Hauv txhua qhov tshuaj lom neeg, tuaj yeem tau txais cua sov los ntawm ib puag ncig lossis tso tawm rau ib puag ncig. Kev sib pauv cov cua sov ntawm cov tshuaj lom neeg thiab nws ib puag ncig yog hu ua enthalpy ntawm cov tshuaj tiv thaiv, lossis H. Txawm li cas los xij, H tsis tuaj yeem ntsuas ncaj qha - hloov pauv, cov kws tshawb fawb siv kev hloov pauv ntawm qhov kub ntawm cov tshuaj tiv thaiv nyob rau lub sijhawm kom pom qhov kev hloov pauv hauv enthalpy dhau sijhawm (sau ua H). Nrog H, tus kws tshawb fawb tuaj yeem txiav txim siab yog tias qhov tshuaj tiv thaiv ua kom sov (lossis "exothermic") lossis tau txais cua sov (lossis "endothermic"). Feem ntau, H = m x s x t, qhov twg m yog qhov hnyav ntawm cov tshuaj tiv thaiv, s yog cov cua sov tshwj xeeb ntawm cov khoom, thiab T yog qhov hloov pauv kub hauv qhov tshuaj tiv thaiv.
Kauj ruam
Txoj Kev 1 ntawm 3: Kev daws teeb meem Enthalpy
Kauj Ruam 1. Txiav txim siab qhov tshuaj tiv thaiv ntawm koj cov khoom thiab cov tshuaj tiv thaiv
Cov tshuaj tiv thaiv tshuaj twg cuam tshuam nrog ob pawg tshuaj lom neeg - cov khoom thiab cov tshuaj tiv thaiv. Cov khoom lag luam yog cov tshuaj lom neeg uas tshwm sim los ntawm cov tshuaj tiv thaiv, thaum cov tshuaj tiv thaiv yog cov tshuaj lom neeg sib xyaw lossis sib cais los tsim cov khoom lag luam. Hauv lwm lo lus, cov tshuaj tiv thaiv ntawm cov tshuaj tiv thaiv zoo li cov khoom xyaw ntawm daim ntawv qhia zaub mov, thaum cov khoom lag luam yog cov zaub mov tiav. Txhawm rau nrhiav H ntawm cov tshuaj tiv thaiv, ua ntej, txheeb xyuas cov khoom lag luam thiab cov tshuaj tiv thaiv.
Piv txwv li, hais tias peb yuav mus nrhiav enthalpy ntawm cov tshuaj tiv thaiv rau tsim cov dej los ntawm hydrogen thiab oxygen: 2H2 (Hydrogen) + O2 (Cov pa) → 2H2O (Dej). Hauv qhov kev ua zauv no, H2 thiab O2 yog tus reactant thiab H2O yog khoom.
Kauj Ruam 2. Txiav txim siab qhov hnyav ntawm cov tshuaj tiv thaiv
Tom ntej no, nrhiav qhov loj ntawm koj cov reactants. Yog tias koj tsis paub nws qhov hnyav thiab tsis tuaj yeem ntsuas nws ntawm qhov kev tshawb fawb, koj tuaj yeem siv nws cov pos hniav kom pom nws qhov hnyav tiag. Molar loj yog qhov tsis tu ncua uas tuaj yeem pom nyob hauv cov lus niaj zaus (rau cov ntsiab lus ib leeg) thiab lwm yam khoom siv tshuaj (rau cov lwg me me thiab cov sib txuas). Tsuas yog muab cov molar loj ntawm txhua cov tshuaj tiv thaiv los ntawm tus naj npawb ntawm moles los nrhiav qhov hnyav ntawm cov tshuaj tiv thaiv.
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Hauv cov piv txwv dej, peb cov tshuaj tiv thaiv kab mob yog hydrogen thiab cov pa oxygen, uas muaj cov pos hniav loj ntawm 2 g thiab 32 g. Txij li thaum peb siv 2 moles ntawm hydrogen (txiav txim los ntawm qhov sib npaug ntawm 2 hauv H2) thiab 1 mole ntawm cov pa oxygen (txiav txim siab los ntawm qhov tsis muaj qhov sib txuam hauv O2), peb tuaj yeem suav tag nrho qhov hnyav ntawm cov tshuaj tiv thaiv raws li hauv qab no:
2 × (2g) + 1 × (32g) = 4g + 32g = 36g ua
Kauj Ruam 3. Nrhiav cov cua sov tshwj xeeb ntawm koj cov khoom
Tom ntej, nrhiav qhov tshwj xeeb cua sov ntawm cov khoom koj tab tom tshuaj xyuas. Txhua lub hauv paus lossis txheej txheem muaj qhov tshwj xeeb cov cua sov tshwj xeeb: tus nqi no yog qhov tsis tu ncua thiab feem ntau pom nyob hauv cov khoom siv tshuaj lom neeg (piv txwv li, hauv lub rooj tom qab ntawm phau ntawv tshuaj lom neeg). Muaj ntau txoj hauv kev los xam cov cua sov tshwj xeeb, tab sis rau cov qauv peb siv, peb siv chav Joule/gram ° C.
