Реферат: Rates Of Reaction Essay Research Paper Rates

small input of energy to start their exceedingly exothermic reactions.

In gases the energy of the particles is mainly kinetic, however in a solid of a

given mass this amount of energy is determined by their velocities.

This graph below shows how the energies of particles are distributed.

This graph is basically a histogram showing the number of particles with that

amount of energy. The area underneath the curve is proportional to the total

number of particles. The number of particles with > EA is proportional to the

total area underneath the curve.

The fraction of particles with > EA is given by the ratio:

Crosshatched area under the curve

total area under curve

Using the probability theory and the kinetic theory of gases, equations were

derived for the distribution of kinetic energy amongst particles. From these

equations the fractions of particles with an energy > EA J mole-1 is represented

by the equation: e -Ea/RT where R= the gas constant (8.3 J K-1 mole -1)

T= absolute temperature.

This suggests that at a given temperature, T,

The reaction rate ? e -Ea/RT

If we use k as the rate constant, as a measure of the reaction rate we can put

this into the equation also.

k? e -Ea/RT

? k= A e -Ea/RT

The last expression is called the Arrhenius equation because it was developed

by Srante Arrhenius in 1889. In this equation A can be determined by the total

numbers of collisions per unit time and the orientation of the molecules when

the collide, whilst e -Ea/RT is determined by the fraction of molecules with

sufficient amounts of energy to react.

Putting the probability theory and the kinetic theory together this now gives

us a statement which accounts for the 100% increase in the rate of reaction in a