Nā nīnau hoʻohālike e kūkākūkā ana i ka Enthalpy a me nā loli Enthalpy
He manaʻo koʻikoʻi ka Enthalpy i ka thermodynamics kemika, i loaʻa pinepine ʻia i nā kumuhana kemika like ʻole, mai nā hopena kemika a hiki i nā loli pae. Ma kēia ʻatikala, e nānā mākou i kekahi mau pilikia hoʻohālike a kūkākūkā i ka enthalpy a me nā loli enthalpy e kōkua iā mākou e hoʻomaopopo maikaʻi i ke kumumanaʻo.
Ke Hoʻomaopopo nei i ka Enthalpy
ʻO ka Enthalpy (H) ka nui o ka ikehu i loko o kahi ʻōnaehana thermodynamic. ʻAʻole ia e komo wale i ka ikehu kūloko i mālama ʻia i loko o nā ʻāpana akā ʻo ka ikehu hoʻi e pono ai e hana i kahi no nā ʻāpana i loko o kahi ʻano kaomi i hāʻawi ʻia. Ana ʻia ka Enthalpy ma joules (J) ma ka International System (SI).
Ma ke ʻano makemakika, ua wehewehe ʻia ka enthalpy penei:
\[ H = U + PV \]
Ma hea:
– ʻO \( H \) ka enthalpy
– ʻO \( U \) ka ikehu kūloko
– ʻo \( P \) ke kaomi
– ʻO \( V \) ka nui
Hoʻololi Enthalpy
Hana ʻia ka loli enthalpy (\( \Delta H \)) ke hana ʻia kahi hopena kemika a i ʻole ke kaʻina hana kino. Hiki ke wehewehe ʻia kēia loli enthalpy ʻo ia ka nui o ka wela i hoʻokuʻu ʻia a i ʻole i omo ʻia e kahi ʻōnaehana ma ke kaomi mau. Ma ke ʻano makemakika:
\[ \Delta H = H_{\text{product}} – H_{\text{reactant}} \]
ʻO nā hopena exothermic nā hopena e hoʻokuʻu i ka wela i loko o ke kaiapuni, a ma ia mau hopena, \( \Delta H \) he maikaʻi ʻole. I kēia manawa, ʻo ka hopena endothermic kahi hopena e omo i ka wela mai ke kaiapuni, a ma kēia hopena, he waiwai maikaʻi ko \( \Delta H \).
Nā Nīnau Laʻana a me ke Kūkākūkā
Laʻana Nīnau 1: Hoʻololi i ka Enthalpy o ke kuni ʻana
Nīnau:
Ua ʻike ʻia ʻo ka puhi piha ʻana o 1 mole o ka methane (\(CH_4\)) e hoʻopuka i ke kalapona ʻokikene (\(CO_2\)) a me ka wai (\(H_2O\)). Penei ka ʻikepili enthalpy o ka hoʻokumu ʻana:
– \( \Delta H_{{f, H_2O (l)}} = -285.8 \text{kJ/mol} \)
– \( \Delta H_{{f, CO_2 (g)}} = -393.5 \text{kJ/mol} \)
– \( \Delta H_{{f, CH_4 (g)}} = -74.8 \text{kJ/mol} \)
E helu i ka loli enthalpy (\( \Delta H \)) o ka hopena puhi.
Kūkākūkā:
ʻO ke ʻano o ka hopena puhi ʻana o ka methane:
\[ CH_4 (g) + 2 O_2 (g) \arrow CO_2 (g) + 2 H_2O (l) \]
Hiki ke helu ʻia ka loli enthalpy o ka hopena (\( \Delta H \)) me ka hoʻohana ʻana i ka enthalpy o ka hoʻokumu ʻana:
\[ \Delta H = \Sigma \Delta H_f \text{products} – \Sigma \Delta H_f \text{reactants} \]
Huahana:
\[ \Delta H_f (CO_2 (g)) = -393.5 \text{kJ/mol} \]
\[ \Delta H_f (H_2O (l)) = -285.8 \text{kJ/mol} \]
Huina enthalpy o nā huahana:
\[ (-393.5 \text{kJ/mol}) + 2\times(-285.8 \text{kJ/mol}) = -393.5 – 571.6 = -965.1 \text{kJ/mol} \]
Nā mea hana:
\[ \Delta H_f (CH_4 (g)) = -74.8 \text{kJ/mol} \]
\[ \Delta H_f (O_2 (g)) = 0 \text{kJ/mol} \]
(ʻO ka oxygen ma kona kūlana maʻamau he enthalpy o ka hoʻokumu ʻana o ka zero.)
