Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

1.4 References 8
2. Formal kinetics
2.1 Definitions and conventions
2.1.1 The rate of a chemical reaction
I
Rate of a simple reaction of type A + B → C+D:
≡− A
= − B
=+ C
=+ D
= − [A]
= − [B]
=+ [C]
=+ [D]
(2.1)
(2.2)
We will usually write the concentrations of a species A by using square brackets, i.e.,
[A] and understand that [A] is time dependent, i.e., [A ()].
I Definition of the rate of reaction: 12 Using the standard convention for the signs
of the stoichiometric coefficients of the reactants (−1) and products (+1), we write a
generic chemical reaction as
1 B 1 + 2 B 2 + → B + +1 B +1 + (2.3)
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The progress of the reaction from reactants to products can be described using the
reaction progress coordinate :
=
(2.4)
The time dependence leads to the definition of the reaction rate.
Definition 2.1: The reaction rate is defined as
≡ 1
(2.5)
For the above reaction, therefore,
= − 1 1
| 1 | = − 1 2
| 2 | = =+ 1
| | =+ 1 +1
| +1 |
= (2.6)
I Units: 13
• SI unit for the reaction rate:
[] = mol m 3 s (2.7)
12 Reaction rate = Reaktionsgeschwindigkeit. Von manchen Schulen wird auch der Begriff “Reaktionsrate”
verwendet. Die bevorzugte “einzig wahre korrekte Übersetzung” wird von der jeweils anderen
Seite sehr ernst genommen, allerdings gilt in Kiel in dieser Hinsicht Waffenstillstand.
13 For general information on the SI system see (Mills 1988) or (Homann 1995).