Ch. 8 Thermochemistry 熱化學

Transcription

1 Ch. 8 Thermchemistry 熱化學 8-1: Principes eat Fw 1. State Prperties. Directin and Sin eat Fw 3. Manitude eat Fw 8-: Measurement eat Fw;Carimetry 1. Cee-Cup Carimeter. Bmb Carimeter 8-3: Enthapy Δ 8-4: Thermchemica Equatins 8-5: Enthapies rmatin 1. Meanin Δ 0. Cacuatin Δ 0 8-6: Bnd Enthapy 8-7: The irst aw thermdynamics 1. ΔU = q + w. Δ Versus ΔU; = U + RT n 1

2 8-1 Principes heat w Chemica reactin: System:reactants and prducts. Surrundins:the vesse in which the reactin takes pace and the air r ther materia in therma cntact with the reactin system. State prperty ( 狀態性質 ): Any thermdynamic prperty whse vaue r the prcess is independent the path. It depends ny n the state the system. 一性質與初態和終態有關, 與其過程和途徑無關. 例如 :cmpsitin, T and P 例 : 50.0 O( ) at 50, 1atm 50.0 O( ) at 80, 1atm X = X ina X initia eat w ( 熱流量 ; q) is nt a state prperty (nn-state prperty); its manitude depends n hw a prcess is carried ut. Nn-state prperty a system: 一性質與其過程和途徑有關. 如 : 功 (wrk; w); 熱流量 (heat w; q) Directin and Sin eat Fw: eat w (q) q: + when heat ws int the system rm the surrundins. 吸熱 q: - when heat ws ut the system int the surrundins. 放熱 An endthermic( 吸熱 ) prcess (q > 0) 例 : Os () O () q > 0

3 An exthermic( 放熱 ) prcess (q < 0) 例 : C + O CO + O q < 0 4 放熱至環境中 Manitude heat w: q: 單位 J, kj 1 ca = J 1 kca = kj q = C T ( T = T T ) ina C:heat capacity the system J K initia The amunt heat required t raise the temperature the system 1K. Fr a pure substance mass m q = m c T c : speciic heat capacity 比熱 c:the amunt heat required t raise the temperature ne ram a substance ne Kevin. J K C = m c Tabe 8.1 O (): c = 4.18 J ; O : c = 1.87 K J K Ex 8.1. Cmpare the amunt heat iven by 1.40 m iquid water when it cs rm t 10.0 t that iven when 1.40 m steam cs rm 00 t

4 Ans: q 1 = m c T c vaue rm Tabe 8.1. = (18.0 x 1.40) (4.18) ( ) = (5.8) x (4.18) x (-90.0) = J = kj q = m c T = (18.0 x 1.40) (1.87) (110 00) = (5.8) x (1.87) x (-90) = -446 J = -4.5 kj Steam ives ess heat than water when it cs. 8- Measurement eat w; Carimetry 熱卡計 Carimeter 卡計 : 測反應熱之儀器, 儀器內含水或其它已知比熱物質, 卡計可隔絕外界空氣對熱量之影響 q q reactin carimeter q reactin = - q = C T ca = - C carimeter ca = - m c T ca T Cee-cup Carimeter 4

5 Fi 8.. 實驗室用, pystyrene am cup 內含水, 外加溫度計攪拌棒 q reactin = -m c T ca = -m 4.18 T Ex 8.. Cacium chride, CaC, is added t canned veetabes t maintain the veetabes irmness. When added t water, it dissves: Ans: CaC s Ca aq C aq () + + A carimeter cntains 50.0 water at When 1.00 cacium chride is added t the carimeter, the temperature rises t Assume that a the heat iven by the reactin is transerred t the water. (a) Cacuate q r the reactin system. (b) w much CaC must be added t raise the temperature the sutin 9.00? 5

6 ( a) q = m c T q O reactin = ( ) = 734 J = - q O ca = -734 J (b) q = - m c T reactin ca = = J 1.00 : -734 = m : CaC m =.56 CaC Bmb carimeter 彈形卡計 Cee cup carimeter 不適合含氣體之反應及高溫產物之反應. bmb carimeter heavy-waed meta vesse 浸入水中 q = - q = C T reactin carineter ca C ca 可由一已知反應熱之反應測得之, 如下例 : 6

7 例 : 一反應放熱 93.3 kj, 而 Bmb carimeter 升溫由 0.00 至 kj = - C T C ca ca = - C ( ) ca 93.3 = = 9.33 kj K Ex 8.3. ydren chride is used in etchin semicnductrs. It can be prepared by reactin hydren and chrine ases. Ans: + C C () It is und that when 1.00 is made t react cmpetey with C in a bmb carimeter, the temperature in the bmb (heat capacity = 9.33 kj/k) rises rm 0.00 t 9.8. w much heat is evved by the reactin? q = -C T reactin ca = ( ) = kj 8-3 Enthapy 焓 ; At cnstant pressure (P = C), the heat w r the reactin system is equa t the dierence in enthapy () between prducts and reactants. P = C; q reactin = = - 生成物 反應物 Reactants < 0 放熱反應 >0 吸熱反應 Prducts Prducts Reactants reactin path reactin path 例 : C4 + O CO + O 例 : Os () O () < 0 放熱反應 > 0 吸熱反應 7

