State the meaning of the internal energy of a system.
An ideal gas goes through a cycle of changes as shown in Fig. 2.1. At point $P$, the gas has volume $950\,\text{cm}^3$, pressure $2.10 \times 10^5\,\text{Pa}$ and temperature $280\,\text{K}$. The gas is heated at constant volume, and $97.0\,\text{J}$ of thermal energy is transferred to it. Its pressure and temperature alter so that the gas reaches point $Q$ on Fig. 2.1. The gas then undergoes the change from point $Q$ to point $R$ and then from point $R$ back to point $P$, as shown on Fig. 2.1.
State the overall change in internal energy of the gas in the full cycle $P Q R P$. Justify your answer.
On Fig. 2.2, fill in the energy changes for the gas during the change $P \rightarrow Q$.
On Fig. 2.2, fill in the energy changes for the gas during the change $Q \rightarrow R$.
On Fig. 2.2, fill in the energy changes for the gas during the change $R \rightarrow P$.
State the overall change in internal energy of the gas during the complete cycle PQRP. Explain your answer.
On Fig. 2.2, fill in the energy changes for the gas during (1) the change P $\rightarrow$ Q, (2) the change Q $\rightarrow$ R, (3) the change R $\rightarrow$ P.