Final answer:
In thermodynamics, work done by a system on the surroundings is considered negative (W is negative), while heat gained by the system from the surroundings is considered positive (Q is positive).
Step-by-step explanation:
The conventions used in thermodynamics for indicating heat and work interactions with a system. When a system does work on its surroundings, the work (W) is considered negative because energy is leaving the system. Conversely, when a system gains heat from the surroundings, the heat (Q) is considered positive as it leads to an increase in the system's internal energy.
Thus, when a system is doing work on the surroundings while simultaneously gaining heat from the surroundings, W would be negative and Q would be positive. This relationship is summarized by the first law of thermodynamics, often written as ΔU = Q - W, where ΔU is the change in internal energy, Q is the net heat added to the system, and W is the total work done by the system.