8 1.00 O( ) (5, 1atm) 1.00 O( ) (6, 1 atm) = 4.18 J = c; 比熱 8-4 Thermchemica equatins: A chemica equatin as shws the enthapy reatin between prducts and reactants. N NO () s N ( aq) + NO ( aq) N NO q = 351 J 4 3 reactin r 1 me N NO 4 3 = 351 J = kj r 1.00 N NO 4 3 = (0.351) (80.05) = +8.1 kj N NO () s N ( aq) + NO ( aq) = +8.1 kj C C = -185 kj 8

9 Thermchemica equatins: 1. P = C, + endthermic 吸熱反應 exthermic 放熱反應. 平衡常數代表 me 數 1 me ( ) + 1 me C me C () = -185 kj 反應熱之值隨平衡係數值改變而變. 3. 反應物及生成物狀態需明確標示, (s), (), (aq). 4. 一般未標明下, 指 5 狀況下. Rues Thermchemistry 1. The manitude prduct. is directy prprtina t the amunt reactant r + C C = -185 kj C C = (-185 kj) = -9.5 kj Ex 8.4. The Bunsen burners in yur abs are ueed by natura as, which is msty methane, C 4. The thermchemica equatin r the cmbustin (burnin in xyen) methane is C4 + O CO + O() = kj Cacuate when (a) 5.00 C 4 react with an excess xyen. (b).00 L O at 49.0 and 78 mm react with an excess methane. (c).00 L C 4 react with 5.00 L O in a reactin vesse kept at 5 and 1.00 atm. Fwed the idea as behavir. Ans: 9

10 ( a) = = -78 kj m C PV (78/760).00 (b) n O = = = m RT ( ) kj = = kj m O (c) P = C and T = C; V n n : n = 1 : C is the imitin reaent. C O 4 PV n C = = = m 4 RT (5 + 73) = = -7.7 kj 1 m C s heat usin us heat vaprizatin vap Tabe 8.. 正反應 = - 逆反應 Os () O () = kj O () Os () = kj Ex 8.5. Given Ans: + O O () = kj Cacuate r the equatin 1 O () O O O () = = 85.8 kj 1 O () O + = -(-85.8) kj = kj 3. The vaue r a reactin is the same whether it ccurs in ne step r in a series step. 10

11 反應熱 與反應物及生成物狀態有關, = - 生成物 ; 與反應步驟無關 狀態性質. 反應物 ess s aw: undamenta basis thermdynamics as appied t chemica reactins. Speciic chemica chanes are accmpanied by a characteristic chane in enery. New chemica chanes can be devised by cmbin knwn chemica chanes. This is dne aebraicay. The chane in enery the cmbined reactin is the equivaent aebraic cmbinatin the enery chanes the cmpnent chemica reactin. ess s aw 黑斯定律 1) 反應熱依化學反應之初態及終態而定, 與中間反應過程無關. ) 熱化學反應與代數方程式一般, 可以彼此加減. Ex 8.6. Carbn mnxide, CO, is a pisnus as. It can be btained by burnin Ans: carbn in a imited amunt xyen. Given (1) Cs () + O() CO = kj 1 () CO + O CO() = kj Cacuate r the reactin 1 C (s) + 1 (1) - 1 (): O () CO =? C (s) + O CO CO ( ) CO () + 1 O 1 C (s) + O CO () = = 1 (-393.5) - (-566.0) = kj

12 Thermchemistry 重點整理 : 1. 與反應物及生成物之量成正比. 正反應 = - 逆反應 3. 與反應過程無關, 僅與反應初態及終態有關. 8-5 Enthapies Frmatin: 利用生成焓可以更方便計算反應之. = 生成物 - 反應物 Meanin : Standard mar enthapy rmatin 標準莫耳生成焓 : The enthapy chane when ne me cmpund is rmed at P = 1 atm, T = 5 rm the eements. 1 A (s) (5 ) + C (1 atm, 5 ) AC (s) = kj m (s) 1 N (1 atm, 5 ) + O (1 atm, 5 ) AC (5 ) = kj; NO ( ) = kj m = kj NO (1 atm, 5 ) Tabe 8.3 1

13 常溫常壓下 (1 atm, 5 ), 所有穩定狀態元素之莫耳生成焓 = 0 Br = O = 0 Cacuatin standard enthapy chane. = prducts - reac tan ts Thermite ( 鋁熱劑 ): A (s) + O ) Fe ( 3 s Fe (s) + A O ) ( 3 s = 生成物 - 反應物 = Fe s + 3 () A O () s -[ ] A( s) + Fe O = ( ) (-84.) = kj 3 s. 平衡係數, 必需列入計算 13

