Mienzaniso yeMibvunzo yeKukurukura Mutemo waHess
Pendauluan
Mutemo waHess, wakatumidzwa zita remunyanzvi wemakemikari wekuRussia Germain Henri Hess, ndeimwe yenheyo huru dzemakemikari ethermodynamics ane chekuita nesimba remakemikari. Mutemo uyu unoti huwandu hwese hwekupisa (simba) hunogadzirwa kana kunyudzwa mumakemikari hahutsamiri panzira inotorwa asi chete pamamiriro ekutanga uye ekupedzisira ehurongwa. Iyi nheyo huru inobatsira zvikuru pakuverenga shanduko ye enthalpy (ΔH) yemaitiro akaoma kuyera zvakananga.
Mutemo waHess wakakosha nekuti unotibvumira kushandisa enthalpy yakajairwa yekuumbwa kana shanduko ye enthalpy yeimwe reaction inozivikanwa kuti tiwane shanduko ye enthalpy ye reaction yakatarwa isingayereki nyore. Muchinyorwa chino, tichatarisa mienzaniso yakati wandei yematambudziko uye tichakurukura mashandisirwo eMutemo waHess.
Dzidziso huru
Mutemo waHess unogona kuumbwa nenzira yemasvomhu seizvi:
Kana maitiro emakemikari achigona kuratidzwa muzvikamu zvakasiyana-siyana, saka shanduko yese ye enthalpy (ΔH_total) ndiyo huwandu hweshanduko dze enthalpy (ΔH) dzechikamu chimwe nechimwe. Pamasvomhu, inogadzirwa seizvi:
ΔH_total = Σ ΔH_stage
Izvi zvinoreva kuti unogona kuwana enthalpy yemhinduro yakaita seiyi:
``
Mhinduro A → Chigadzirwa
|
ΔH1
Mhinduro B → Chigadzirwa
|
ΔH2
Zvadaro, ΔH_huwandu (A → Chigadzirwa) = ΔH1 + ΔH2
``
Tisati tapinda mumibvunzo yemuenzaniso, pane mazwi akati wandei anofanira kunzwisiswa:
1. Enthalpy (H): Chiyero chesimba rose rehurongwa huri pasi pekumanikidzwa nguva dzose.
2. ΔH (Kuchinja kweEnthalpy): Kuchinja kwe enthalpy pakati pe reactants nezvigadzirwa.
3. Standard Enthalpy yeKuumbwa (ΔHf°): Kuchinja kwe enthalpy kana mole imwe yekombuta ikaumbwa kubva muzvinhu zvayo mumamiriro akajairwa.
Mibvunzo yemuenzaniso nekukurukurirana
Muenzaniso Mubvunzo 1: Kushandiswa kweEnthalpy yeKuumbwa
Mubvunzo:
Verenga reaction enthalpy yekupiswa kwemethane (CH₄) zvichibva pane data rinotevera rekuchinja kwe enthalpy pakuumbwa:
– 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 (nekuti gasi reokisijeni riri mumamiriro aro akajairika rine enthalpy yekuumbwa kwe0)
Kuita kwekupisa kweMethane:
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)
Kukurukurirana:
1. Nyora maitiro akajairika uye enthalpy yekuumbwa:
\[
ΔH_{reaction} = ∑ΔH_{product} – ∑ΔH_{reactant}
\]
2. Isa enthalpy yakajairika yemaitiro ekuumbwa mu equation:
\[
ΔH_{reaction} = [ΔHf° (CO₂) + 2 ΔHf° (H₂O)] – [ΔHf°(CH₄) + 2 ΔHf°(O₂)]
\]
3. Tsiva tsika dzinozivikanwa:
\[
ΔH_{reaction} = [(-393.5) + 2 (-285.8)] – [(-74.8) + 2 (0)]
\]
4. Kuverenga kwakadzama:
\[
ΔH_{reaction} = [-393.5 + (-571.6)] – [-74.8 + 0]
\]
\[
ΔH_{reaction} = -965.1 + 74.8
\]
\[
ΔH_{reaction} = -890.3 kJ/mol
\]
Saka, shanduko ye enthalpy ye combustion reaction ye methane i -890.3 kJ/mol. Nhamba isina kunaka inoratidza kuti reaction yacho i exothermic (releasing energy).
