In the collision model it is assumed that reactions occur as a result of collisi
ID: 701374 • Letter: I
Question
In the collision model it is assumed that reactions occur as a result of collisions between molecules with the correct kinetic energy and orientation. The minimum energy required for a reaction to occur when molecules collide is called the activation energy, Ea. The number of collisions that are favorably oriented for a reaction is described by the frequency factor, A. The Arrhenius equation relates both of these factors to the rate constant, k:
k=AeEa/(RT)
where R=8.314 J/(molK) and T is the temperature in kelvins.
1. Part B
A certain reaction with an activation energy of 145 kJ/molkJ/mol was run at 465 K and again at 485 K . What is the ratio of f at the higher temperature to f at the lower temperature?
Express your answer numerically using one significant figure.
Explanation / Answer
Arrhenius equation
k=Aexp(-Ea/RT)
For higher temperature T1 = 485 K
k1=Aexp(-Ea/RT1)
For lower temperature T2 = 465 K
k2=Aexp(-Ea/RT2)
Divide both equations we get
k1 /k2 = exp [-(Ea/R) (1/T1 - 1/T2)]
= exp [-(145*1000/8.314) (1/485 - 1/465)]
= exp (-1.5466)
k1/k2 = 0.2129 = 0.2