In a reaction energy diagram, which part of the diagram represents the change in enthalpy (ΔH) for the reaction?

• A. The area under the curve
• B. The peak of the curve above the reactants
• C. The vertical distance between the reactants and products
• D. The horizontal distance from reactants to products

Answer: (C)

Verified step by step guidance

1. Understand that a reaction energy diagram plots the potential energy of the system as the reaction progresses from reactants to products.
2. Identify that the change in enthalpy (\$\Delta H\$) corresponds to the difference in energy between the reactants and the products, not the energy barrier or the area under the curve.
3. Recognize that the peak of the curve above the reactants represents the activation energy, which is the energy required to reach the transition state, not \$\Delta H\$.
4. Note that the horizontal distance from reactants to products represents the progress of the reaction over time or reaction coordinate, which is unrelated to enthalpy change.
5. Conclude that the vertical distance between the energy level of the reactants and the energy level of the products on the diagram represents the enthalpy change \$\Delta H = E_{products} - E_{reactants}\$.