A reaction is represented on an energy diagram described as follows.
• The energy of the reactants is defined as the zero of the vertical axis.
• The curve rises smoothly to a maximum of 65 kJ before descending directly to the products, which are located at –25 kJ on the same vertical scale.
No plateaus or additional maxima are observed between reactants and products.
Use this verbal description to analyze the thermodynamic features of the process.
(a) Describe whether the reaction is exothermic or endothermic and cite specific numerical evidence from the diagram to support your conclusion.
(b) Identify the numerical value of the enthalpy change, ΔHrxn, for the reaction. Explain how you determined both its magnitude and sign without performing any arithmetic beyond simple subtraction.
(c) Explain why no intermediates are present in this reaction mechanism, making explicit reference to key features of the energy profile.
(d) Discuss how the position of the transition state relative to reactants and products provides insight into the relative magnitudes of the forward and reverse activation energies, even though the reverse activation energy is not explicitly graphed.