Question

An ideal gas undergoes an adiabatic expansion, a process in which no heat flows into or out of the gas. As a result,

(a) the temperature of the gas remains constant and the pressure decreases.

(b) both the temperature and pressure of the gas decrease.

(c) the temperature of the gas decreases and the pressure increases.

(d) both the temperature and volume of the gas increase.

(e) both the temperature and pressure of the gas increase

Short answer

The correct option is (b).

Step-by-step solution

Concepts 

From the first law of thermodynamics, you get $\mathrm{\Delta }U=Q-W$.

Now, for the adiabatic process,$Q=0$.

Explanation 

Now, for the adiabatic process, you get:

$\begin{array}{c}\mathrm{\Delta }U=Q-W\\ \mathrm{\Delta }U=-W\end{array}$

For adiabatic expansion, the distance between the gas molecules increases, which causes a decrease in pressure.

In adiabatic expansion, the work is done by the gas; so the internal energy of the gas decreases, which results in a decrease in temperature.

Hence, option (b) is the correct answer.