Thermodynamics Question 1

Question 1 - 24 January - Shift 1

$1 g$ of a liquid is converted to vapour at $3 \times 10^{5} Pa$ pressure. If $10 \%$ of the heat supplied is used for increasing the volume by $1600 cm^{3}$ during this phase change, then the increase in internal energy in the process will be :

(1) $4320 J$

(2) $432000 J$

(3) $4800 J$

(4) $4.32 \times 10^{8} J$

Show Answer

Answer: (1)

Solution:

Formula: Work done in isobaric process

Work done $=P \Delta V$

$ \begin{aligned} & =3 \times 10^{5} \times 1600 \times 10^{-6} \\ & =480 J \end{aligned} $

Only $10 \%$ of heat is used in work done.

Hence $\Delta Q=4800 J$

The rest goes in internal energy, which is $90 \%$ of heat.

Change in internal energy $=0.9 \times 4800=4320 J$