Question

An ideal gas is allowed to expand from 1 L to 10 L against a constant external pressure of 1 bar. The work done is [1 bar = 100 J]}

• A. -9.0 kJ
• B. -0.9 kJ
• C. +10.0 kJ
• D. +0.1 kJ
• E. -2.0 kJ

Hint:

For expansion: \[ w=-P_{\text{ext}}\Delta V \] Expansion gives negative work in chemistry sign convention.

Answer 1

The Correct Option is B

Work done in expansion against constant external pressure is: \[ w=-P_{\text{ext}}\Delta V \] Given: \[ V_1=1L,\qquad V_2=10L \] So, \[ \Delta V = 10-1=9L \] External pressure: \[ P_{\text{ext}}=1 \text{ bar} \] Thus, \[ w=-(1)(9)= -9 \text{ L bar} \] Now use: \[ 1 \text{ L bar} = 100 \text{ J} \] So, \[ w=-9\times 100 = -900\text{ J} \] \[ w=-0.9\text{ kJ} \]
Hence, the correct answer is: \[ \boxed{(B)\ -0.9\text{ kJ}} \]