- Nco ntsoov tias yog tias koj cov kab zauv muaj ntau yam khoom lag luam, koj yuav tsum tau suav qhov enthalpy rau cov tshuaj tiv thaiv ntawm cov khoom siv los tsim txhua yam khoom, tom qab ntawd ntxiv lawv txhawm rau nrhiav tag nrho enthalpy rau cov tshuaj tiv thaiv.
- Hauv peb qhov piv txwv, cov khoom kawg yog dej, uas muaj cov cua sov tshwj xeeb ntawm kwv yees li. 4.2 joules/gram ° C..
Kauj Ruam 4. Nrhiav qhov sib txawv ntawm qhov kub tom qab qhov tshwm sim tshwm sim
Tom ntej no, peb yuav pom T, qhov hloov pauv ntawm qhov kub thiab txias ua ntej thiab tom qab cov tshuaj tiv thaiv. Rho tawm qhov pib qhov kub ntawm qhov tshuaj tiv thaiv (lossis T1) los ntawm qhov kub kawg tom qab qhov tshuaj tiv thaiv (lossis T2) los xam nws. Raws li hauv kev ua haujlwm tshuaj feem ntau, Kelvin (K) ntsuas kub tau siv (txawm hais tias Celsius (C) yuav muab qhov txiaj ntsig zoo ib yam).
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Rau peb tus piv txwv, cia peb hais qhov pib ntsuas kub ntawm qhov tshuaj tiv thaiv yog 185K tab sis txias mus rau 95K thaum qhov tshuaj tiv thaiv tiav. Hauv qhov teeb meem no, T yog xam raws li hauv qab no:
T = T2 - T1 = 95K - 185K = - 90K ib
Kauj Ruam 5. Siv cov mis H = m x s x T los daws
Yog tias koj muaj m, qhov hnyav ntawm cov tshuaj tiv thaiv, s, cov cua sov tshwj xeeb ntawm cov khoom, thiab T, kev hloov pauv ntawm qhov kub ntawm cov tshuaj tiv thaiv, tom qab ntawd koj tau npaj los nrhiav cov enthalpy ntawm cov tshuaj tiv thaiv. Ntsuas koj qhov txiaj ntsig rau hauv cov mis H = m x s x T thiab muab sib ntxiv los daws. Koj cov lus teb tau sau rau hauv chav zog, uas yog Joules (J).
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Rau peb qhov teeb meem piv txwv, enthalpy ntawm cov tshuaj tiv thaiv yog:
H = (36g) × (4.2 JK-1 g-1) × (-90K) = - 13,608J
Kauj Ruam 6. Txiav txim siab seb koj qhov tshuaj tiv thaiv tau txais lossis poob zog
Ib qho ntawm qhov laj thawj feem ntau rau kev suav H rau ntau yam kev cuam tshuam yog txiav txim siab yog tias qhov tshuaj tiv thaiv yog exothermic (poob lub zog thiab tso tawm cua sov) lossis endothermic (nce lub zog thiab nqus cua sov). Yog tias kos npe ntawm koj cov lus teb kawg rau H yog qhov zoo, tom qab ntawd cov tshuaj tiv thaiv yog endothermic. Lub caij no, yog tias qhov kos npe tsis zoo, cov tshuaj tiv thaiv yog exothermic. Qhov loj dua tus lej, qhov ntau dua qhov exo- lossis endothermic cov tshuaj tiv thaiv. Ceev faj nrog cov tshuaj tiv thaiv exothermic - lawv qee zaum tso ntau lub zog, uas, yog tias tso tawm sai, tuaj yeem ua rau tawg.
Hauv peb qhov piv txwv, cov lus teb kawg yog -13608J. Txij li qhov kos npe tsis zoo, peb paub tias peb cov tshuaj tiv thaiv yog exothermic. Qhov no ua rau kev nkag siab - H.2 thiab O2 yog gas, hos H.2O, cov khoom, yog kua. Cov pa kub (hauv daim ntawv ntawm cov pa) yuav tsum tso lub zog mus rau ib puag ncig hauv daim ntawv ua cua sov, kom txias nws los ua kua, uas yog, cov tshuaj tiv thaiv rau H2O yog exothermic.
