Q16.62P - Chemistry: Molecular Nature Of Matter And Change

Question

For the reaction , $\mathbf{A}\mathbf{B}\mathbf{C}\mathbf{+}\mathbf{D}\mathbf{\rightleftharpoons }\mathbf{A}\mathbf{B}\mathbf{+}\mathbf{C}\mathbf{D}$, $\mathbf{∆}{{\mathbf{H}}^{\mathbf{0}}}_{\mathbf{r}\mathbf{\times }\mathbf{n}}\mathbf{=}\mathbf{ }\mathbf{ }\mathbf{-}\mathbf{ }\mathbf{55}\mathit{k}\mathit{J}\mathbf{/}\mathit{m}\mathit{o}\mathit{l}$ ${\mathit{E}}_{\mathbf{a}\left(fwd\right)}\mathbf{=}\mathbf{215}\mathit{k}\mathit{J}\mathbf{/}\mathit{m}\mathit{o}\mathit{l}$ Assuming a one-step reaction,

(a) Draw a reaction energy diagram;

 (b) Calculate Ea(rev); and 

(c) Sketch a possible transition state if ABC is V-shaped

Step-by-Step Solution

Answer

1. The reaction energy diagram is 

b. The $E_{a\left(rev\right)}$  is equal to 270 kJ/mol.

c. A transition occurs when an old bond (B-C) weakens and a new bond forms 

(C-D). Sketch the reaction's transition stage as follows:

Step 1: Draw a reaction energy diagram

It's an exothermic process. As a result, the energy of products will be smaller than that of reactants. The reaction's energy diagram will look like this:

Step 2: Calculation of Ea ( rev )

Determine the $E_{a\left(rev\right)}$  as follows:

Here $E_{a\left(rev\right)}$ is the activation energy of the reverse reaction.

$E_{a\left(fwd\right)}$  is the activation energy of the forward reaction and $∆H_{r\times n}$ is the change in enthalpy of the reaction.

$$\begin{gathered} E_{a\left(rev\right)}=E_{a\left(fwd\right)}-∆H_{r\times n} \\ =215kJ/mol-\left(-55kJ/mol\right) \\ =270kJ/mol \end{gathered}$$ 

Thus, the $E_{a\left(rev\right)}$  is equal to 270 kJ/mol.

Step 3: Sketch a possible transition state

A transition occurs when an old bond (B-C) weakens and a new bond forms (C-D). Sketch the reaction's transition stage as follows: