Question

calculate the change in internal energy if a system absorbs 1525 j of heat from its surroundings while expanding a piston from 10.2 l to 28.5 l at a constant pressure of 1.00 atm.
-3380 j
1510 j
329 j
-1510 j
3380 j
-329 j
calculate the change in internal energy if a system releases 857 j of heat to its surroundings while expanding a piston from 5.60 l to 16.50 l at a constant pressure of 0.958 atm.
-847 j
-1915 j
201 j
847 j
-201 j
1915 j

Explanation:

Step1: Calculate work done ($W$)

The formula for work done at constant pressure is $W = -P\Delta V$.
First, find $\Delta V$: $\Delta V=V_{final}-V_{initial}$.
For the first problem: $\Delta V = 28.5 - 10.2=18.3\ L$.
Convert $L\cdot atm$ to $J$: $1\ L\cdot atm = 101.3\ J$.
$W=-P\Delta V=-1.00\times18.3\times101.3=-1853.79\ J$.
Then use the first - law of thermodynamics $\Delta U=Q + W$. Given $Q = 1525\ J$.
$\Delta U=1525-1853.79=-328.79\approx - 329\ J$.

For the second problem: $\Delta V=16.50 - 5.60 = 10.9\ L$.
$W=-P\Delta V=-0.958\times10.9\times101.3$.
$W=-0.958\times1104.17=-1057.7\ J$.
Given $Q=-857\ J$ (since heat is released).
$\Delta U=Q + W=-857-1057.7=-1914.7\approx - 1915\ J$.

Answer:

• For the first question: - 329 J
• For the second question: - 1915 J