Ideal Gas Lab
Experimental apparatus
Movable piston, with absolute pressure and temperature.
Concept figure · Constant-temperature process
For a fixed amount of ideal gas at constant temperature, pressure decreases as volume increases.
Experiment
Live p–V diagram
Solid line: current isotherm. Dashed line: reference isotherm.
First-law energy balance
JC convention: W is work done ON the gas. ΔU = Q + W.
Adjust the apparatus, then Check.
The physics
Ideal gas: pV = nRT, where p is absolute pressure (Pa), V is volume (m³), n is amount (mol), T is absolute temperature (K), and R = 8.31 J K⁻¹ mol⁻¹.
Conversions: 1 kPa = 1,000 Pa; 1 cm³ = 10⁻⁶ m³; 1 L = 10⁻³ m³; T(K) = θ(°C) + 273.
Kinetic theory: pV = ⅓Nm⟨c²⟩ and cᵣₘₛ = √(3kT/m).
Mean translational kinetic energy: ⟨Eₖ⟩ = 3kT/2, where k = 1.38 × 10⁻²³ J K⁻¹.
Avogadro constant: N_A = 6.02 × 10²³ mol⁻¹.
First law: ΔU = Q + W; W is work done ON the gas. At constant volume, W = 0. At constant pressure, W = −p(V₂ − V₁). Positive Q is heat supplied to the gas.
Assumptions: ideal gas with negligible intermolecular forces, thermal equilibrium, quasi-static constant-pressure processes where used, and no heat lost to the container.