Question

Draw a rough sketch of the energy profile for each of the following cases.

$$\begin{gathered} a.𝛥E=+10kJ/mol,Ea=25kJ/mol \\ b.𝛥E=-10kJ/mol,Ea=50kJ/mol \\ c.𝛥E=-50kJ/mol,Ea=50kJ/mol \end{gathered}$$

Which reaction will have the greatest rate at 298 K? Assume the frequency factor A is the same for all three reactions.

Short answer

The energy profile (energy vs. reaction progress) diagram is shown below. At 298K, the reaction with E_a = 25 kJ/mol will have the greatest rate.

Step-by-step solution

Drawing the energy profile at Ea = 25 kJ/mol and 𝛥E = 10kJ/mol

In the above fig, 𝝙E is positive that the heat is absorbed. Thus, the reaction is endothermic.

Drawing the energy profile at Ea = 50 kJ/mol and 𝛥E = -10kJ/mol

In the above fig, 𝝙E is negative the heat is released. Thus, the reaction is exothermic.

Drawing the energy profile at Ea = 50 kJ/mol and 𝛥E = -50kJ/mol

In the above fig, 𝝙E is negative, the heat is released. Thus, the reaction is exothermic.

Describe the greatest rate of reaction from the above diagrams.

The reaction with the activation energyE_a = 25 kJ/mol will have the greatest rate. Because as the activation energy increases, the rate constant decreases according to the Arrhenius equation.