Question

Two reactions, $A\to$ Products and $B\to$ Products, have rate constants $k_A$ and $k_B$ at temperature $T$ and activation energies $E_A$ and $E_B$ respectively. If $k_A>k_B$ and $E_A<E_B$ and assuming that collision frequency for both the reactions is same, then:

• A. At higher temperature $k_A$ will be greater than $k_B$
• B. At lower temperature $k_A$ and $k_B$ will be close to each other in magnitude
• C. As temperature rises, $k_A$ and $k_B$ will be close to each other in magnitude
• D. At lower temperature $k_A>k_B$

Answer 1

Answer: (A), (C)

At higher temperature $k_A$ will be greater than $k_B$
As temperature rises, $k_A$ and $k_B$ will be close to each other in magnitude

For both reactions:

$k_A=A_A{e}^{-E_a/RT}{k}_B=A_B{e}^{-E_a^{\prime }/RT}{A}_A=A_B=A$

Since $E_a<E_a^{\prime }$ thus even at higher temperature $k_A>k_B.$

But $k_A$ and $k_B$ will converge at ${lim}_{T\to \infty }$ where $k_A=k_B=A.$