Q4. Two identical containers each hold the same ideal gas at 300 K and 1.0 × 10 Pa. They are joined so that the gas fills both. Which of these change: total volume, total amount, pressure, temperature, density?
Compared with one original container, the combined volume and amount are doubled; the totals for the two-container system were already that large before opening the connection. Pressure, temperature and density stay the same (intensive), since the combined gas is just two copies of the same state side by side.
Q5. What is an isotherm? Sketch how two isotherms of the same ideal gas at different temperatures compare.
An isotherm is the curve of pressure against volume at a fixed temperature; for an ideal gas, PV = constant, a hyperbola. The isotherm at the higher temperature has a larger constant μRT (same μ), so it lies further from both axes.
Q6. Is the petrol–air mixture in an engine cylinder in an equilibrium state while it explodes? Why or why not?
No. During the explosion the temperature and pressure vary from place to place in the cylinder, so the gas is not in an equilibrium state and cannot be described by single values of P and T. After it settles, a single equilibrium pressure and temperature can describe it again.