Tauira o tētahi Pātai Kōrero mō te Pūngao Here
Pendahuluan
Ko te pūngao here he ariā matua i roto i te matū e āwhina ana i a tātou ki te mārama ki te pūngao e hiahiatia ana hei wawahi i te here i roto i te ngota. Ki te kī māmā noa, ko te pūngao here te nui o te pūngao e hiahiatia ana hei wehe i ngā ngota e rua e herea ana i roto i te ngota kia motuhake. I roto i tēnei tuhinga, ka mārama tātou ki te ariā o te pūngao here mā roto i ētahi tauira rapanga me te matapakinga mō ēnei.
Te Ariā o te Pūngao Here
Ko te pūngao here e whakaatuhia ana i roto i ngā kilojoules mō ia mole (kJ/mol), ā, he rerekē te pūngao here o ia momo here matū. Hei tauira, he rerekē te pūngao here mō te here C-H kotahi (waro-hauwai) i te pūngao here mō te here C=O takirua (waro-hāora).
Ko te whārite e whakamahia whānuitia ana hei tatau i te huringa enthalpy o tētahi tauhohenga (\(\Delta H\)) i runga i ngā pūngao hononga ko:
\[
\Delta H = \Sigma D_{\text{ngā matū tauhohe}} – \Sigma D_{\text{ngā hua}}
\]
Ko \(D_{\text{reactants}}\) me \(D_{\text{products}}\) ngā pūngao here e uru ana ki ngā tauhohenga me ngā hua. Arā, ko te tapeke o ngā pūngao here i roto i ngā tauhohenga tangohia te tapeke o ngā pūngao here i roto i ngā hua.
Ngā Pātai Tauira me te Kōrero
Pātai 1
E mōhiotia ana ko te pūngao here toharite mō ngā here e whai ake nei ko:
– Herenga HH: 436 kJ/mol
– Herenga O=O: 498 kJ/mol
– Herenga HO: 463 kJ/mol
Tātaihia te huringa enthalpy (\(\Delta H\)) mō te tauhohenga e whai ake nei:
\[
2H_2(g) + O_2(g) \perematau 2H_2O(g)
\]
Kōrero:
Ko te taahiraa tuatahi ko te tuhi i te tauhohenga me te tatau i te maha o ngā hononga kei roto i ngā matū tauhohenga me ngā hua.
Mō ngā matū tauhohe:
– E 2 ngā ngota o te \(H_2\) ko te tikanga e 2 ngā here HH
– Ko te tikanga o te 1 ngota ngota o te \(O_2\) he 1 te here O=O
Mō ngā hua:
– Ko te tikanga o ngā ngota ngota 2 (H_2O) he 4 ngā here HO
Te pūngao here katoa i roto i ngā matū tauhohe:
\[
2 \times \text{Pūngao here HH} + 1 \times \text{Pūngao here O=O}
\]
\[
= 2 \whakareatia ki te 436 + 1 \whakareatia ki te 498
\]
\[
= 872 + 498
\]
\[
= 1370 kJ/mol
\]
Te pūngao here katoa i roto i te hua:
\[
4 \times \text{pūngao here HO}
\]
\[
= 4 \whakareatia ki te 463
\]
\[
= 1852 kJ/mol
\]
Huringa enthalpy (\(\Delta H\)):
\[
\Delta H = \Sigma D_{\text{ngā matū tauhohe}} – \Sigma D_{\text{ngā hua}}
\]
\[
= 1370 \text{ kJ/mol} – 1852 \text{ kJ/mol}
\]
\[
= -482 kJ/mol
\]
Nō reira, ko te huringa enthalpy mō te tauhohenga ko \(-482\) kJ/mol.
Pātai 2
E whakaarohia ana ko ngā pūngao hononga e whai ake nei e mōhiotia ana:
– Herenga CH: 414 kJ/mol
– C=Te herenga C: 612 kJ/mol
– Herenga HH: 436 kJ/mol
Tātaihia te huringa enthalpy (\(\Delta H\)) mō te tauhohenga e whai ake nei:
\[
C_2H_4(g) + H_2(g) \pere matau C_2H_6(g)
\]
Kōrero:
Ko te taahiraa tuatahi ko te tuhi i te tauhohenga me te tatau i te maha o ngā hononga kei roto i ngā matū tauhohenga me ngā hua.
Mō ngā matū tauhohe:
– E 4 ngā hononga CH me te 1 hononga C=C i roto i te ngota ngota 1 o \(C_2H_4\) (ethylene)
– Kotahi te hononga HH o te ngota ngota o \(H_2\)
Mō ngā hua:
– E 6 ngā here CH me te 1 here CC i roto i te ngota ngota kotahi o te \(C_2H_6\) (etana)
Te pūngao here katoa i roto i ngā matū tauhohe:
\[
4 \times \text{Pūngao here CH} + 1 \times \text{Pūngao here C=C} + 1 \times \text{Pūngao here HH}
\]
\[
= 4 \whakareatia 414 + 1 \whakareatia 612 + 1 \whakareatia 436
\]
\[
= 1656 + 612 + 436
\]
\[
= 2704 kJ/mol
\]
Te pūngao here katoa i roto i te hua:
\[
6 \times \text{pūngao here CH} + 1 \times \text{pūngao here CC}
\]
\[
= 6 \whakareatia ki te 414 + 1 \whakareatia ki te 348
\]
\[
= 2484 + 348
\]
\[
= 2832 kJ/mol
\]
Huringa enthalpy (\(\Delta H\)):
\[
\Delta H = \Sigma D_{\text{ngā matū tauhohe}} – \Sigma D_{\text{ngā hua}}
\]
\[
= 2704 \text{ kJ/mol} – 2832 \text{ kJ/mol}
\]
\[
= -128 kJ/mol
\]
Nō reira, ko te huringa enthalpy mō te tauhohenga ko \(-128\) kJ/mol.
Whakamutunga
Ko te ariā o te pūngao here he mea nui i roto i te ako i ngā tauhohenga matū me ō rātou huringa enthalpy. I roto i tēnei tuhinga, kua matapakihia e mātou ētahi tauira raruraru e rua e whakaatu ana me pēhea te tatau i ngā huringa enthalpy mō ngā tauhohenga mā te whakamahi i te pūngao here. He mea nui tēnei māramatanga i roto i te whānuitanga o ngā tono matū, mai i te hanga rauropi ki te whanaketanga wahie. Ka taea te whakatutuki i tētahi māramatanga hohonu ake mā te mahi auau me te tūhura i ngā momo tauhohenga matū.
Whakamahia ngā tikanga kua whakaahuahia i roto i tēnei tuhinga hei aratohu mō te whakaoti rapanga pūngao hononga ā muri ake nei, ā, whakaarohia hoki ētahi atu rauemi ako hei whakahōhonu ake i tō mōhiotanga ki te matū pūngao hononga.
