Zitsanzo za Mafunso Okhudza Kusintha kwa Enthalpy ndi Enthalpy
Enthalpy ndi lingaliro lofunika kwambiri mu thermodynamics ya mankhwala, lomwe limapezeka kawirikawiri m'mitu yosiyanasiyana ya chemistry, kuyambira machitidwe a mankhwala mpaka kusintha kwa magawo. M'nkhaniyi, tiwunikanso mavuto angapo a zitsanzo ndikukambirana za kusintha kwa enthalpy ndi enthalpy kuti tithe kumvetsetsa bwino lingaliroli.
Kumvetsetsa Enthalpy
Enthalpy (H) ndi mphamvu yonse mu dongosolo la thermodynamic. Sizimaphatikizapo mphamvu yamkati yokha yomwe imasungidwa mu tinthu tating'onoting'ono komanso mphamvu yomwe imafunika kuti tinthu tating'onoting'ono tipeze malo m'malo opanikizika. Enthalpy imayesedwa mu ma joules (J) mu International System (SI).
Mwa masamu, enthalpy imatanthauzidwa motere:
\[ H = U + PV \]
Kumene:
– \( H \) ndiye enthalpy
– \( U \) ndi mphamvu yamkati
– \( P \) ndi kupanikizika
– \( V \) ndi voliyumu
Kusintha kwa Enthalpy
Kusintha kwa enthalpy (\( \Delta H \)) kumachitika pamene mankhwala kapena njira zakuthupi zimachitika. Kusintha kwa enthalpy kumeneku kungatanthauzidwe ngati kuchuluka kwa kutentha komwe kumatulutsidwa kapena kuyamwa ndi dongosolo lomwe limapanikizika nthawi zonse. Mwa masamu:
\[ \Delta H = H_{\text{product}} – H_{\text{reactant}} \]
Zochitika za exothermic ndi zochitika zomwe zimatulutsa kutentha m'chilengedwe, ndipo muzochitika izi, \( \Delta H \) ndi zoipa. Pakadali pano, endothermic reaction ndi zomwe zimayamwa kutentha kuchokera ku chilengedwe, ndipo mu izi, \( \Delta H \) ili ndi phindu labwino.
Mafunso ndi Kukambirana Zitsanzo
Chitsanzo Funso 1: Kusintha kwa Enthalpy ya Kuyaka
Funso:
Amadziwika kuti kuyaka kwathunthu kwa mole imodzi ya methane (\(CH_4\)) kumapanga carbon dioxide (\(CO_2\)) ndi madzi (\(H_2O\)). Enthalpy ya deta yopangidwa ndi iyi:
– \( \Delta H_{{f, H_2O (l)}} = -285.8 \text{kJ/mol} \)
– \( \Delta H_{{f, CO_2 (g)}} = -393.5 \text{kJ/mol} \)
– \( \Delta H_{{f, CH_4 (g)}} = -74.8 \text{kJ/mol} \)
Werengerani kusintha kwa enthalpy (\( \Delta H \)) ya kuyaka kwa moto.
Kukambirana:
Kuyaka kwa methane ndi:
\[ CH_4 (g) + 2 O_2 (g) \kumanja CO_2 (g) + 2 H_2O (l) \]
Kusintha kwa enthalpy kwa reaction (\( \Delta H \)) kungawerengedwe pogwiritsa ntchito enthalpy ya mapangidwe:
\[ \Delta H = \Sigma \Delta H_f \text{products} – \Sigma \Delta H_f \text{reactants} \]
Chogulitsa:
\[ \Delta H_f (CO_2 (g)) = -393.5 \text{kJ/mol} \]
\[ \Delta H_f (H_2O (l)) = -285.8 \text{kJ/mol} \]
Chiwerengero chonse cha zinthu:
\[ (-393.5 \malemba{kJ/mol}) + 2\times(-285.8 \malemba{kJ/mol}) = -393.5 – 571.6 = -965.1 \malemba{kJ/mol} \]
Zoyambitsa:
\[ \Delta H_f (CH_4 (g)) = -74.8 \text{kJ/mol} \]
\[ \Delta H_f (O_2 (g)) = 0 \text{kJ/mol} \]
(Okisijeni mu mkhalidwe wake wamba ili ndi enthalpy ya kupanga zero.)
Chiwerengero chonse cha zinthu zomwe zimayambitsa matenda:
\[ (-74.8 \text{kJ/mol}) + 2\times(0 \text{kJ/mol}) = -74.8 \text{kJ/mol} \]
Kotero, kusintha kwa enthalpy (\( \Delta H \)) ndi:
\[ \Delta H = -965.1 \mawu{kJ/mol} – (-74.8 \ mawu{kJ/mol}) \]
\[\Delta H = -965.1 + 74.8 \]
\[ \Delta H = -890.3 \text{kJ/mol} \]
Kotero, kusintha kwa enthalpy kwa kuyaka kwa mole imodzi ya methane ndi \(-890.3 \text{kJ/mol}\).
