The zeroth law of thermodynamics states that if objects A and B are separately in thermal equilibrium with a third object C, then objects A and B are in thermal equilibrium with each other.
An ideal gas is one for which . An ideal gas is described by the equation of state,
where equals the number of moles of the gas,
p is its pressure,
V is its volume,
R is the universal gas constant (8.314 J/mol · K), and
T is the absolute temperature of the gas.
A real gas behaves approximately as an ideal gas if it has a low density.