Final answer:
Enthalpy changes are positive for endothermic processes that absorb heat and negative for exothermic processes that release heat, corresponding to the direction of heat flow.
Step-by-step explanation:
In chemistry, enthalpy changes are defined as being positive for endothermic processes and negative for exothermic processes. An endothermic process is a chemical reaction or physical change that absorbs heat, resulting in an increase in the system's enthalpy (ΔH) as heat is taken in from the surroundings, which makes the value of ΔH positive. Conversely, an exothermic process is one where heat is released into the surroundings, leading to a decrease in system's enthalpy, making the value of ΔH negative. The quantity of heat for a process is represented by the letter 'q', and the sign of 'q' is positive for endothermic processes and negative for exothermic ones, reflecting the direction of heat flow.