Zitsanzo za Mafunso Okhudza Malamulo a Hess
Pendauluan
Lamulo la Hess, lotchedwa dzina la katswiri wa sayansi ya zamankhwala waku Russia Germain Henri Hess, ndi limodzi mwa mfundo zazikulu za thermodynamics ya mankhwala okhudzana ndi mphamvu ya zochita za mankhwala. Lamuloli limati kuchuluka kwa kutentha (mphamvu) komwe kumapangidwa kapena kuyamwa mu zochita za mankhwala sikudalira njira yomwe yatengedwa koma kokha pamikhalidwe yoyambirira komanso yomaliza ya dongosololi. Lamulo lofunikirali ndi lothandiza kwambiri powerengera kusintha kwa enthalpy (ΔH) ya zochita zomwe zimakhala zovuta kuziyeza mwachindunji.
Lamulo la Hess ndi lofunika kwambiri chifukwa limatithandiza kugwiritsa ntchito enthalpy yokhazikika kapena kusintha kwa enthalpy kwa reaction ina yodziwika bwino kuti tipeze kusintha kwa enthalpy kwa reaction yomwe siingathe kuyezedwa mosavuta. Munkhaniyi, tiwona zitsanzo zingapo za mavuto ndikukambirana za kugwiritsa ntchito Lamulo la Hess.
Chiphunzitso choyambira
Lamulo la Hess lingapangidwe motere:
Ngati kusintha kwa mankhwala kungachitike m'magawo angapo, ndiye kuti kusintha konse kwa enthalpy (ΔH_total) ndi chiwonkhetso cha kusintha kwa enthalpy (ΔH) pa gawo lililonse. Mwa masamu, imapangidwa motere:
ΔH_total = Σ ΔH_stage
Izi zikutanthauza kuti mutha kupeza enthalpy ya yankho motere:
``
Kuyankha A → Chogulitsa
|
ΔH1
Kuyankha B → Chogulitsa
|
ΔH2
Kenako, ΔH_total (A → Product) = ΔH1 + ΔH2
``
Tisanalowe mu mafunso achitsanzo, pali mawu angapo omwe ayenera kumvedwa:
1. Enthalpy (H): Muyeso wa mphamvu yonse ya dongosolo lomwe lili pansi pa kupanikizika kosalekeza.
2. ΔH (Kusintha kwa Enthalpy): Kusintha kwa enthalpy pakati pa ma reactants ndi zinthu.
3. Standard Enthalpy of Formation (ΔHf°): Kusintha kwa enthalpy pamene mole imodzi ya compound imapangidwa kuchokera ku zinthu zake mu standard states.
Mafunso ndi Kukambirana Zitsanzo
Chitsanzo Funso 1: Kugwiritsa Ntchito Enthalpy ya Kupanga
Funso:
Werengerani reaction enthalpy ya kuyaka kwa methane (CH₄) kutengera deta yotsatirayi ya kusintha kwa kapangidwe ka 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 (chifukwa mpweya wa okosijeni womwe uli mu mkhalidwe wake wamba uli ndi enthalpy yopangidwa ndi 0)
Kuyaka kwa Methane:
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)
Kukambirana:
1. Lembani momwe zinthu zimachitikira komanso momwe enthalpy imapangikira:
\[
ΔH_{reaction} = ∑ΔH_{product} – ∑ΔH_{reactant}
\]
2. Sinthani enthalpy yokhazikika ya mfundo zopangira mu equation:
\[
ΔH_{reaction} = [ΔHf° (CO₂) + 2 ΔHf° (H₂O)] – [ΔHf°(CH₄) + 2 ΔHf°(O₂)]
\]
3. M'malo mwa mfundo zodziwika bwino:
\[
ΔH_{reaction} = [(-393.5) + 2 (-285.8)] – [(-74.8) + 2 (0)]
\]
4. Kuwerengera mwatsatanetsatane:
\[
ΔH_{reaction} = [-393.5 + (-571.6)] – [-74.8 + 0]
\]
\[
ΔH_{reaction} = -965.1 + 74.8
\]
\[
ΔH_{reaction} = -890.3 kJ/mol
\]
Kotero, kusintha kwa enthalpy kwa kuyaka kwa methane ndi -890.3 kJ/mol. Mtengo woipa umasonyeza kuti kuyambikako ndi exothermic (kutulutsa mphamvu).
