Final answer:
The missing term in the equation ΔE = q + blank, for the internal energy change of a system, is 'work', represented by the letter 'w'. This relationship is a manifestation of the first law of thermodynamics.
Step-by-step explanation:
The internal energy of a system can be changed by a flow of work, heat, or both. That is, ΔE = q + w, where delta E represents the change in the system's internal energy, q represents heat, and w represents work. The correct fill-in-the-blank for your equation is D) Work. This is one version of the first law of thermodynamics, which states that the internal energy of a system changes through heat flow into or out of the system (positive q is heat flow in; negative q is heat flow out) or work done on or by the system (positive w is work done on the system, negative w is work done by the system). For example, if heat is added to a system or work is performed on it, its internal energy increases (positive ΔU). Conversely, if heat is removed from the system or it does work by pushing back the surroundings, its internal energy decreases (negative ΔU).