Txoj Kev 2 ntawm 3: Kwv yees Qhov Loj Enthalpy
Kauj Ruam 1. Siv lub zog sib zog los kwv yees tus enthalpy
Yuav luag txhua qhov tshuaj lom neeg cuam tshuam nrog kev tsim lossis tawg ntawm kev sib txuas ntawm cov atoms. Txij li thaum tshuaj lom neeg lub zog, lub zog tsis tuaj yeem rhuav tshem lossis tsim tau, yog tias peb paub ntau npaum li cas lub zog xav tau los tsim lossis rhuav tshem cov nyiaj hauv cov tshuaj tiv thaiv, peb tuaj yeem kwv yees kev hloov pauv ntawm enthalpy rau tag nrho cov tshuaj tiv thaiv nrog qib siab ntawm qhov raug los ntawm kev ntxiv cov nyiaj no lub zog.
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Piv txwv li, qhov tshuaj tiv thaiv siv H2 + F2 H 2 HF. Hauv qhov sib npaug no, lub zog xav tau txhawm rau txhawm rau rhuav tshem H atoms hauv H molecule yog2 yog 436 kJ/mol, thaum lub zog xav tau rau F.2 yog 158 kJ/mol Thaum kawg, lub zog xav tau los ua HF los ntawm H thiab F yog = -568 kJ/mol. Peb suav nrog 2 vim tias cov khoom hauv kab zauv yog 2 HF, yog li 2 × -568 = -1136 kJ/mol. Ntxiv lawv txhua tus ua ke, peb tau txais:
436 + 158 + -1136 = - 542 kJ/mol.
Kauj Ruam 2. Siv enthalpy ntawm kev tsim los kwv yees cov enthalpy
Enthalpy ntawm kev tsim yog txheej txheej H uas sawv cev rau kev hloov pauv enthalpy ntawm cov tshuaj tiv thaiv los tsim cov tshuaj lom neeg. Yog tias koj paub cov enthalpy ntawm kev tsim kom tsim cov khoom lag luam thiab cov tshuaj tiv thaiv kab mob hauv qhov sib npaug, koj tuaj yeem ntxiv lawv los kwv yees cov enthalpy zoo li lub zog cog lus tau piav qhia saum toj no.
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Piv txwv li, qhov sib npaug siv C.2H5OH + 3O2 → 2 COJ2 + 3 hli2O. Hauv kab zauv no, peb paub tias enthalpy ntawm kev tsim rau cov tshuaj tiv thaiv hauv qab no yog:
C2H5OH → 2C + 3H2 +0.5 hli2 = 228 kJ/mol
2C + 2O Nws2 → 2 COJ2 = -394 × 2 = -788 kJ/mol
3H2 +1.5 Nws2 → 3 H os2O = -286 × 3 = -858 kJ/mol
Txij li peb tuaj yeem suav cov lej no kom tau txais C.2H5OH + 3O2 → 2 COJ2 + 3 hli2O, los ntawm cov tshuaj tiv thaiv peb tab tom nrhiav kom pom enthalpy, peb tsuas yog xav tau ntxiv cov enthalpy ntawm cov tshuaj tiv thaiv ntawm kev tsim los saum toj no kom pom cov enthalpy ntawm cov tshuaj tiv thaiv no, raws li hauv qab no:
228 + -788 + -858 = - 1418 kJ/mol.
Kauj Ruam 3. Tsis txhob hnov qab hloov daim paib thaum thim rov qab qhov sib npaug
Nws yog ib qho tseem ceeb kom nco ntsoov tias thaum koj siv enthalpy ntawm kev tsim los laij cov enthalpy ntawm cov tshuaj tiv thaiv, koj yuav tsum hloov pauv qhov kos npe ntawm enthalpy ntawm kev tsim thaum twg koj thim qhov sib npaug rau cov tshuaj tiv thaiv ntawm cov ntsiab lus. Hauv lwm lo lus, yog tias koj thim ib lossis ntau qhov ntawm koj qhov sib npaug rau kev tsim cov tshuaj tiv thaiv kom cov khoom lag luam thiab cov tshuaj tiv thaiv thim rov qab ib leeg tawm, hloov cov cim ntawm enthalpy ntawm kev tsim cov tshuaj tiv thaiv uas koj tab tom pauv.
