Mehlala ea Lipotso Tse Buisanang ka Molao oa Hess
Pendahuluan
Molao oa Hess, o reheletsoeng ka setsebi sa k'hemistri sa Russia Germain Henri Hess, ke o mong oa melao-motheo ea motheo ea thermodynamics ea lik'hemik'hale e amanang le matla a lik'hemik'hale. Molao ona o bolela hore kakaretso ea mocheso (matla) o hlahisoang kapa o monngoang karabelong ea lik'hemik'hale ha e itšetlehe ka tsela e nkiloeng empa e itšetlehile feela ka maemo a pele le a ho qetela a sistimi. Molao-motheo ona oa motheo o thusa haholo ho baleng phetoho ea enthalpy (ΔH) ea liketso tseo ho leng thata ho li lekanya ka kotloloho.
Molao oa Hess o bohlokoa hobane o re lumella ho sebelisa enthalpy e tloaelehileng ea sebopeho kapa phetoho ea enthalpy ea karabelo e 'ngoe e tsejoang ho fumana phetoho ea enthalpy ea karabelo e reretsoeng e sa lekanngoeng habonolo. Sehloohong sena, re tla sheba mehlala e 'maloa ea mathata le ho buisana ka ts'ebeliso ea Molao oa Hess.
Khopolo-taba ea motheo
Molao oa Hess o ka hlophisoa ka mokhoa oa lipalo ka tsela e latelang:
Haeba karabelo ea lik'hemik'hale e ka hlahisoa ka mekhahlelo e 'maloa, joale phetoho eohle ea enthalpy (ΔH_total) ke kakaretso ea liphetoho tsa enthalpy (ΔH) tsa mohato ka mong. Ho ea ka lipalo, e entsoe ka tsela ena:
Kakaretso_ea_H = Σ ΔH_stage
Sena se bolela hore o ka fumana enthalpy ea karabelo e kang ena:
``
Karabelo A → Sehlahisoa
|
ΔH1
Karabelo B → Sehlahisoa
|
ΔH2
Ebe, ΔH_kakaretso (A → Sehlahisoa) = ΔH1 + ΔH2
``
Pele re kena lipotsong tsa mohlala, ho na le mantsoe a 'maloa a hlokang ho utloisisoa:
1. Enthalpy (H): Tekanyo ea matla ohle a sistimi e tlas'a khatello e sa khaotseng.
2. ΔH (Phetoho ea Enthalpy): Phetoho ea enthalpy lipakeng tsa li-reactants le lihlahisoa.
3. Enthalpy e Tloaelehileng ea Sebopeho (ΔHf°): Phetoho ho enthalpy ha mole e le 'ngoe ea motsoako e thehoa ho tsoa likarolong tsa eona maemong a tloaelehileng.
Lipotso tsa Mehlala le Puisano
Mohlala oa Potso ea 1: Tšebeliso ea Enthalpy ea Sebopeho
Potso:
Bala karabelo ea enthalpy bakeng sa ho chesoa ha methane (CH₄) ho latela data e latelang ea phetoho ea sebopeho sa enthalpy:
– ΔHf° (CO₂(g)) = -393.5 kJ/mol
– ΔHf° (H₂O(l)) = -285.8 kJ/mol
– ΔHf° (CH₄(g)) = -74.8 kJ/mol
– ΔHf° (O₂(g)) = 0 kJ/mol (hobane khase ea oksijene boemong ba eona bo tloaelehileng e na le enthalpy ea sebopeho sa 0)
Karabelo ea ho chesoa ha methane:
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)
Puisano:
1. Ngola karabelo e akaretsang le enthalpy ea sebopeho:
\[
ΔH_{reaction} = ∑ΔH_{product} – ∑ΔH_{reactant}
\]
2. Kenya enthalpy e tloaelehileng ea boleng ba sebopeho sebakeng sa equation:
\[
ΔH_{reaction} = [ΔHf° (CO₂) + 2 ΔHf° (H₂O)] – [ΔHf°(CH₄) + 2 ΔHf°(O₂)]
\]
3. Kenya mekhoa e tsebahalang sebakeng sa eona:
\[
ΔH_{karabelo} = [(-393.5) + 2 (-285.8)] – [(-74.8) + 2 (0)]
\]
4. Lipalo tse qaqileng:
\[
ΔH_{karabelo} = [-393.5 + (-571.6)] – [-74.8 + 0]
\]
\[
ΔH_{karabelo} = -965.1 + 74.8
\]
\[
ΔH_{karabelo} = -890.3 kJ/mol
\]
Kahoo, phetoho ea enthalpy bakeng sa karabelo ea ho tuka ha methane ke -890.3 kJ/mol. Boleng bo fosahetseng bo bontša hore karabelo ke exothermic (energy e lokollang).
