In: Chemistry
The activation energy for a particular reaction is 84 kJ/mol. By what factor will the rate constant increase when the temperature is increased from 50 oC to 72 oC?
According to Arrhenius Equation , K = A e -Ea / RT
Where
K = rate constant
T = temperature
R = gas constant = 8.314 J/mol-K
Ea = activation energy
A = Frequency factor (constant)
Rate constant, K = A e - Ea / RT
log K = log A - ( Ea / 2.303RT ) ---(1)
If we take rate constants at two different temperatures, then
log K = log A - ( Ea / 2.303RT ) --- (2)
& log K' = log A - (Ea / 2.303RT’) ---- (3)
Eq (3 ) - Eq ( 2 ) gives
log ( K' / K ) = ( Ea / 2.303 R ) x [ ( 1/ T ) - ( 1 / T' ) ]
Given T = 50oC = 50+273 = 323 K
T' = 72 oC = 72+273 = 345 K
Ea = 84 kJ /mol = 84000 J/mol
Plug the values we get
log ( K' / K ) = (84000 / (2.303x8.314) ) x [ ( 1/ 323 ) - ( 1 /345 ) ]
= 0.866
K'/K = 100.866
= 7.35
K' = 7.35 x K
Therefore the required factor is 7.35