Question

Three moles of an ideal gas are compressed isothermally from 60 L to 20 L using constant pressure of 5 atm. Heat exchange Q for the compression is – ____ Lit. atm.

Answer 1

Correct Answer: 200

As isothermal \( U = 0 \) and the process is irreversible:
\[Q = -W = -\left[-P_{\text{ext}}(V_2 - V_1)\right]\]
\[Q = 5 \times (20 - 60) = -200 \, \text{atm-L}\]
Given:
\[P_{\text{ext}} = 5 \, \text{atm}, \quad V_1 = 60 \, \text{L}, \quad V_2 = 20 \, \text{L}\]
Substituting the values:
\[Q = 5 \times (20 - 60) = -200 \, \text{atm-L}\]
Thus, the heat exchange for the compression is \( 200 \, \text{Lit. atm} \).