14 A (s) + 3 ( aq) Cu + 3 A + ( aq) + 3 Cu (s) = 生成物 - 反應物 3 = A + ( aq) - 3 Cu + ( aq) = (-531.0) - 3 (+64.8) = kj Ex 8.7. Benzene, C 6 6, used in the manuacture pastics, is a carcinen aectin the bne marrw. Ln-term expsure has been shwn t cause eukemia and the bd disrders. The cmbustin benzene is iven by the win equatin: Ans: 15 C 66( ) + O 6 CO + 3 O (a) Cacuate the heat rmatin benzene. (b) Cacuate r the reactin 1 CO + 6 O () C () + 15O (c) Cacuate 6 6 r the reactin 15 C 66( ) + O 6 CO + 3 O Given that vap r benzene at 5 C is 33.6 kj/m ; r water at 5 C is 44.0 kj/m. vap = kj (a) = 生成物 - 反應物 = [ 6 CO + 3 O( ) ] [ ] C = [ 6 ( 393.5) + 3 ( 85.8) ] C 6 6 C = [( 361) + ( 857.4) ] = kj m (b) 15 [ C 66( ) + O ] x (-) 1 CO + 6 O () C () + 15O 6 6 = (-367.4) (-) = kj 14

15 15 (c) (1) C O 6 CO + 3 O 1 = kj () O( ) + O( ) = kj (3) () C (1) + 3 () - 1 (3): 15 C 66( ) + O + 3 O( ) + C 6 6 C CO + 3 O + 3 O( ) + C 6 6 = vap = 33.6 kj 15 C 66( ) + = 1 1 O 6 CO + 3 O = (-367.4) + 3 (44.0) (33.6) = kj Ex 8.8. Sdium carbnate is a white pwder used in the manuacture ass. When hydrchric acid is added t a sutin sdium carbnate, carbn dixide Ans: as is rmed. The equatin r the reactin is ( aq) + CO ( aq) CO + O () + 3 (a) Cacuate r the thermchemica equatin. (b) Cacuate when 5.0 ml M C is added t sdium carbnate. (a) = 生成物 - 反應物 + = [ CO + O( ) ] [ ( aq) + CO ] 3 aq = [( 393.5) + ( 85.8) ] [ (0.00) + ( 677.1) ] 15

16 (b) = -. kj 5.00 n C = n + = V M = = m 1000.kJ m + 3 = m = kj Bnd enthapy 鍵結焓 : 均為 + 值 When ne me bnds is brken in the ases state. ( ) ( ) = 436 kj - bnd enthapy = 436 kj C ( ) C() = 43 kj C-C bnd enthapy = 43 kj 8-7 The First aw Thermdynamics 熱力學第一定律 Thermchemistry is a branch thermdynamics. Thermdynamics distinuishes between tw types enery ne these is heat (q); the ther is wrk (w). Wrk incudes a rms enery except heat. The aw cnservatin enery: 能量不滅定律 U = U system surrundins The irst aw Thermdynamics: In any prcess, the tta chane in enery a system, U is equa t the sum the heat, q, and the wrk, w, transer between the system and the surrundins. U = q + w Fr an isated system, the tta enery the system remains cnstant. 16

17 U = q + w Isated system 獨立系統 : et ut the system. A system des nt aw matter r enery cme in r Ex 8-9: Cacuate U a as r a prcess in which the as. a) absrbs 0 J heat and des 1 J wrk by expandin. b) evves 30 J heat and has 5 J wrk dne n it as it cntacts. Ans: U = q + w a) q = +0 J w = -1J U = +0 + (-1) = +8 J b) q = -30 J w= +5 J U = = + J C + 4 O CO + O U = -885 kj U q w 本生燈 -885 kj -890 kj +5 kj 汽車引擎 -885 kj -665 kj -0 kj 燃料電池 * -885 kj -67 kj -818 kj * 以功率而言, 此項最佳. versus U Cee-cup carimeter P = C = q P Bmb carimeter V = C w = 0 U = q V = U + PV 1 me 5 PV = (5+73) = 4.5 L-atm kj =.48 kj 1 L-atm = kj = U + PV 17

18 = U + [( PV ) ( PV ] 產物 ) 反應物 = U + nrt n : 氣體物質莫耳數改變量 5 下, C 4 + O CO + O () U = -885 kj n = 1- (1 + ) = - m R:8.314 J T:98 K m. k = U + nrt = (-885 kj) + (-) = (-885 kj) + ( J) = (-885 kj) + (-5.0 kj) = -890 kj = -890 kj; U = -885 kj 大多反應, 其 w 佔不到 1%, 可忽略. Ex Cacuate and U at 5 r the reactin takes pace when an xyacetyene trch is used. Ans: 5 C + O CO + O = 生成物 - 反應物 = [ CO ( ) + O ( )] [ C ] = [ ( 393.5) + ( 41.8) ] (6.7) = kj 5 n = ( + 1) (1 + ) = -0.5 m = U + RT n 18

19 U = - RT n = (-0.5) (8.314) (5 + 73) = kj + 1. kj = kj 19