Chitsanzo Chachiwiri: Kugwiritsa Ntchito Mayankho Ochokera
Funso:
Werengerani reaction enthalpy ya reaction yotsatirayi:
N₂(g) + 3H₂(g) → 2NH₃(g)
Poganizira zochitika zitatu ndi kusintha kwa enthalpy motere:
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
Kukambirana:
1. Fotokozani momwe zinthuzo zimachitikira mu mawonekedwe olunjika omwe angakonzedwenso:
Yankho la cholinga:
N₂(g) + 3H₂(g) → 2NH₃(g)
Tiyenera kusintha momwe zinthu zilili kuti tikwaniritse zomwe tafotokozazi.
2. Kusanthula kwa zochita zokhudzana ndi NH₃:
Chigamulo 2 chili ndi NH₃, koma chigamulocho ndi kugawa NH₃ kukhala NO ndi H₂O. Chifukwa chake, sinthani izi:
2NO(g) + 3H₂O(g) → 2NH₃(g) + O₂(g), ΔH = +904 kJ
3. Kenako, tiyenera kuchotsa O₂(g):
Pachifukwa ichi, timagwiritsa ntchito reaction (1):
N₂(g) + O₂(g) → 2NO(g), ΔH = 180 kJ
M'malo mwake, tikufunika 2NO kuti tipange. Izi zikadali chimodzimodzi.
4. Werengerani enthalpy ya H₂O(g):
Onjezani reverse reaction (3) katatu mu equation:
3[H₂O(g) → H₂(g) + 1/2O₂(g), ΔH = +242 kJ]
Khalani:
3H₂O(g) → 3H₂(g) + 3/2 O₂(g), ΔH = +726 kJ
5. Phatikizani ndi kulinganiza ma equation:
\[
N₂(g) + O₂(g) → 2NO(g), ΔH = 180 kJ
+
2NO(g) + 3 H₂O(g) → 2NH₃(g) + O₂(g), ΔH = +904 kJ
+
3H₂O(g) → 3H₂(g) + 3/2 O₂(g), ΔH = +726 kJ
\]
Pofotokoza mwachidule momwe zinthu zilili, tingathe kunyalanyaza zinthu zomwe zimawonekera mbali zonse ziwiri ndikuwerengera kuchuluka kwa enthalpy yonse.
6. Werengani kuchuluka kwa enthalpy:
\[
N₂(g) + 3 H₂O(g) – 3H₂(g) – 3/2 O₂(g) → 2NH₃(g) + O₂(g) – O₂(g) \motsatira chakumanja N₂(g) + 3H₂(g) → 2NH₃(g)
\]
Mphamvu yonse ya enthalpy:
\[
ΔH_{total} = 180 + 904 + 726 = 1810 kJ/mol
\]
Kotero, ΔH ya reaction N₂(g) + 3H₂(g) → 2NH₃(g) ndi +1810kJ. Popeza tikufuna kutulutsa enthalpy (exothermic) timapanga mtengo wa chinthucho kukhala woipa:
\[
ΔH_{total} = -46 kJ/mol
\]
Kutseka
Nkhaniyi ikufotokoza za mavuto omwe amagwiritsa ntchito lamulo la Hess powerengera kusintha kwa enthalpy kwa zomwe zimachitika. Mwa kumvetsetsa maziko a chiphunzitso ndikugwiritsa ntchito masitepe omwe ali mu mavuto a zitsanzo, tikukhulupirira kuti owerenga adzamvetsa mosavuta lingaliro ili ndikukhala ndi mwayi woligwiritsa ntchito pazochitika zosiyanasiyana zokhudzana ndi kuwerengera kwa thermochemical. Lamulo la Hess silofunika kokha mu chemistry yamaphunziro komanso lothandiza pa kafukufuku wa chemistry yamakampani ndi ntchito zina zosiyanasiyana mu sayansi ndi ukadaulo.
