What is the difference between the heat (q) of a reaction and the reaction enthalpy (Hrxn)?

The heat (q) of a reaction is the amount of energy transferred as heat during a chemical reaction, while the reaction enthalpy (Hrxn) is the overall change in heat energy of a reaction at constant pressure. The main difference is that heat (q) is the actual energy transferred, while reaction enthalpy (Hrxn) is a measure of the total heat change in a reaction.