This document discusses methods for determining reaction rates and orders in physical chemistry. It describes differential and integral methods, including graphs of concentration versus time used to determine rate coefficients and reaction orders. Specific reaction orders are examined, such as zero order, first order, and second order reactions. Examples of each type are provided. Third order reactions involving interactions of two and three molecules are also discussed.

1. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
01/30/15 1
Dr. M. Masykuri, M.Si.
Chemical Education Study Program
Teacher Training and Educational Studies
Sebelas Maret University (UNS)
Website: http://masykuri.staf.fkip.uns.ac.id,
email: mmasykuri@yahoo.com
Solo, Sep 2010
Kimia Fisika IV

2. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
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. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
Macam Metode
Metode Penentuan Tetapan Laju:
Metode relaksasi, metode analisis guegenheim

4. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
Metode Diferensial
• Data dikumpulkan sebagai laju perubahan
konsentrasi/waktu terhadap konsentrasi reaktan.
• Contoh dasar persamaan bagi reaksi dengan 2 reaktan:
aA + bB → produk
qp
BAk
dt
Ad
r ][][
][
=−=
]ln[]ln[ln
][
lnln BqApk
dt
Ad
r ++=





−=
• Dibuat kurva ln r terhadap ln [A] atau ln [B]

5. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
Metode Diferensial
]ln[]ln[ln
][
lnln BqApk
dt
Ad
r ++=





−=
• Kurva ln r terhadap ln [A]
]ln['lnln Apkr +=
Orde reaksi terhadap A = p, diperoleh dari slope = tg α
Tetapan laju k, diperoleh dari intersep grafik
Orde reaksi terhadap A = p, diperoleh dari slope = tg α
Tetapan laju k, diperoleh dari intersep grafik
Slope = tg α
= p
]ln[ln'ln BqkkIntersep +==

6. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
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 0,800 8 0,382
2 0,647 10 0,329
4 0,534 12 0,286
6 0,448 14 0,252
a. Tentukan orde reaksi
terhadap A sampai kelipatan
½ terdekat
b. Tentukan harga tetapan laju
reaksi k dengan satuannya
yang tepat

7. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
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
– Prde ketiga

8. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
Metode Integral
• The rate of the reaction is independent of the
concentration of the reacting substance
Zero Order Reactions
A → products
∫∫ −=
−=
=−
dtkAd
k
dt
Ad
k
dt
Ad
A
A
][
][ 0
][
][
][
[A]t - [A]0 = - kt
The reaction half-time t1/2 is the time
required for the concentration to
decrease to one-half of its initial value.

9. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
Metode Integral
Zero Order Reactions
Grafik [A] versus t,
Persamaan grafik,
Slope = - k
Intersep = [A]0
Waktu paruh,

10. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
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
∫∫ −=
−=
=−
dtk
A
Ad
kdt
A
Ad
Ak
dt
Ad
A
A
][
][ 0
][
][
][
][
][
][
Examples:
• decay of radioactive nuclei fluorescence
• decay of electronically excited molecules
• isomerization of cyclobutene to butadiene
• milk turns sour when left out overnight

11. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
Metode Integral
First Order Reactions
Grafik ln [A] versus t,
Persamaan grafik,
Buktikan bahwa,

12. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
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 componenta) Second order in one component
A → products
b) First order in each of two componentsb) First order in each of two components
A +B → products

13. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
Metode Integral
Second Order Reactions
a) Second order in one componenta) Second order in one component
A → products

14. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
b) First order in each of two componentsb) 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

15. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
b) First order in each of two componentsb) 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

16. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
Metode Integral
Third Order Reactions
Several possible cases. Could be:
(a) three identical chemical molecules interact simultaneously
(unusual)
(a) three identical chemical molecules interact simultaneously
(unusual)
(b) two molecules of one species interact with one of another(b) two molecules of one species interact with one of another
(c) three different chemical species interact with each other(c) three different chemical species interact with each other

17. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
Metode Integral
Third Order Reactions
(b) two molecules of one species interact with one of another(b) two molecules of one species interact with one of another
Example: recombination of homonuclear molecules such as iodine
Mechanism:

18. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
Metode Integral
Third Order Reactions
(b) two molecules of one species interact with one of another(b) two molecules of one species interact with one of another
Example: recombination of homonuclear molecules such as iodine

19. Teacher Training and Educational Studies
Sebelas Maret University
M. Masykuri_Physical Chemistry IV
Sep, 2010
Metode Integral
Third Order Reactions
(c) three different chemical species interact with each other(c) three different chemical species interact with each other
Very important example: formation of ozone in the
stratospheric ozone layer,
(M = air)