Hauv qhov piv txwv saum toj no, nco ntsoov tias kev tsim cov tshuaj tiv thaiv peb siv rau C.2H5OH upside down. C2H5OH → 2C + 3H2 +0.5 hli2 qhia C.2H5OH raug faib, tsis tsim. Txij li thaum peb thim rov qab qhov sib npaug no kom cov khoom lag luam thiab cov tshuaj tiv thaiv thim rov qab ib leeg tawm, peb hloov pauv qhov cim ntawm enthalpy ntawm kev tsim los muab 228 kJ/mol. Qhov tseeb, enthalpy ntawm kev tsim rau C.2H5OH yog -228 kJ/mol
Txoj Kev 3 ntawm 3: Soj Ntsuam Kev Hloov Kho Enthalpy hauv Kev sim
Kauj Ruam 1. Nqa lub khob huv huv thiab sau nws nrog dej
Nws yog qhov yooj yim kom pom lub hauv paus ntsiab lus ntawm enthalpy nrog kev sim yooj yim. Txhawm rau kom ntseeg tau tias koj qhov kev sim tshuaj tiv thaiv tsis kis nrog cov tshuaj sab nraud, ntxuav thiab ua kom tsis huv lub ntim uas koj npaj yuav siv. Cov kws tshawb fawb siv cov ntim ntim tshwj xeeb hu ua calorimeters txhawm rau ntsuas enthalpy, tab sis koj tuaj yeem tau txais txiaj ntsig zoo nrog rau iav lossis raj me me. Txhua lub thawv twg koj siv, sau nws nrog dej huv, chav sov. Koj yuav tsum tau sim hauv chav nrog txias txias.
Rau qhov kev sim no, koj yuav xav tau lub thawv me me haum. Peb yuav tshuaj xyuas qhov cuam tshuam ntawm kev hloov pauv ntawm Alka-Seltzer rau hauv dej, yog li cov dej koj siv tsawg dua, qhov tshaj tawm qhov ntsuas kub yuav hloov pauv
Kauj Ruam 2. Ntxig tus pas ntsuas kub rau hauv lub khob
Siv tus pas ntsuas kub thiab muab tso rau hauv lub khob kom lub taub ntsuas kub nyob hauv qab dej. Nyeem qhov kub ntawm cov dej - rau peb lub hom phiaj, qhov kub ntawm cov dej tau qhia los ntawm T1, thawj qhov kub ntawm qhov tshwm sim.
Cia peb hais tias peb ntsuas qhov ntsuas dej thiab qhov tshwm sim yog 10 degrees C. Hauv ob peb kauj ruam, peb yuav siv cov ntsuas kub no los ua pov thawj txoj cai enthalpy
Kauj Ruam 3. Ntxiv ib Alka-Seltzer rau hauv lub khob
Thaum koj npaj txhij pib qhov kev sim, tso Alka-Seltzer rau hauv dej. Koj yuav pom tam sim ntawd cov nplej tau ua npuas thiab khaus. Thaum cov hlaws yaj yaj hauv dej, lawv tawg mus ua tshuaj bicarbonate (HCO.)3-) thiab citric acid (uas cuam tshuam rau hauv daim ntawv ntawm hydrogen ions, H.+). Cov tshuaj no ua rau dej thiab cov pa roj carbon dioxide hauv qhov sib npaug 3HCO3− + 3 hli+ → 3 H os2O + 3CO2.
Kauj Ruam 4. Ntsuas qhov ntsuas kub thaum qhov tshuaj tiv thaiv tiav
Saib raws li cov tshuaj tiv thaiv ua tiav - Alka -Seltzer granules yuav maj mam yaj. Sai li cov tshuaj tiv thaiv cov qoob loo xaus (lossis tau qeeb), ntsuas qhov kub dua. Cov dej yuav tsum txias dua ua ntej. Yog tias nws sov dua, qhov kev sim tuaj yeem cuam tshuam los ntawm kev tawm sab nraud (piv txwv li, yog tias chav koj nyob sov sov).
Rau peb qhov kev sim piv txwv, peb hais tias qhov kub ntawm cov dej yog 8 degrees C tom qab cov nplej tsis khov
Kauj Ruam 5. Kwv yees enthalpy ntawm cov tshuaj tiv thaiv
Hauv qhov kev sim ua zoo tshaj plaws, thaum koj tso Alka-Seltzer lis dej rau hauv dej, nws tsim cov dej thiab cov pa roj carbon dioxide (cov pa tuaj yeem pom raws li ua npuas ncauj) thiab ua rau qhov kub ntawm cov dej poob. Los ntawm cov ntaub ntawv no, peb kwv yees cov tshuaj tiv thaiv yog endothermic - uas yog, nws nqus lub zog los ntawm ib puag ncig ib puag ncig. Cov tshuaj yaj dej ua kom yaj tau xav tau lub zog ntxiv los tsim cov khoom siv roj cua, yog li lawv nqus tau lub zog nyob hauv daim ntawv cua sov los ntawm ib puag ncig (hauv qhov kev sim no, dej). Qhov no ua rau dej kub poob.
