Question

An ideal gas initially at $30K$ undergoes an isobaric expansion of $2.50kPa$. If the volume increases from $1.00m^3$ to $3.00m^3$ and $12.5kJ$ is transferred to the gas by heat, what is the change in its internal energy (in joules)?

Answer 1

The gas pressure is much less than one atmosphere. This could be managed by having the gas in a cylinder with a piston on the bottom end, supporting a constant load that hangs from the piston. The (large) cylinder is put into a warmer environment to make the gas expand.
The first law of thermodynamics will tell us the change in internal energy. The ideal gas law will tells us the final temperature.
1. $\Delta U=Q+W$
where $W=-P\Delta V$ for a constant pressure process.
So $\Delta U=Q-P\Delta V$
$\Delta U=1.25\times {10}^{4}J-(2.50\times {10}^{3}N/m^2)\times (3.00m^3\times 1.00m^3)=7500J$