Physics 9702 · AS & A Level · The first law of thermodynamics
The first law of thermodynamics — practice question
A fixed mass of ideal gas has a volume of $3.49 \times 10^3\,\text{cm}^3$ at a temperature of $21.0^\circ\text{C}$. After heating, $565\,\text{J}$ of thermal energy makes it expand to a volume of $3.87 \times 10^3\,\text{cm}^3$ at $53.0^\circ\text{C}$. Fig. 2.1 shows this.
(a)[2]
Show that the gas has the same pressure initially and finally.
(b(i))[2]
The gas pressure is $4.20 \times 10^5\,\text{Pa}$. For this heating process, calculate the work done by the gas.
(b(ii))[2]
Use the first law of thermodynamics and your answer in (i) to find the change in internal energy of the gas.
(c)[3]
Explain why the change in kinetic energy of the molecules of this ideal gas is equal to the change in internal energy.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Temperatures are converted into kelvin” …