Question

during an adiabatic process in a closed system, what happens to a gas when the gas expands? its temperature increases. its temperature decreases. its molecules gain mass. its molecules lose mass.

Explanation:

In an adiabatic expansion in a closed - system, the gas does work on the surroundings. Since there is no heat transfer (adiabatic process, $Q = 0$), according to the first law of thermodynamics $\Delta U=Q - W$, the internal energy of the gas ($\Delta U$) decreases as work ($W>0$) is done. For an ideal gas, internal energy is directly related to temperature. So, a decrease in internal energy leads to a decrease in temperature.

Answer:

Its temperature decreases.