Muenzaniso Dambudziko rechipiri: Kushandisa Maitiro Akabva
Mubvunzo:
Verenga reaction enthalpy ye reaction inotevera:
N₂(g) + 3H₂(g) → 2NH₃(g)
Zvichienderana nemhinduro nhatu uye shanduko dze enthalpy, zvinotevera:
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
Kukurukurirana:
1. Tsanangura maitiro acho nenzira yakatsetseka inogona kurongwazve:
Maitiro echinangwa:
N₂(g) + 3H₂(g) → 2NH₃(g)
Tinofanira kuchinja maitiro akapihwa kuti tisangane nemaitiro acho.
2. Kuongororwa kwemaitiro ane chekuita neNH₃:
Reaction 2 ine NH₃, asi reaction ndeyekuparadzanisa NH₃ kuita NO uye H₂O. Saka, chinja reaction iyi:
2NO(g) + 3H₂O(g) → 2NH₃(g) + O₂(g), ΔH = +904 kJ
3. Tevere, tinofanira kubvisa O₂(g):
Pakuita izvi, tinoshandisa reaction (1):
N₂(g) + O₂(g) → 2NO(g), ΔH = 180 kJ
Pane kudaro, tinoda 2NO kuti ibudiswe. Maitiro aya anoramba akafanana.
4. Verenga enthalpy yeH₂O(g):
Wedzera reverse reaction (3) katatu mu equation:
3[H₂O(g) → H₂(g) + 1/2O₂(g), ΔH = +242 kJ]
Iva:
3H₂O(g) → 3H₂(g) + 3/2 O₂(g), ΔH = +726 kJ
5. Sanganisa uye enzanisa maequation:
\[
N₂(g) + O₂(g) → 2NO(g), ΔH = 180 kJ
+
2NO(g) + 3 H₂O(g) → 2NH₃(g) + O₂(g), ΔH = +904 kJ
+
3H₂O(g) → 3H₂(g) + 3/2 O₂(g), ΔH = +726 kJ
\]
Pakupfupisa maitiro aya, tinogona kufuratira zvikamu zvinoonekwa kumativi ese uye kuverenga huwandu hwese hwe enthalpy.
6. Verenga huwandu hwese hwe enthalpy:
\[
N₂(g) + 3 H₂O(g) – 3H₂(g) – 3/2 O₂(g) → 2NH₃(g) + O₂(g) – O₂(g) \kurudyi N₂(g) + 3H₂(g) → 2NH₃(g)
\]
Huwandu hwe enthalpy:
\[
ΔH_{total} = 180 + 904 + 726 = 1810 kJ/mol
\]
Saka, ΔH yemhinduro N₂(g) + 3H₂(g) → 2NH₃(g) i +1810kJ. Sezvo tichida kuti enthalpy ibudiswe (exothermic) tinoita kuti kukosha kwechigadzirwa kuve negative:
\[
ΔH_{total} = -46 kJ/mol
\]
Penutup
Chinyorwa chino chinokurukura matambudziko emuenzaniso anoshandisa Hess's Law kuverenga shanduko ye enthalpy ye reaction. Nekunzwisisa hwaro hwedzidziso uye kushandisa matanho ari mumatambudziko emuenzaniso, zvinotarisirwa kuti vaverengi vachanzwisisa zviri nyore pfungwa iyi uye vagokwanisa kuishandisa mumamiriro akasiyana-siyana anosanganisira kuverenga kwe thermochemical. Hess's Law haingori yakakosha mu chemistry yedzidzo chete asiwo inobatsira mukutsvagisa chemistry yeindasitiri uye mamwe mashandisirwo akasiyana-siyana musainzi netekinoroji.
