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Exercise B - To determine the effect of inadequate mixing
on the reaction rate
Theory
The rate of reaction is measured by the amount of reactants converted to products in
a unit of time. In order for reaction to occur, particles must come into contact and this
contact must result in interaction. The rate of reaction depends on the collision
frequency and collision efficiency of particles of the reacting substances. These
factors are optimised by thorough mixing of the reactants using stirrers and baffles
within the reactor. Inefficient mixing will result in reduced reaction rates.
Considering the reaction between sodium hydroxide and ethyl acetate, if the initial
concentrations are equal (both a
0
) and the conversion (X
a
) then the concentrations
are as follows:
NaOH + CH
3
COOC
2
H
5
→
C
2
H
5
OH + CH
3
COONa
(a
0
-X
a
) (a
0
-X
a
) (X
a
) (X
a
)
Method
Repeat Exercise A after removing the baffles from the reactor. This is achieved by
removing the conductivity and temperature probes then removing the lid of the
reactor. The baffle arrangement simply lifts out.
Repeat the experiment with baffles removed and no stirring action.
Three sets of data will be obtained:
a. Stirred reactor with baffle (see Exercise A)
b. Stirred reactor, no baffle
c. Un-stirred reactor, no baffle
Graphs of the reaction conversion with time can be plotted using the data logger (or
using the manual readings obtained if not using the logger).
Comment on the results obtained. How did removal of the baffle affect the reaction
rate? What effect does stirring have on the reaction rate?
