Ngā Tauira Pātai e Matapaki ana i ngā Huringa Enthalpy me te Enthalpy
He ariā matua te enthalpy i roto i te thermodynamics matū, e kitea pinepine ana i roto i ngā kaupapa matū maha, mai i ngā tauhohenga matū ki ngā huringa āhua. I roto i tēnei tuhinga, ka arotakehia e mātou ētahi tauira raruraru, ka matapakihia hoki ngā huringa enthalpy me te enthalpy hei āwhina i a mātou ki te mārama ake ki te ariā.
Te Mārama ki te Enthalpy
Ko te enthalpy (H) te tapeke o te pūngao i roto i tētahi pūnaha thermodynamic. Ehara i te mea ko te pūngao ā-roto anake e rongoatia ana i roto i ngā matūriki engari ko te pūngao e hiahiatia ana hei waihanga wāhi mō ngā matūriki i roto i tētahi taiao pēhanga kua hoatu. Ka inehia te enthalpy i roto i ngā joule (J) i roto i te Pūnaha Ao (SI).
I roto i te pāngarau, ko te enthalpy te tikanga:
\[ H = U + PV \]
kāore i te mana:
– Ko te enthalpy te \( H \)
– Ko te pūngao ā-roto ko \( U \)
– Ko te pēhanga te \( P \)
– Ko te rōrahi te \( V \)
Huringa Enthalpy
Ka puta te panonitanga enthalpy (\( \Delta H \)) ina puta he tauhohenga matū, he tukanga ā-tinana rānei. Ka taea te tautuhi i tēnei panonitanga enthalpy ko te nui o te wera e tukuna ana, e mimitihia ana rānei e tētahi pūnaha i te pēhanga pumau. Mā te pāngarau:
\[ \Delta H = H_{\kuputuhi{hua}} – H_{\kuputuhi{tauhohenga}} \]
Ko ngā tauhohenga exothermic he tauhohenga e tuku ana i te wera ki te taiao, ā, i roto i ēnei tauhohenga, he kino te \( \Delta H \). I taua wā, ko te tauhohenga endothermic he tauhohenga e mimiti ana i te wera mai i te taiao, ā, i roto i tēnei tauhohenga, he uara pai te \( \Delta H \).
Ngā Pātai Tauira me te Kōrero
Tauira Pātai 1: Te Huringa o te Enthalpy o te Mura
Pātai:
E mōhiotia ana ko te tahunga katoa o te 1 mole o te methane (\(CH_4\)) ka puta he hauhā waro (\(CO_2\)) me te wai (\(H_2O\)). Ko te enthalpy o te hanganga koia tēnei:
– \( \Delta H_{{f, H_2O (l)}} = -285.8 \text{kJ/mol} \)
– \( \Delta H_{{f, CO_2 (g)}} = -393.5 \text{kJ/mol} \)
– \( \Delta H_{{f, CH_4 (g)}} = -74.8 \text{kJ/mol} \)
Tātaihia te panonitanga enthalpy (\( \Delta H \)) o te tauhohenga mura.
Kōrero:
Ko te tauhohenga tahunga o te methane ko:
\[ CH_4 (g) + 2 O_2 (g) \perematau CO_2 (g) + 2 H_2O (l) \]
Ka taea te tatau i te huringa enthalpy o te tauhohenga (\( \Delta H \)) mā te whakamahi i te enthalpy o te hanganga:
\[ \Delta H = \Sigma \Delta H_f \kuputuhi{hua} – \Sigma \Delta H_f \kuputuhi{tauhohenga} \]
Hua:
\[ \Delta H_f (CO_2 (g)) = -393.5 \text{kJ/mol} \]
\[ \Delta H_f (H_2O (l)) = -285.8 \text{kJ/mol} \]
Te enthalpy katoa o ngā hua:
\[ (-393.5 \kJ/mol}) + 2\times(-285.8 \kJ/mol}) = -393.5 – 571.6 = -965.1 \kJ/mol} \]
Ngā matū tauhohe:
\[ \Delta H_f (CH_4 (g)) = -74.8 \text{kJ/mol} \]
\[ \Delta H_f (O_2 (g)) = 0 \text{kJ/mol} \]
(Ko te hāora i roto i tōna āhua paerewa he kore te enthalpy o te hanganga.)
Te enthalpy katoa o ngā matū tauhohe:
\[ (-74.8 \text{kJ/mol}) + 2\times(0 \text{kJ/mol}) = -74.8 \text{kJ/mol} \]
Nō reira, ko te huringa o te enthalpy (\( \Delta H \)) ko:
\[ \Delta H = -965.1 \text{kJ/mol} – (-74.8 \text{kJ/mol}) \]
\[ \Delta H = -965.1 + 74.8 \]
\[ \Delta H = -890.3 \text{kJ/mol} \]
Nō reira, ko te huringa enthalpy mō te tahunga o te 1 mole o te methane ko \(-890.3 \text{kJ/mol}\).
