The discussion clarifies the distinction between 'q' (heat transfer) and 'ΔH' (change in enthalpy) in thermochemistry. 'q' specifically refers to the amount of heat transferred, while 'ΔH' encompasses the total energy change in a system, including heat, pressure/volume work, and entropy. For ΔH to equal q, conditions must be met where there is no change in pressure or volume and entropy is neglected. Additionally, the relationship between Gibbs' free energy (ΔG) and these terms is highlighted, with ΔG representing the useful energy change of the system under constant temperature and pressure, calculated as ΔH minus entropy.