What is an ideal gas?

In a thermodynamic system,the working substance is an ideal gas. Its internal energy is in the form of

Kinetic theory of gases was put forward by

What should be the shape of the container used to find the pressure of an ideal gas?

Modern vacuum pumps can evacuate a vessel down to a pressure of $4.0 \times 10^{-15} \, atm$ at room temperature $(300 \, K)$. Taking $R = 8.0 \, J \cdot K^{-1} \cdot mol^{-1}$,$1 \, atm = 10^5 \, Pa$,and $N_A = 6 \times 10^{23} \, mol^{-1}$,the mean distance between molecules of gas in an evacuated vessel will be of the order of:

$A$ gas in an airtight container is heated from $25^{\circ}C$ to $90^{\circ}C$. The density of the gas will