Tauira Pātai 2: Ngā Huringa Enthalpy i roto i ngā Tukanga Ā-Tinana
Pātai:
Tātaihia te panoni enthalpy ina rewahia te 50 karamu o te hukapapa (\(H_2O_{(s)}\)) i te 0°C ki roto i te wai (\(H_2O_{(l)}\)) i te 0°C. E mōhiotia ana ko te wera o te rewa o te hukapapa (\( \Delta H_{\text{fus}} \)) he 6.01 kJ/mol, ā, ko te papatipu molar o te wai he 18 karamu/mol.
Kōrero:
Ko te taahiraa tuatahi ko te tatau i te maha o ngā mole o te huka.
\[ \text{Ngā ira hukapapa} = \frac{50 \text{g}}{18 \text{g/mol}} \approx 2.78 \text{mol} \]
Muri iho ka tatauhia e mātou te huringa enthalpy mō te whakarewa i te huka:
\[ \Delta H = n \cdot \Delta H_{\text{fus}} \]
\[ \Delta H = 2.78 \text{mol} \cdot 6.01 \text{kJ/mol} \]
\[ \Delta H \tata ki te 16.7 \text{kJ} \]
Nō reira, ko te huringa enthalpy ina rewa te 50 karamu o te hukapapa i te 0°C he tata ki te 16.7 kJ. He tukanga endothermic tēnei nā te mea ka mimiti te hukapapa i te wera ka huri hei wai.
Tauira 3: Tauhohenga a Hess
Pātai:
Whakamahia te ture a Hess hei whakatau i te huringa enthalpy mō te tauhohenga e whai ake nei:
\[ 2 C(kāwhati) + 3 H_2(g) \rightarrow C_2H_6(g) \]
E mōhiotia ana ētahi tauhohenga me ō rātou huringa enthalpy:
1. \( C(kāwhata) + O_2(g) \rightarrow CO_2(g), \Delta H = -393.5 \text{kJ} \)
2. \( H_2(g) + \frac{1}{2}O_2(g) \rightarrow H_2O(l), \Delta H = -285.8 \text{kJ} \)
3. \( 2 C_2H_6(g) + 7 O_2(g) \rightarrow 4 CO_2(g) + 6 H_2O(l), \Delta H = -3119.6 \text{kJ} \)
Kōrero:
Hei tatau i te huringa enthalpy (\( \Delta H \)) o te tauhohenga, me huripokitia, me whakareatia hoki ētahi o ngā tauhohenga kia taurite ki te tauhohenga ūnga.
Ngā Hipanga:
1. Hurihia te tauhohenga \(C_2H_6 \rightarrow 2 CO_2 + 3 H_2O\):
\[2C_2H_6(g) + 7O_2(g) \perematau 4 CO_2(g) + 6H_2O(l), \Delta H = -3119.6 \text{kJ}\]
Whakahurihia, whakawehea hoki ngā tauhohenga:
\[ 4CO_2(g) + 6H_2O(l) \perematau 2C_2H_6(g) + 7O_2(g), \Delta H = 3119.6/2 = 1559.8 \text{kJ} \]
2. Tauhohenga \(C \rightarrow CO_2\):
\[ 4C(karāpiti) + 4O_2(g) \rightarrow 4CO_2(g), \Delta H = 4 \times -393.5 = -1574 \text{kJ} \]
3. Tauhohenga \(H_2\rightarrow H_2O\):
\[ 6H_2(g) + 3O_2(g) \pere matau 6H_2O(l), \Delta H = 6 \wa -285.8 = -1714.8 \text{kJ} \]
Mā te whakakotahi i ngā mea katoa, ka whiwhi tātou:
\[2C(graphite) + 3H_2(g) \perematau C_2H_6\]
\[ \Delta H = 1559.8 – 1574 – 1714.8 = -1729 \text{kJ}\]
Nō reira, ko te huringa enthalpy o te tauhohenga o ngā mole graphite e 2 me ngā mole 3 o \(H_2\) ki \(C_2H_6(g)\) he -1729 kJ.
Nō reira, mā te mārama ki te ariā o te enthalpy me tōna whakamahinga ki ngā momo tauhohenga ka mārama ki te whai wāhi o te pūngao ki ngā huringa matū me ngā huringa ā-tinana. Ko ngā raruraru i runga ake nei he tauira e whakamahia pinepine ana i roto i te marautanga hei whakapakari i te māramatanga ki ēnei ariā.
