Ask A Scientist© Chemistry Archive

 > >    name         david
 > >    status       student
 > >    age          19

 > >    Question -   why would one expect that a reaction carried out at a
 > > higher temperature would proceed at a faster rate?


What's required for a chemical reaction to occur -- the reactants must come
in contact and they must have sufficient energy to react.  How will
temperature impact these things?
Bradburn
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This is because the molecules are moving faster
at a higher temperature, and collide with each
other more often. Thus, reactive collisions
happen more often per second, and this increases
the reaction rate.


best regards,
prof. topper
the cooper union
new york, ny

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    Because temperature can be interpreted as the average kinetic
energy of the reactants, and faster moving reactants will collide more
often. 
Grayce
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The reason is that most reactions have an "activation barrier;" that is, in
the course of the reaction, the reacting molecules need to be in some
arrangement in which the atoms are in specific positions, or the potential
energy of the molecules is higher than before or after the reaction takes
place.  If the activation barrier involves a higher potential energy
(which is usually the case), then increasing the kinetic energy of the
reacting molecules (that is, increasing the temperature - the thermodynamic
definition of temperature is average kinetic energy of the "degrees of
freedom" of the system) will help them to surmount the energy barrier.
This increases the reaction rate.  If the activation barrier only involves
a restricted geometry of the reactants, increasing the temperature will
also increase the rate of the reaction (though it very well may increase
the rate of the reverse reaction even more) by simply making the moelcules
move and vibrate and rotate faster, putting them into the necessary
arrangement more frequently.



 Richard Barrans Jr., Ph.D.
Chemistry Division CHM/200
9700 South Cass Avenue
Argonne, IL 60439
richb@anl.gov
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