Arrhenius equation Guide, Meaning , Facts, Information and Description
The
Arrhenius equation predicts the rate of a
chemical reaction at a certain temperature, given the
activation energy and chance of successful collision of
molecules. It is named after Swedish scientist
Svante Arrhenius.
The average amount of thermal energy that molecules possess at a certain temperature is equal to RT, where R is the molar gas constant. The fraction of molecules that have enough energy to overcome the energy barrier—those with energy over the activation energy, EA (joule)— depends exponentially on the ratio of the activation to thermal energy. This forms the Arrhenius equation:
where
k (
m/s) is the
rate constant for the reaction and the
A factor or the
frequency factor A (m/s) is a constant specific to each reaction that depends on the chance the molecules will collide in the correct orientation. It can be seen that either increasing the temperature or decreasing the
activation energy (for example through the use of
catalysts) will result in an increase in rate of reaction.
A more general form of Arrhenius equation is
where
A' can be determined with
statistical mechanics and it depends on the shape of the energy surface of the complex (the
dissolved ions).
ΔG‡ (joule) is the
free energy. For simple cases,
where
κ is the transmission coefficient (a value between
zero and
unity); is
Boltzmanns constant;
T is the
temperature;
h is
Plancks constant.
Taking the natural logarithm of the Arrhenius equation yields
The modified Arrhenius equation yields an equation of the form y=mx+b, where
-
-
-
So, when a reaction has a rate constant which obeys the Arrhenius equation, a plot of ln(k) versus T
-1 gives a straight line. Slope and intercept can be used to determine E and A characteristics.
See also
Kinetics
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