rate determining step and arrhenius eqn

what is the rate determining step?

• slowest step of a reaction mechanism

• determines overall rate

how can we use evidence from the rate equation to explain why a step is the RDS:

• species [X] (or more) is in the rate equation and in step 1

• so step 1 must be the RDS 

rate = k[B]²[H⁺]

• step 2

• by the end of step 2, 1x H⁺ and 2x B have been used (as seen in the rate eqn)

what does the Arrhenius eqn show?

shows the effects of changing the temp/E_a of the reaction on the rate constant

give the standard form of the Arrhenius eqn and explain what each of the values represent:

give the logarithmic form of the Arrhenius eqn and explain what each of the values represent: 

how does E_a affect the rate constant?

• as E_a increases, k decreases

• as the higher the E_a, the fewer reactant particles will have sufficient E to react

• so fewer successful collisions occur

• this means a reaction w/ high E_a has a lower RoR

how does temperature affect the rate constant (k)?

• temp increase → exponential increase in k

• E_K of particles increases and particles move faster

• so a higher proportion of particles have an energy at/above the E_A

• so there is a higher frequency of successful collisions

• so RoR increases

explain why increasing temp has a much greater effect on RoR than increasing [E]:

• reaction occurs when molecules have E ≥ E_a

• increase temp causes many more molecules to have this E (sig higher fraction of molecules have Es ≥ E_a)

• so higher prop of collisions become successful and RoR increases more

• whereas increasing [E] only increases no. w/ this E