How is the energy change (ΔH) in a chemical reaction measured?

In a chemical reaction, the change in enthalpy (ΔH) reflects the difference in energy content between the products and the reactants. When a reaction occurs, energy is either absorbed or released depending on whether the products have a higher or lower energy level compared to the reactants.

This energy change is quantified by taking the total energy of the products and subtracting the total energy of the reactants. If the resulting value is negative, it indicates an exothermic reaction, where energy is released; if positive, it denotes an endothermic reaction, where energy is absorbed. Thus, measuring ΔH by evaluating this energy difference provides crucial insight into the thermodynamic behavior of a chemical process, explaining why this option effectively defines the measurement of energy change.

In contrast, calculating weight differences, observing gas production rates, or averaging energies of all particles does not accurately capture the fundamental thermodynamic changes occurring throughout a chemical reaction. These activities may provide useful data but do not directly measure the enthalpic changes that define the energy dynamics of the reaction.