Question

energy diagram
energy
reaction progress
what does line e represent?
activation energy (forward)
energy of the reactants
enthalpy of reaction
energy of the products

Explanation:

In a chemical energy diagram, the enthalpy of reaction ($\Delta H$) is the difference in energy between the products and reactants. The line E here shows the vertical difference between the energy level of reactants (initial) and products (final). Activation energy is the energy needed to reach the transition state, energy of reactants is the initial level, energy of products is the final level. So E represents the enthalpy of reaction (energy change of the reaction).

Answer:

enthalpy of reaction