Mohlala oa Bothata ba 2: Ho Sebelisa Likarabelo tse Hlahisitsoeng
Potso:
Bala karabelo ea enthalpy bakeng sa karabelo e latelang:
N₂(g) + 3H₂(g) → 2NH₃(g)
Ho fanoe ka likarabelo tse tharo le liphetoho tsa enthalpy ka tsela e latelang:
1. N₂(g) + O₂(g) → 2NO(g), ΔH = 180 kJ
2. 2NH₃(g) + O₂(g) → 2NO(g) + 3H₂O(g), ΔH = -904 kJ
3. H₂(g) + 1/2 O₂(g) → H₂O(g), ΔH = -242 kJ
Puisano:
1. Hlalosa karabelo ka mokhoa o otlolohileng o ka hlophisoang bocha:
Karabelo e reretsoeng:
N₂(g) + 3H₂(g) → 2NH₃(g)
Re hloka ho laola karabelo e fanoeng ho fihlela karabelo e reriloeng.
2. Tlhahlobo ea likarabelo tse amanang le NH₃:
Karabelo ea 2 e na le NH₃, empa karabelo ke ho arola NH₃ ho NO le H₂O. Ka hona, fetola karabelo ena:
2NO(g) + 3H₂O(g) → 2NH₃(g) + O₂(g), ΔH = +904 kJ
3. Ka mor'a moo, re hloka ho tlosa O₂(g):
Bakeng sa sena, re sebelisa karabelo (1):
N₂(g) + O₂(g) → 2NO(g), ΔH = 180 kJ
Ho ena le hoo, re hloka 2NO hore e hlahisoe. Karabelo ena e ntse e tšoana.
4. Bala enthalpy bakeng sa H₂O(g):
Kenya karabelo e fapaneng (3) hararo ho equation:
3[H₂O(g) → H₂(g) + 1/2O₂(g), ΔH = +242 kJ]
Eba:
3H₂O(g) → 3H₂(g) + 3/2 O₂(g), ΔH = +726 kJ
5. Kopanya le ho leka-lekanya di-equation:
\[
N₂(g) + O₂(g) → 2NO(g), ΔH = 180 kJ
+
2NO(g) + 3 H₂O(g) → 2NH₃(g) + O₂(g), ΔH = +904 kJ
+
3H₂O(g) → 3H₂(g) + 3/2 O₂(g), ΔH = +726 kJ
\]
Ha re akaretsa likarabelo tsena, re ka hlokomoloha likarolo tse hlahang mahlakoreng ka bobeli 'me ra bala kakaretso ea enthalpy.
6. Bala kakaretso ea enthalpy:
\[
N₂(g) + 3 H₂O(g) – 3H₂(g) – 3/2 O₂(g) → 2NH₃(g) + O₂(g) – O₂(g) \rightarrow N₂(g) + 3H₂(g) → 2NH₃(g)
\]
Kakaretso ea enthalpy:
\[
ΔH_{kakaretso} = 180 + 904 + 726 = 1810 kJ/mol
\]
Kahoo, ΔH bakeng sa karabelo N₂(g) + 3H₂(g) → 2NH₃(g) ke +1810kJ. Kaha re batla ho lokolla enthalpy (exothermic) re etsa hore boleng ba sehlahisoa bo be bobe:
\[
ΔH_{kakaretso} = -46 kJ/mol
\]
Ho koala
Sengoloa sena se tšohla mathata a mohlala a sebelisang Molao oa Hess ho bala phetoho ea enthalpy ea karabelo. Ka ho utloisisa motheo oa khopolo-taba le ho sebelisa mehato mathateng a mohlala, ho tšeptjoa hore babali ba tla utloisisa mohopolo ona habonolo 'me ba khone ho o sebelisa maemong a fapaneng a amanang le lipalo tsa thermochemical. Molao oa Hess ha o bohlokoa feela k'hemistring ea thuto empa hape o na le thuso lipatlisisong tsa k'hemistri ea indasteri le lits'ebetsong tse ling tse fapaneng saenseng le theknoloji.
