According to the First Law of Thermodynamics, energy change is equal to which of the following?

The First Law of Thermodynamics states that the change in the internal energy of a system is equal to the heat added to the system minus the work done by the system on its surroundings. This relationship can be expressed mathematically as:

ΔU = Q - W

Where:

• ΔU is the change in internal energy.
• Q is the heat flow into the system.
• W is the work done by the system.

Since the question asks for the relationship involving heat flow into the system and work done, understanding the internal energy context is crucial. When we rearrange the formula, if we want to consider the work done on the system instead of work done by the system, we express it as:

ΔU = Q + W' (where W' is the work done on the system), which accounts for positive work input into the system.

This means that if work is done on the system, we should add that energy to the system's internal energy, alongside any heat added. Therefore, the correct understanding aligns with option B, which correctly reflects that the change in internal energy corresponds to the heat added plus the work done on the system. This framework helps solidify the concept of energy conservation and transformation within a thermodynamic system.