Temperature Increase: As temperature increases, rate increases and the value of rate constant k
increases. This is due to two factors…
Kinetic Energy: As temperature increases, particles move faster and collide more frequently.
Activation Energy: Increasing temperature shifts Boltzmann distribution to right, increasing
proportion of particles that exceed activation energy Ea. Change in rate mainly determined by Ea.
Arrhenius Equation: This the exponential form of equation.
k = Ae-Ea/ RT
R = gas constant = 8.314 J mol-1 K-1
. T in Kelvin.
e
-Ea/ RT
, Exponential Factor: The exponential factor represents proportion of molecules that
exceed Ea for reaction to take place.
A, Pre- Exponential Factor: Pre- exponential factor or frequency factor is the frequency of
collisions with correct orientation. A is a constant giving the rate if no activation energy.
Logarithmic Form of Arrhenius Equation: ln k = –
Ea
RT
+ lnA.
Gives negative gradient straight line graph. Y = mx + c.
1
T
= x
–
Ea
R
= gradient = dy/ dx. lnA = y intercept. Put ln k on y axis and 1/ T on x axis.
Sub T into 1/T and k into lnk.
Pick two points to work out gradient and use this to work out activation energy by multiplying by
R, 8.314. May need to divide by something else such as 10-3 depending on units.
If need extend graph to find y intercept. lnA = 25 use inverse e25 = A.
If axis does not start at 0, cannot always extend line of best fit to find y intercept or other points
outside range of data. Instead once know gradient of line, substitute in values to find unknown
ln A.
