Question

Calculate the change in internal energy (ΔE) for a system that is giving off 25.0 kJ of heat and is changing from 12.00 L to 6.00 L in volume at 1.50 atm pressure. (Remember that 101.3 J = 1 L • atm)

Answer 1

Changein volume, \(\Delta \mathrm{V}=12-6=6 \mathrm{~L}\)

\(\mathrm{q}=-25.0 \mathrm{KJ}(\) negative sign because heatis given out of the system \()\)

$$ \begin{array}{l} \text { pressure, } \mathrm{P}=1.5 \text { 0atm } \\ \mathrm{P} \Delta \mathrm{V}=1.50 \mathrm{~atm} \times 6 \mathrm{~L} \\ =9 \mathrm{Latm} \\ =9 \times 101.3 \\ =911.7 \mathrm{~J} \\ \Delta \mathrm{E}=\mathrm{q}+\mathrm{w}(\text { work done will be positive asitis a compression }) \\ \Delta \mathrm{E}=\mathrm{q}+\mathrm{P} \Delta \mathrm{V} \\ =-25000 \mathrm{~J}+911.7 \mathrm{~J} \\ =-24088.3 \mathrm{~J} \\ =-24.1 \mathrm{KJ} \end{array} $$