Cov Lus Nug Piv Txwv Sib Tham Txog Kev Hloov Pauv Enthalpy Hauv Cov Xwm Txheej Txheem
Pendahuluuan
Kev hloov pauv Enthalpy yog lub tswv yim tseem ceeb hauv thermochemistry uas ua lub luag haujlwm tseem ceeb hauv ntau yam txheej txheem tshuaj lom neeg. Hauv tsab xov xwm no, peb yuav tham txog ntau yam yuav ua li cas xam thiab nkag siab txog kev hloov pauv enthalpy nyob rau hauv cov xwm txheej txheem los ntawm ntau qhov piv txwv teeb meem thiab kev sib tham dav dav. Tsab xov xwm no yuav pab tau rau cov tub ntxhais kawm, cov tub ntxhais kawm qib siab, thiab txhua tus neeg uas kawm chemistry kom nkag siab zoo dua txog cov ncauj lus no.
Nkag Siab Txog Enthalpy Thiab Nws Cov Kev Hloov Pauv
Enthalpy (H) yog tag nrho lub zog ntawm ib lub cev, uas muaj lub zog sab hauv thiab lub zog cuam tshuam nrog lub siab thiab ntim. Hauv cov tshuaj lom neeg, peb feem ntau xav paub txog qhov kev hloov pauv enthalpy (ΔH), uas qhia txog tag nrho lub zog hloov pauv thaum lub sijhawm tshuaj tiv thaiv ntawm qhov siab tas li.
Qhov kev hloov pauv enthalpy nyob rau hauv cov xwm txheej txheem (ΔH⁰) yog qhov kev hloov pauv enthalpy thaum txhua yam reactants thiab cov khoom nyob hauv lawv cov xeev txheem, uas yog, ntawm qhov siab ntawm 1 atm thiab qhov kub feem ntau yog 25 ° C (298 K).
Cov Lus Nug Piv Txwv thiab Kev Sib Tham
Lo Lus Nug 1: Kev Kub Hnyiab Methane
Lus Nug: Xam qhov kev hloov pauv enthalpy txheem (ΔH⁰) rau qhov combustion ntawm 1 mole ntawm methane (\(CH_4\)) raws li cov qauv hauv qab no:
\[ CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l) \]
Nws paub tias:
– ΔH⁰f \(CH_4(g)\) = -74.8 kJ/mol
– ΔH⁰f \(CO_2(g)\) = -393.5 kJ/mol
– ΔH⁰f \(H_2O(l)\) = -285.8 kJ/mol
Kev Sib Tham:
Qhov kev hloov pauv enthalpy txheem rau kev tshuaj lom neeg tuaj yeem suav nrog siv Hess txoj cai los ntawm cov qauv hauv qab no:
\[ \Delta H⁰ = ∑ ΔH⁰f(khoom) – ∑ ΔH⁰f(reactant) \]
Ua ntej, txheeb xyuas tus qauv enthalpy ntawm kev tsim rau txhua yam khoom hauv cov tshuaj tiv thaiv:
– \( ΔH⁰f_{CH_4(g)} = -74.8 \) kJ/mol
– \( ΔH⁰f_{CO_2(g)} = -393.5 kJ/mol
– \( ΔH⁰f_{H_2O(l)} = -285.8 \) kJ/mol (×2 rau ob moles \(H_2O\))
Tom qab ntawd, xam qhov sib npaug ntawm cov enthalpies ntawm kev tsim cov khoom thiab reactants:
\[ ∑ ΔH⁰f(khoom) = [-393.5] + [2(-285.8)]
= -393.5 + (-571.6)
= -965.1 kJ/mol
\[ ∑ ΔH⁰f(reactant) = [-74.8] + [0] \]
(Txhua yam khoom sib xyaw ua ke hauv lawv daim ntawv yooj yim muaj tus qauv enthalpy ntawm kev tsim ntawm 0 kJ / mol)
Tom qab ntawd, xam qhov kev hloov pauv enthalpy txheem (ΔH⁰):
\[ ΔH⁰ = -965.1 – (-74.8)
= -965.1 + 74.8
= -890.3 kJ/mol
Yog li, qhov kev hloov pauv enthalpy txheem rau qhov combustion ntawm 1 mole ntawm methane yog -890.3 kJ / mol.
