Question

Based on their activation energies and energy changes and assuming that all collision factors are the same, which of the following reactions would be fastest? (A) Ea = 57 kJ/mol , ΔE = 13 kJ/mol (B) Ea = 47 kJ/mol , ΔE = -29 kJ/mol (C) Ea = 34 kJ/mol , ΔE = -10 kJ/mol .

Answer 1

C is the fastest reaction.

Step-by-step explanation:

Let us consider a generic reaction aA ⇄ bB.

The reaction rate would be:

`r=k.[A]^(n)` [1]

where,

r is the reaction rate

k is the rate constant

n is the reaction order

So we can see that the reaction rate depends on the rate constant. We can find out this constant using the Arrhenius equation:

`k=A.e^(-Ea/R.T)` [2]

where,

A is the collision factor

R is the universal gas constant

T is the absolute temperature

If A and T are the same for different reactions, k will only depend on Ea. According to [2], the lower Ea, the higher the k. According to [1], the higher the k, the higher the r. And when r is higher the reaction is faster. All in all, C has the lowest Ea (34 kJ/mol), so it is the fastest reaction.