Nā nīnau hoʻohālike a me ke kūkākūkā ʻana o nā kaulike Thermochemical
ʻO ka Thermochemistry kahi lālā o ke kemika e aʻo ana i nā loli ikehu e kū mai ana i ka wā o nā hopena kemika, ʻoiai ka hoʻoili wela. Pili ka Thermochemistry i nā manaʻo e like me ka enthalpy, entropy, a me ka ikehu manuahi ʻo Gibbs, i hoʻohana ʻia e wānana i ke kuhikuhi a me ka spontaneity o nā hopena. Ma kēia ʻatikala, e ʻimi mākou i kekahi mau pilikia hoʻohālike a kūkākūkā i nā kaulike thermochemical.
Nā Manaʻo Kumu o ka Thermochemistry
Ma mua o ke komo ʻana i nā nīnau hoʻohālike a me kā lākou kūkākūkā ʻana, he mea nui e ʻike i kekahi mau manaʻo kumu o ka thermochemistry:
1. Enthalpy (H): ʻO Enthalpy kahi ʻano ikehu i loko o kahi ʻōnaehana i ana ʻia ma lalo o nā kūlana kaomi mau. Hiki ke hōʻike ʻia ka loli o ka enthalpy (\( \Delta H \)) penei:
\[ \Delta H = H_{huahana} – H_{mea hoʻouluulu} \]
2. Nā Hana Endothermic a me Exothermic:
– ʻO nā hopena exothermic nā hopena e hoʻokuʻu i ka wela i loko o ke kaiapuni (\( \Delta H < 0 \)). - ʻO nā hopena endothermic nā hopena e omo i ka wela mai ke kaiapuni (\( \Delta H > 0 \)).
3. Ke Kānāwai o Hess: Ke ʻōlelo nei ke Kānāwai o Hess ua like ka loli enthalpy holoʻokoʻa o kahi hopena kemika inā hana ʻia ka hopena ma hoʻokahi ʻanuʻu a i ʻole kekahi mau ʻanuʻu. Hiki ke ʻōlelo ʻia penei:
\[ \Delta H_{huina} = \Delta H_1 + \Delta H_2 + … + \Delta H_n \]
Nā Nīnau Laʻana a me ke Kūkākūkā
Laʻana Nīnau 1: Ke helu ʻana i ka loli Enthalpy
Hāʻawi ʻia nā hopena aʻe:
\[ 2H_2(g) + O_2(g) \arrow 2H_2O(l) \]
Inā ʻike ʻia ʻo ka loli enthalpy o ka hoʻokumu ʻana (\( \Delta H_f \)) o ka wai he -285.8 kJ/mol. E helu i ka loli enthalpy holoʻokoʻa no ka hopena.
Kūkākūkā:
Hiki ke helu ʻia ka loli enthalpy o kahi hopena (\( \Delta H_{reaction} \)) me ka hoʻohana ʻana i ka loli enthalpy o ka hoʻokumu ʻia ʻana o nā huahana a me nā reactants.
Ua ʻike ʻia:
– \[ \Delta H_f(H_2O(l)) = -285.8 \text{ kJ/mol} \]
Ma muli o ka hoʻokumu ʻia ʻana o ʻelua mau mole o ka wai, ʻo ka loli enthalpy holoʻokoʻa o ka hopena:
\[ \Delta H_{reaction} = 2(-285.8 \text{ kJ/mol}) \]
\[ \Delta H_{reaction} = -571.6 \text{ kJ} \]
No laila, ʻo ka loli enthalpy holoʻokoʻa no kēia hopena he -571.6 kJ. He exothermic kēia hopena no ka mea he maikaʻi ʻole ʻo \( \Delta H \).
Laʻana Nīnau 2: Hoʻohana ʻana i ke Kānāwai o Hess
Hāʻawi ʻia nā hopena aʻe:
\[ C(s) + O_2(g) \rightarrow CO_2(g) \hspace{2mm} \text{(1)} \]
\[ C(s) + 1/2 O_2(g) \rightarrow CO(g) \hspace{2mm} \text{(2)} \]
CO(g) + 1/2 O_2(g) CO_2(g) space{2mm} kikokikona{(3)}
Ua ʻike ʻia:
– \(\Delta H_1 = -393.5 \text{ kJ}\)
– \(\Delta H_2 = -110.5 \text{ kJ}\)
E helu i ka loli enthalpy no ka hopena (3).
