One of these systems consisting entirely of photons enclosed in a perfectly absorptive container is a model for blackbody radiation. One basic model of these things describes pressure as arising from elastic collisions with their containers. A more-sophisticated law describing these things accounts for compressibility and intermolecular forces using "a" and "b" parameters, and was developed by van der Waals. A constant named for these things is about 8.31 in SI units and
One of these systems consisting entirely of photons enclosed in a perfectly absorptive container is a model for blackbody radiation. One basic model of these things describes pressure as arising from elastic collisions with their containers. A more-sophisticated law describing these things accounts for compressibility and intermolecular forces using "a" and "b" parameters, and was developed by van der Waals. A constant named for these things is about 8.31 in SI units and is denoted by the letter "R". For 10 points, name these gases which are described by their namesake law, which reads "P V equals n R T". 
One of these systems consisting entirely of photons enclosed in a perfectly absorptive container is a model for blackbody radiation.
ideal gases [accept ideal after "gases" is read; prompt on "gas" or word forms] 