Metode Differensial Integral KIMIA ANALITIK

Metode Differensial Integral.

1. METODE PENENTUAN TETAPAN LAJU & ORDE REAKSI Dr. M. Masykuri, M.Si. Chemical Education Study Program Teacher Training and Educational Studies Sebelas Maret Universit y ( UNS ) Website: http://masykuri.staf.fkip.uns.ac.id, email: [email protected] Solo, Sep 2010 Kimia Fisika IV Modul 3

2. Rate of Reaction Consider a chemical reaction having the overall stoichiometry: aA + bB → cC + dD The Rate of Reaction is defined as Experimentally we find that k = rate coefficient Ci = Concentration of Reactant “i” or [i] γi = Order of reaction with respect to reactant “i”

3. 3 Reaction Orders Zero-order First-order Second-order Third-order Negative First-order 1.5-order No simple order

4. 4 Rate Laws Reaction Rate Law

5. Macam Metode Metode Penentuan Tetapan Laju: 1. Metode Diferensial 2. Metode Integral 3. Metode Waktu Paruh 4. Metode Lain Metode relaksasi, metode analisis guegenheim

6. Metode Diferensial Data dikumpulkan sebagai laju perubahan konsentrasi/waktu terhadap konsentrasi reaktan. Contoh dasar persamaan bagi reaksi dengan 2 reaktan: aA + bB → produk Dibuat kurva ln r terhadap ln [A] atau ln [B]

7. Metode Diferensial Kurva ln r terhadap ln [A] Orde reaksi terhadap A = p, diperoleh dari slope = tg  Tetapan laju k, diperoleh dari intersep grafik Slope = tg  = p

8. Metode Diferensial Data konsentrasi zat A pada reaksi, yang dikatalisis suatu katalis C sebagai fungsi waktu diketahui sbb: A → produk Contoh: t (menit) A (M) t (menit) A (M) 0,800 8 0,382 2 0,647 10 0,329 4 0,534 12 0,286 6 0,448 14 0,252 Tentukan orde reaksi terhadap A sampai kelipatan ½ terdekat Tentukan harga tetapan laju reaksi k dengan satuannya yang tepat

9. Metode Diferensial Reaksi antara A dan B berikut: yang lajunya diberikan sebagai r =k (A) p (B) q diamati pada 2 keadaan berikut : (A) = 10,00 M dan (B) = 0,408 M (kons. A tetap) (A) = 0,550 M dan (B) = 10,00 M (kons. B tetap) A + B → produk Latihan : t (menit) B (M) t (menit) B (M) 0, 408 16 0, 234 4 0, 355 20 0, 204 8 0, 309 24 0, 178 12 0, 269 28 0, 155 Hasil pengamatan Kondisi 1): t (menit) A (M) t (menit) A (M) 0, 550 16 0, 485 4 0, 533 20 0, 470 8 0, 516 24 0, 457 12 0, 500 28 0, 443 Hasil pengamatan Kondisi 2): TUGAS I dikumpulkan minggu depan

10. Metode Diferensial Tentukan k, p dan q?????? Latihan :

11. Metode Integral Bersifat trial and error (empiris) , yaitu dengan memasukkan data pada persamaan laju bentuk integral. Jika harga k relatif tetap (konstan), maka orde reaksinya sesuai. Penentuan empiris orde reaksi terhadap reaktan: Orde nol Orde pertama Orde kedua tipe I Orde kedua tipe II Or de ketiga

12. Metode Integral The rate of the reaction is independent of the concentration of the reacting substance Zero Order Reactions A → products [A] t - [A] = - kt The reaction half-time t 1/2 is the time required for the concentration to decrease to one-half of its initial value.

13. Metode Integral Zero Order Reactions Grafik [A] versus t, Persamaan grafik, Slope = - k Intersep = [A] Waktu paruh,

14. Metode Integral First Order Reactions The rate of the reaction is proportional to the first power of the concentration of the reacting substance (order = 1) A → products Examples: decay of radioactive nuclei fluorescence decay of electronically excited molecules isomerization of cyclobutene to butadiene milk turns sour when left out overnight

15. Metode Integral First Order Reactions Grafik ln [A] versus t, Persamaan grafik, Buktikan bahwa,

16. 16 First-Order Reactions Half-life: First-order reaction The time needed for [A] to drop to half its value Independent of [A] o A useful indication for the chemical reaction rate

17. Metode Integral Second Order Reactions The rate of the reaction is proportional to the second power of the concentration of one reactant or to the first power of the concentrations of two reactants (order = 2) a) Second order in one component A → products b) First order in each of two components A +B → products

18. Metode Integral Second Order Reactions a) Second order in one component A → products

19. 19 Second-Order Reactions define

20. 20 A plot of 1/[ A ] versus t gives a strait line of slope k A if Second-Order Reactions

21. 21 { [A] -1 } { t } Second-order reaction: 1/[A] vs t (17.16) Half-life: Second-order reaction with r = k[A] 2 Second-Order Reactions

22. 22 Second-order reaction with r = k[A] 2 First-order reaction with r = k[A] (17.18) Three variables

23. b) First order in each of two components Metode Integral Second Order Reactions A +B → products Special cases: i) [A]o = [B]o ii) [B]o <<[A]o

24. b) First order in each of two components Metode Integral Second Order Reactions Special cases (cont.): i) [A]o = [B]o ii) [B]o <<[A]o This is like 2nd order in one component Where, This is called a pseudo 1st order reaction

25. 25 x =0 when t =0 Second-Order Reactions

26. Second-Order Reactions

27. If [A] o = [B] o Half-life: Second-Order Reactions

28. Metode Integral Third Order Reactions Several possible cases. Could be: (a) three identical chemical molecules interact simultaneously (unusual) (b) two molecules of one species interact with one of another (c) three different chemical species interact with each other

29. Metode Integral Third Order Reactions (b) two molecules of one species interact with one of another Example: recombination of homonuclear molecules such as iodine Mechanism:

30. Metode Integral Third Order Reactions (b) two molecules of one species interact with one of another Example: recombination of homonuclear molecules such as iodine

31. Metode Integral Third Order Reactions (c) three different chemical species interact with each other Very important example: formation of ozone in the stratospheric ozone layer, (M = air)

32. 32 Third-Order Reactions Untuk Reaksi orde 3, ada 4 tipe reaksi: 1 2 3 4 Contoh penurunan pers. Utk reaksi orde 3 tipe 1:

33. 33 nth-Order Reaction Consider Integration gives For n  1 For n  1

34. 34 For n  1 For n = 1 Half-life: For n = nth-Order Reaction

35. Metode Integral Flow diagram:

36. Metode Integral Order Reaction Rate Law t 1/2 A  P 1 A  P 2 A  P n 2 A  P

37. Terimakasih