Question

In a thermodynamic process the pressure of fixed mass of gas is changed. In this process gas releases 20 J heat and 8 J work is done on the gas. If initial internal enrgy of the gas is 30 J, then final internal energy is:

• A. 2 J
• B. 42 J
• C. 18 J
• D. 58 J

Answer 1

Answer: (C)

18 J

Here the system is closed system and we can use the first law of thermodynamics, According to the first law of thermodynamics,

$\Delta E_{sys}=q+w$

here $\Delta E_{sys}=E_{final}-E_{initial}$

and w= work done on the system and q=heat provided to the system

Given data: $E_{initial}=30J$ and $q=-20J$ and $w=8J$

then from above equation, we get $E_{final}-30J=8J-20J$

hence $E_{final}=18J$