Chapter07 - Applied Science Department(ASD Centre for...

PCE 0015
Chemistry for Engineers
Foundation in Engineering
ONLINE NOTES
Chapter 7
REACTION KINETICS AND EQUILIBRIUM
FOSEE , MULTIMEDIA UNIVERSITY
(436821-T)
MELAKA CAMPUS, JALAN AYER KEROH LAMA, 75450 MELAKA, MALAYSIA.
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URL: http://fosee.mmu.edu.my/~asd/
Applied Science Department
(ASD)
Centre for Foundation Studies and Extension Education
(FOSEE)

PCE0015 Chemistry For Engineers Chapter 7
7.1 The Rate of a Reaction
7.2 The Rate Law
7.3 Relation Between Reactant Concentration and Time
7.4 Reaction Mechanism
7.5 Catalysis
7.6 The Concept of Equilibrium
7.7 Factors That Affect Chemical Equilibrium
Upon completion of this chapter, you should be able to:
1. Understand the rate of a reaction. It is the change in the concentration of a
reactants or products over time. The rate is not constant, but carries continuously
as concentration change.
2. Express rate law : the relationship of the rate of a reaction to the rate constant and
the concentrations of the reactants raised to appropriate powers.
3. Understand the relation between reactant concentration and time.
4. Define reaction mechanism. If one step in a reaction mechanism is much slower
than all other steps, it is the rate-determining step.
5. Elaborate types of catalyst and its functions : homogeneous catalyst and
heterogeneous catalyst.
6. Understand the concept of equilibrium. A chemical equilibrium process in which
all reactants and products are in the same phase is homogeneous. If the reactants
and products are not all in the same phase, the equilibrium is heterogeneous.
7. Express the factors that affect the chemical equilibrium : Le Châtelier’s Principle.
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HST/MAM 2/ 18

PCE0015 Chemistry For Engineers Chapter 7
7.1 THE RATE OF A REACTION
Chemical kinetics is the area of chemistry concerned with the speeds , or rates, at which
a chemical reaction occurs . Kinetics refers to the rate of a reaction, or the reaction rate ,
which is the change in the concentration of a reactant or a product with time (M/s).
Any reaction can be represented by the general equation
A (reactants)  B (products)
This equation tell us that during the course of a reaction, reactants are consumed while
products are formed. As a results, we can follow the progress of a reaction by monitoring
either the decrease in concentration of the A (reactants) or the increase in concentration
of the B (products) as shown in figure below.
In general, it is more convenient to express the reaction rate in terms of change in
concentration with time. Thus for the reaction A  B we can express the rate as
∆ [A] ∆ [B]
rate = - or rate =
∆ t ∆ t
where ∆ [A] and ∆ [B] are the changes in concentration (molarity) over a time period ∆ t.
Because the concentration of A decreases during the time interval, ∆ [A] is a negative
quantity. The rate of a reaction is a positive quantity, so a minus sign is needed in the rate
expression to make the rate positive. On the other hand, the rate of product formation
does not require a minus sign because ∆ [B] is a positive quantity (the concentration of B
increases with time). These rates are