Concepts from Chemical Reaction Kinetics - Elements of Environmental Engineering: Thermodynamics and Kinetics - page 198

E XAMPLE 5.2 R EACTION R ATE C ONSTANT

The rate of loss of a VOC (chloroform) from water in an open beaker is said to be a
first-order process. The concentration in water was measured at various times as given
below:

t (min) [A]/[A] 0

0 1

20 0.5

40 0.23

60 0.11

80 0.05

100 0.03

Find the rate constant for the loss of chloroform from water.
First obtain a plot of ln [A]/[A] 0 versus t as in Figure 5.4. The slope of the plot
is 0.035 min − 1 with a correlation coefficient of 0.997. Hence the rate constant is
0.035 min − 1 .

1

y = -0.036153 x

0

-1

-2

-3

-4

0 20 40 60 80 100 120

t /min

FIGURE 5.4 Experimental points and data fit to a first-order reaction rate law.

5.3.3.1 Reversible Reactions

Thereactionratelawsdescribedabovediscountthepossibilityofreversereactionsand
will fail to give the overall rate of a process near equilibrium conditions. In the natural
environment such reactions are common. When the product concentration becomes
significant, the reverse reaction will also become significant near equilibrium. This