Some energy values associated with a chemical reaction are shown in the table - Scottish Highers Chemistry - Question 21 - 2022

To determine the correct potential energy diagram, we need to analyze the given data:

• The enthalpy of the reactants is 30 kJ mol⁻¹.
• The activation energy for the forward reaction is 110 kJ mol⁻¹, which indicates that the potential energy of the products must be higher than that of the reactants (30 kJ mol⁻¹ plus the activation energy).
• For the reverse reaction, the activation energy is 70 kJ mol⁻¹, meaning that the products have a lower potential energy compared to the transition state but higher relative to the enthalpy of reactants.

Considering these factors:

• The energy of the products must therefore be about 30 + 110 = 140 kJ mol⁻¹ at the peak of the transition state and decrease to a stable value (which is lower due to reverse reaction activation energy) after the activation energy is overcome.

Thus, the only diagram that reflects this scenario correctly is option D.