First Order Reactions
Definition
A reaction
in which the rate of reaction is proportional to the concentration of reactants
raised to power one is known as first order reaction.
Or
If the rate
of reaction is determined by the concentration of only one reactant, then it is
called 1st order reaction
Also note
that in first order reaction, rate of reaction is proportional to the
concentration of only one reactant and is independent of the concentrations of
others if present.
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Kinetics of first order reaction
R → P
At t=0 a 0
After time t a-x x
e.q. 3.1
eq.3.2To
find value of z consider that at initial time t=0, the concentration is x=0.
So, putting values of x and t in e.q. 3.2 we got
Putting value of "z" in e.q. 3.2 we got
Or ln
(a-x) = –Kt + lna e.q.
3.3
 |
Figure 3.1:
graph for first order reaction (equation 3.3) |
Rearranging e.q. 3.3 we got straight line equation for first order reaction.
e.q. 3.4
Figure 3.2: straight line graph for first order reaction (equation 3.4) |
Rate constant for first order
reaction and its unit
From e.q. 3.4 rate constant is
Unit of rate constant will be K= s-1
K= min-1, year-1 etc.
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