Kūkākūkā:
E hoʻohana i ke Kānāwai o Hess e hoʻoholo ai i ka loli enthalpy no ka hopena (3). E hoʻomaopopo hiki ke haku ʻia ka hopena (3) me nā hopena (1) a me (2):
\[ \text{Reaction } (3): CO(g) + 1/2 O_2(g) \rightarrow CO_2(g) \]
E hoʻohuli i ka hopena (2) e hoʻohana i ke Kānāwai o Hess:
ʻO CO_2(g) C(s) + O_2(g) space{2mm} (ʻaoʻao hoʻohuli 1)), ʻO Delta H = +393.5 kJ
ʻO C(s) + 1/2 O_2(g) CO(g) space{2mm}, Delta H = -110.5 kJ}
I kēia manawa e hoʻohui i nā hopena:
CO_2(g) C(s) + O_2(g) + 1/2 O_2(g) CO(g) + 1/2 O_2(g)
CO_2(g) C(s) + O_2(g) CO(g) + 1/2 O_2(g)
E hoʻohui i nā loli enthalpy:
\[ \Delta H_{reaction} = 393.5 – 110.5 \text{ kJ}\]
\[ \Delta H_{reaction} = 283.0 \text{ kJ}\]
No laila, no ka hopena \(CO(g) + 1/2 O_2(g) \rightarrow CO_2(g) \), ʻo ka loli enthalpy he -283.0 kJ.
Laʻana Nīnau 3: Ka Hana ʻana o ka Calorimeter
Hāʻawi ʻia he 100 mL o 1.0 M hydrochloric acid (HCl) a me 100 mL o 1.0 M sodium hydroxide (NaOH). Ke hui ʻia nā mea ʻelua i loko o kahi calorimeter, piʻi ka mahana mai 25.0 °C a i 31.0 °C. Inā ʻo ka mana wela o ka wai he 4.18 J/g°C a ʻo ka nui o ka wai he 1.0 g/mL, e helu i ka loli enthalpy o ka neutralization.
Kūkākūkā:
ʻanuʻu:
1. E helu i ka nuipa o ka hopena:
\[ \text{Ka nui o ka wai} = 100 \text{ mL} + 100 \text{ mL} = 200 \text{ mL} \]
\[ \text{Mass} = 200 \text{ g} \] (no ka mea, ʻo ka nui o ka wai hoʻoheheʻe he 1 g/mL)
2. E helu i ka loli o ka mahana:
\[ \Delta T = 31.0 \text{ °C} – 25.0 \text{ °C} = 6.0 \text{ °C} \]
3. E helu i ka ikehu i omo ʻia e ka hopena:
\[ q = m \cdot c \cdot \Delta T \]
\[ q = 200 \text{ g} \times 4.18 \text{ J/g°C} \times 6.0 \text{ °C} \]
\[ q = 5016 \kikokikona{ J} \]
\[ q = 5.016 \kikokikona{ kJ} \]
4. E helu i ka loli enthalpy:
\[ \Delta H = \frac{q_{\text{solution}}}{\text{mol HCl}} \]
Ke noʻonoʻo nei ua like nā mole o HCl a me NaOH:
\[ \text{Nā Mole HCl} = 1.0 \text{ M} \times 0.100 \text{ L} = 0.100 \text{ mol} \]
\[ \Delta H = \frac{5.016 \text{ kJ}}{0.100 \text{ mol}} \]
\[ \Delta H = -50.16 \text{ kJ/mol} \]
No laila, ʻo ka loli enthalpy no ka neutralization o HCl a me NaOH he -50.16 kJ/mol, e hōʻike ana i kahi hopena exothermic.
Ka hopena
He lālā koʻikoʻi o ke kemika ka Thermochemistry e kōkua iā mākou e hoʻomaopopo pehea e hoʻololi ʻia ai ka ikehu a hoʻololi ʻia i nā hopena kemika. Ma ka hoʻomaopopo ʻana i nā manaʻo kumu e like me ka enthalpy a me ke kānāwai o Hess, a me ka hiki ke hoʻopili iā lākou i nā pilikia kūpono, hiki iā mākou ke wānana i nā loli ikehu e hana ʻia i nā hopena kemika like ʻole. Ua hōʻike kēia ʻatikala i kekahi mau pilikia hoʻohālike e manaʻolana e kōkua i ka hoʻoikaika ʻana i kou ʻike i nā kaulike thermochemical.
