Thermodynamics and Thermochemistry - Result Question 76
####1. An ideal gas is allowed to expand from $1 L$ to $10 L$ against a constant external pressure of 1 bar. The work done in $kJ$ is
(2019 Main, 12 April I)
(a) -9.0
(b) +10.0
(c) -0.9
(d) -2.0
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Solution:
- Key Idea Work done during isothermal expansion of an ideal gas is given by the equation.
$$ W=-p _{\text {ext }}\left(V _2-V _1\right) $$
According to the given conditions, the expansion is against constant external pressure. So, the work done is given by following formula;
$$ \begin{aligned} W & =-p _{\text {ext }}\left(V _2-V _1\right) \ & =-1 \text { bar }(10 L-1 L)=-9 L \text { bar } \quad(\because 1 Lbar=100 J) \ & =-9 \times 100 J=-0.9 kJ \end{aligned} $$