Huina enthalpy o nā mea hana:
\[ (-74.8 \text{kJ/mol}) + 2\times(0 \text{kJ/mol}) = -74.8 \text{kJ/mol} \]
No laila, ʻo ka loli o ka enthalpy (\( \Delta H \)) penei:
\[ \Delta H = -965.1 \text{kJ/mol} – (-74.8 \text{kJ/mol}) \]
\[ \Delta H = -965.1 + 74.8 \]
\[ \Delta H = -890.3 \text{kJ/mol} \]
No laila, ʻo ka loli enthalpy no ke kuni ʻana o 1 mole o ka methane he \(-890.3 \text{kJ/mol}\).
Laʻana Nīnau 2: Nā Hoʻololi Enthalpy i nā Kaʻina Hana Kino
Nīnau:
E helu i ka loli enthalpy ke hoʻoheheʻe ʻia he 50 gram o ka hau (\(H_2O_{(s)}\)) ma 0°C i loko o ka wai (\(H_2O_{(l)}\)) ma 0°C. Ua ʻike ʻia ʻo ka wela o ka hoʻoheheʻe ʻana o ka hau (\( \Delta H_{\text{fus}} \)) he 6.01 kJ/mol a ʻo ka nuipa molar o ka wai he 18 g/mol.
Kūkākūkā:
ʻO ka hana mua, ʻo ia ka helu ʻana i ka helu o nā mole o ka hau.
\[ \text{Nā mole o ka hau} = \frac{50 \text{g}}{18 \text{g/mol}} \approx 2.78 \text{mol} \]
A laila e helu mākou i ka loli enthalpy no ka hoʻoheheʻe ʻana i ka hau:
\[ \Delta H = n \cdot \Delta H_{\text{fus}} \]
\[ \Delta H = 2.78 \text{mol} \cdot 6.01 \text{kJ/mol} \]
\[ \Delta H \approx 16.7 \text{kJ} \]
No laila, ʻo ka loli enthalpy i ka wā e hoʻoheheʻe ai i 50 grams o ka hau ma 0°C ma kahi o 16.7 kJ. He hana endothermic kēia no ka mea hoʻopili ka hau i ka wela e lilo i wai.
Laʻana 3: Ka Hana a Hess
Nīnau:
E hoʻohana i ke kānāwai o Hess e hoʻoholo ai i ka loli enthalpy no kēia hopena:
\[ 2 C(graphite) + 3 H_2(g) \rightarrow C_2H_6(g) \]
Ua ʻike ʻia kekahi mau hopena me kā lākou mau loli 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. \( 2 C_2H_6(g) + 7 O_2(g) \rightarrow 4 CO_2(g) + 6 H_2O(l), \Delta H = -3119.6 \text{kJ} \)
Kūkākūkā:
No ka helu ʻana i ka loli enthalpy (\( \Delta H \)) o ka hopena, pono mākou e hoʻohuli a hoʻonui i kekahi o nā hopena e hoʻohālikelike i ka hopena i manaʻo ʻia.
ʻanuʻu:
1. E hoʻololi i ka hopena \(C_2H_6 \rightarrow 2 CO_2 + 3 H_2O\):
\[2C_2H_6(g) + 7O_2(g) \arrow 4 CO_2(g) + 6H_2O(l), \Delta H = -3119.6 \text{kJ}\]
Hoʻohuli a puʻunaue i nā hopena:
\[ 4CO_2(g) + 6H_2O(l) \arrow 2C_2H_6(g) + 7O_2(g), \Delta H = 3119.6/2 = 1559.8 \text{kJ} \]
2. Hana \(C \rightarrow CO_2\):
\[ 4C(graphite) + 4O_2(g) \rightarrow 4CO_2(g), \Delta H = 4 \times -393.5 = -1574 \text{kJ} \]
3. Hana \(H_2\rightarrow H_2O\):
\[ 6H_2(g) + 3O_2(g) \arrow 6H_2O(l), \Delta H = 6 \manawa -285.8 = -1714.8 \text{kJ} \]
Ke hoʻohui nei i nā mea a pau, loaʻa iā mākou:
\[2C(graphite) + 3H_2(g) \arrow C_2H_6\]
\[ \Delta H = 1559.8 – 1574 – 1714.8 = -1729 \text{kJ}\]
No laila, ʻo ka loli enthalpy o ka hopena o 2 moles o ka graphite a me 3 moles o \(H_2\) i \(C_2H_6(g)\) he -1729 kJ.
No laila, ʻo ka hoʻomaopopo ʻana i ke kumumanaʻo o ka enthalpy a me kāna hoʻopili ʻana i nā ʻano hopena like ʻole e hāʻawi i ka ʻike i ke ʻano o ka ikehu e pili ana i nā loli kemika a me ke kino. ʻO nā pilikia ma luna nei kekahi mau laʻana i hoʻohana pinepine ʻia i loko o ka papa hana e hoʻoikaika i ka hoʻomaopopo ʻana i kēia mau manaʻo.