Lo Lus Nug 2: Kev Ua Dej Tshwm Sim
Lus Nug: Xam qhov kev hloov pauv enthalpy txheem (ΔH⁰) rau kev tsim dej los ntawm hydrogen thiab oxygen raws li cov qauv hauv qab no:
\[ 2H_2(g) + O_2(g) \rightarrow 2H_2O(l) \]
Nws paub tias:
– ΔH⁰f \(H_2O(l)\) = -285.8 kJ/mol
Kev Sib Tham:
Peb yuav tsum nrhiav qhov kev hloov pauv ntawm tus qauv enthalpy rau qhov kev tshuaj tiv thaiv los ntawm cov tshuaj pib mus rau cov khoom xav tau. Siv tus qauv enthalpy ntawm kev tsim:
\[ ΔH⁰ = ∑ ΔH⁰f(khoom) – ∑ ΔH⁰f(reactant) \]
Xam qhov enthalpy ntawm kev tsim cov khoom thiab cov reactants:
\[
\begin{aligned}
∑ ΔH⁰f(khoom) & = [2(-285.8)] \\
∑ ΔH⁰f(khoom) & = -571.6 kJ/mol
\end{aligned}
\]
\[
ΔH⁰f(H_2(g)) = 0 kJ/mol
ΔH⁰f(O_2(g)) = 0 kJ/mol
∑ ΔH⁰f(cov tshuaj tiv thaiv) = [2(0)] + [0] = 0 kJ/mol}
\]
Tom qab ntawd, xam qhov kev hloov pauv enthalpy txheem (ΔH⁰):
\[ ΔH⁰ = -571.6 kJ/mol} \]
Yog li, qhov kev hloov pauv enthalpy txheem rau kev tsim dej yog -571.6 kJ / mol.
Lo Lus Nug 3: Kev lwj ntawm Nitrogen Dioxide
Lus Nug: Xam qhov kev hloov pauv enthalpy txheem (ΔH⁰) rau kev rhuav tshem cov nitrogen dioxide (NO_2) mus rau hauv cov pa roj nitrogen monoxide (NO_2) thiab cov pa oxygen (O₂) raws li cov qauv hauv qab no:
\[ 2NO_2(g) \rightarrow 2NO(g) + O_2(g) \]
Nws paub tias:
– ΔH⁰f \(NO_2(g)\) = 33.2 kJ/mol
– ΔH⁰f \(NO(g)\) = 90.3 kJ/mol
Kev Sib Tham:
Kev xam lej zoo sib xws:
\[ ΔH⁰ = ∑ ΔH⁰f(khoom) – ∑ ΔH⁰f(reactant) \]
Xam qhov enthalpy ntawm kev tsim ntawm cov khoom:
\[
\begin{aligned}
∑ ΔH⁰f(khoom) & = [2( ΔH⁰f_{NO(g)} )] + [ ΔH⁰f_{O_2(g)}] \\
& = [2(90.3)] + [0] \\
& = 180.6 kJ/mol
\end{aligned}
\]
Xam qhov enthalpy ntawm kev tsim ntawm cov reactants:
\[
\begin{aligned}
∑ ΔH⁰f(reactant) & = [2( ΔH⁰f_{NO_2(g)} )] \\
& = [2(33.2)] \\
& = 66.4 kJ/mol
\end{aligned}
\]
Xam qhov kev hloov pauv enthalpy txheem (ΔH⁰):
\[ ΔH⁰ = 180.6 – 66.4 = 114.2 kJ/mol} \]
Yog li, qhov kev hloov pauv enthalpy txheem rau kev rhuav tshem ntawm nitrogen dioxide yog 114.2 kJ / mol.
Xaus
Kev suav cov kev hloov pauv enthalpy tus qauv (ΔH⁰) yog ib qho txheej txheem tseem ceeb hauv thermochemistry. Los ntawm kev nkag siab txog yuav ua li cas siv cov qauv enthalpies ntawm kev tsim thiab siv Hess txoj cai, peb tuaj yeem txiav txim siab qhov kev hloov pauv zog hauv ntau yam tshuaj lom neeg. Los ntawm cov piv txwv teeb meem saum toj no, cov nyeem ntawv yuav tsum tau txais kev nkag siab thiab lub peev xwm los xam cov kev hloov pauv enthalpy rau ntau yam tshuaj lom neeg. Kev paub no tseem ceeb tsis yog rau kev kawm xwb tab sis kuj rau ntau yam kev siv hauv kev lag luam thiab kev tshawb fawb.
