How does a gas change its internal energy when it absorbs heat and does work?

According to the first law of thermodynamics, the change in the internal energy ($\Delta U$) of a gas is determined by the balance between the heat absorbed by the system and the work performed by it.12

When a gas absorbs heat ($Q$) from its surroundings and does work ($W$) on its surroundings, the change in its internal energy is expressed by the equation:

$$\Delta U=Q-W$$

In this relationship, the internal energy acts as a state function, meaning its change depends only on the initial and final states of the system. Conversely, heat and work are not state functions; their values depend on the specific path or process taken to reach the final state. Essentially, the first law functions as a strict energy accounting system where the change in internal energy represents the net result of energy "deposits" (heat added to the gas) and "withdrawals" (work done by the gas).132