To understand better the impact of gas phase reactions on chemical vapor deposition, a new experimental method has been developed to isolate and study homogeneous reactions separately from heterogeneous reactions. This new system heats reactant gases by rapidly compressing them to temperatures greater than 1,000 K; the walls of the reactor remain constant at 500 K or less. Pressure and volume measurements determine the mean temperature of the gas. Results from a series of test reactions and simple models show that this apparatus and measurement method work well. The apparatus is inexpensive and simple to use, and has advantages over shock tubes and static systems.