawd, ib tug tseem ceeb point, uas yog tsim nyog hmoog los yog qhov tseeb hais tias lub tshav kub ntawm tag rau tej yam yooj yim tshuaj yog pes tsawg. Qhov no yog ib zajlus kom, vim hais tias cov yooj yim tshuaj tsis tsim lawv tus kheej, uas yog, muaj yog tsis muaj lub zog noj rau lawv tshwm sim.

ntsiab ntawm thermochemistry

Seem no niaj hnub Science News for KIDS muaj ib tug tshwj xeeb tseem ceeb, vim hais tias nws yog no nqa tawm ib qho tseem ceeb suav yog tau siv nyob rau hauv thermal hwj chim tiam. Nyob rau hauv thermochemistry, muaj ntau ntau yam lus thiab cov tswv yim uas yog ib qho tseem ceeb rau koj khiav lag luam kom tau cov kev kawm tau. Lub enthalpy (? H) ntawd hais tias ib yam tshuaj cov tshuaj tiv thaiv coj qhov chaw nyob rau hauv ib tug kaw system, muaj tsis ntxim rau cov lus teb los ntawm lwm cov reactants, lub siab yog qhov. Qhov no qhia kom meej tso cai rau koj los tham txog qhov tseeb ntawm cov lus teb ua.

Nyob ntawm seb dab tsi zoo ntawm cov tshuaj tiv thaiv yog tias, qhov ntau thiab kos npe rau ntawm lub resulting thermal nyhuv tej zaum yuav txawv ho. Yog li ntawd, rau tag nrho cov hloov uas decomposition ntawm complex tshuaj rau hauv ob peb yam yooj yim Cheebtsam, nws yog lam xav thaum tshav kub kub haum. Txuas ib tug plurality ntawm cov tshuaj tiv thaiv pib ntaub ntawv nyob rau hauv ib tug ntau yam khoom nrog qhov kev tso tawm ntawm ntau yam pauv loj nqi ntawm lub zog.

xaus

Nyob rau hauv kev daws tej teeb meem thermochemical thov tib algorithm ntawm kev ua. Ua ntej, nyob rau hauv lub rooj txiav txim rau txhua tus pib tivthaiv, zoo li cov tshuaj tiv thaiv cov khoom kom muaj nuj nqis ntawm tshav kub ntawm tag, tsis nco qab lub sau ua ib pawg xeev. Tom ntej no, armed Hess txoj cai equates los mus txiav txim tus tsis paub ntau.

Kev mloog yuav tsum tau them mus rau lub account stereochemical yam uas twb muaj lawm ua ntej thawj zaug los yog zaum kawg tshuaj nyob rau hauv ib tug kab zauv. Yog hais tias qhov tshuaj tiv thaiv yog yooj yim tshuaj, lawv txheem tshav kub ntawm tag yog sib npaug zos rau zero, i.e., tej cheebtsam muaj tsis ntxim rau cov tshwm sim tau los ntawm suav. Sim siv cov ntaub ntawv nyob rau hauv ib lub tshuaj tiv thaiv. Yog hais tias peb coj raws li ib qho piv txwv hauv tus txheej txheem ntawm tsim ntawm hlau oxide (Fe ³⁺⁾ ntshiab hlau los ntawm reacting nrog lub graphite, cov kev siv tus nqi yuav pom txheem heats ntawm tsim. Hlau oxide (Fe ³⁺⁾ nws yuav -822,1 kJ / mol rau lub graphite (yooj yim tshuaj) yog pes tsawg. Cov uas ua cov tshuaj tiv thaiv ua carbon monoxide (CO), rau cov uas qhov taw qhia muaj ib tug nqi - 110,5 kJ / mol, thaum lub tshav kub ntawm tag tso hlau sau raws nkaus Ii zero. Ntaubntawv povthawj siv standard heats ntawm tsim ntawm no tshuaj sis yog yus li nram no:

_{Hais txog} 298? H = 3 × (-110,5) - (-822,1) = -331,5 + 822,1 = 490,6 kJ.

Cais tau los ntawm kev cai lij choj Hess numeric tshwm sim, nws tseem tau mus ua ib cov zajlus kom xaus hais tias tus txheej txheem yog ib qho endothermic hloov dua siab tshiab, i.e. nws assumes zatrachivaniya zog hlau yuav txo tau cov tshuaj tiv thaiv ntawm nws ferric oxide.