How will the temperature of an ideal gas change in an adiabatic expansion?

Explanation

In an adiabatic process, Q = 0
For the expansion of a gas, W is positive .
`:. Q = (U_(f)-U_(i)) + W`
or, `0 = (U_(f) - U_(i)) + W`
or, `U_(f) - U_(i) = -W`
So, `U_(f) < U_(i)`, i.e., internal energy decreases. As the internal energy of a gas depends only on its temperature, the temperature decreases.