Thermodynamics and Thermochemistry 1 Question 4
4. During compression of a spring the work done is $10 \mathrm{~kJ}$ and 2 $\mathrm{kJ}$ escaped to the surroundings as heat. The change in internal energy, $\Delta U$ (in $\mathrm{kJ}$ ) is
(2019 Main, 9 April II)
(a) 8
(b) -12
(c) 12
(d) -8
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Solution:
- In the given system, during the compression of a spring the workdone is $10 \mathrm{~kJ}$ and $2 \mathrm{~kJ}$ of heat is escaped to the surroundings. So, $q=-2 \mathrm{~kJ}$ and $W=10 \mathrm{~kJ}$
According to the first law of thermodynamics,
$$ \begin{aligned} & \Delta U=q+W=-2 \mathrm{~kJ}+10 \mathrm{~kJ} \ & \Delta U=8 \mathrm{~kJ} \end{aligned} $$
The change in internal energy, $\Delta U$ (in $\mathrm{kJ}$ ) is $8 \mathrm{~kJ}$.