Chitsanzo Funso 2: Kusintha kwa Enthalpy mu Machitidwe a Thupi
Funso:
Werengerani kusintha kwa enthalpy pamene magalamu 50 a ayezi (\(H_2O_{(s)}\)) pa 0°C asungunuka kukhala madzi (\(H_2O_{(l)}\)) pa 0°C. Amadziwika kuti kutentha kwa kusungunuka kwa ayezi (\( \Delta H_{\text{fus}} \)) ndi 6.01 kJ/mol ndipo kuchuluka kwa madzi ndi 18 g/mol.
Kukambirana:
Gawo loyamba ndikuwerengera chiwerengero cha ma moles a ayezi.
\[ \text{Moles of ice} = \frac{50 \text{g}}{18 \text{g/mol}} \approx 2.78 \text{mol} \]
Kenako timawerengera kusintha kwa enthalpy pakusungunula ayezi:
\[ \Delta H = n \cdot \Delta H_{\text{fus}} \]
\[ \Delta H = 2.78 \text{mol} \cdot 6.01 \text{kJ/mol} \]
\[ \Delta H \pafupifupi 16.7 \text{kJ} \]
Choncho, kusintha kwa enthalpy mukasungunula ayezi wa magalamu 50 pa 0°C kumakhala pafupifupi 16.7 kJ. Iyi ndi njira ya endothermic chifukwa ayeziyo imatenga kutentha kuti isanduke madzi.
Chitsanzo 3: Kuyankha kwa Hess
Funso:
Gwiritsani ntchito lamulo la Hess kuti mudziwe kusintha kwa enthalpy pa zotsatirazi:
\[ 2 C(graphite) + 3 H_2(g) \rightarrow C_2H_6(g) \]
Pali zochitika zingapo zomwe zimadziwika ndi kusintha kwawo kwa enthalpy:
1. \( C(graphite) + O_2(g) \rightarrow CO_2(g), \Delta H = -393.5 \text{kJ} \)
2. \( H_2(g) + \frac{1}{2}O_2(g) \rightarrow H_2O(l), \Delta H = -285.8 \text{kJ} \)
3. \( 2 C_2H_6(g) + 7 O_2(g) \rightarrow 4 CO_2(g) + 6 H_2O(l), \Delta H = -3119.6 \text{kJ} \)
Kukambirana:
Kuti tiwerenge kusintha kwa enthalpy (\( \Delta H \)) kwa reaction, tifunika kusintha ndikuchulukitsa zina mwa reactions kuti zigwirizane ndi target reaction.
Langkah-langkah:
1. Sinthani zomwe zimachitika \(C_2H_6 \rightarrow 2 CO_2 + 3 H_2O\):
\[2C_2H_6(g) + 7O_2(g) \muvi wakumanja 4 CO_2(g) + 6H_2O(l), \Delta H = -3119.6 \text{kJ}\]
Kubwereza ndi kugawa mayankho:
\[ 4CO_2(g) + 6H_2O(l) \muvi wakumanja 2C_2H_6(g) + 7O_2(g), \Delta H = 3119.6/2 = 1559.8 \mawu{kJ} \]
2. Kuyankha \(C \rightarrow CO_2\):
\[ 4C(graphite) + 4O_2(g) \rightarrow 4CO_2(g), \Delta H = 4 \times -393.5 = -1574 \text{kJ} \]
3. Kuyankha \(H_2\rightarrow H_2O\):
\[ 6H_2(g) + 3O_2(g) \muvi 6H_2O(l), \Delta H = 6 \nthawi -285.8 = -1714.8 \mawu{kJ} \]
Mukaphatikiza zonsezi, timapeza:
\[2C(graphite) + 3H_2(g) \muvi wa kumanja C_2H_6\]
\[ \Delta H = 1559.8 – 1574 – 1714.8 = -1729 \text{kJ}\]
Kotero, kusintha kwa enthalpy kwa momwe ma mole awiri a graphite amachitira ndi ma mole atatu a \(H_2\) ku \(C_2H_6(g)\) ndi -1729 kJ.
Motero, kumvetsetsa lingaliro la enthalpy ndi momwe limagwiritsidwira ntchito pa mitundu yosiyanasiyana ya machitidwe kumapereka chidziwitso cha momwe mphamvu imakhudzira kusintha kwa mankhwala ndi thupi. Mavuto omwe ali pamwambapa ndi zitsanzo zomwe zimagwiritsidwa ntchito nthawi zambiri mu maphunziro kuti zilimbikitse kumvetsetsa mfundo izi.
