In November 2154, tampering by a group of Klingons caused a malfunction in the intermix chamber aboard Enterprise NX-01. As a result, plasma pressure within the chamber began to rise, threatening to destroy the ship. In order to reduce the pressure, Enterprise had to maintain high warp until the damage could be repaired. (ENT: "Affliction")
In 2266, as the USS Enterprise made an attempt at breaking free of an alien pilot vessel's tractor beam, the intermix chamber superheated with the coolant temperature rising 2,000 degrees above maximum. (TOS: "The Corbomite Maneuver")
In 2370, while posing as a thief named Galen, Captain Jean-Luc Picard manufactured an intermix chamber malfunction on board Arctus Baran's mercenary vessel, causing the ship to accelerate out of control and the plasma pressure to increase. (TNG: "Gambit, Part I")
In dialogue from the final draft script of TOS: "The Naked Time", Montgomery Scott reported to Captain Kirk that the USS Enterprise's "inter-mix chamber" was "cycling now" and could take "twenty-two or three minutes." The direct reference to the ship's intermix chamber is not in the final version of the episode, though Scott's estimate of approximately twenty-two or -three minutes is.
In Mr. Scott's Guide to the Enterprise, the function of the intermix chamber of a refit Constitution-class is explained in detail. Both matter and antimatter flow simultaneously inside the intermix chamber. The chamber is divided into a vertical and a horizontal chamber that join together in main engineering. The horizontal chamber branches out to the nacelles and also powers all of the phaser banks. The vertical chamber is connected at the upper end to the impulse deflection crystal, that normally powers the impulse drive. At the bottom of the vertical chamber are the matter and antimatter pods from which the reactants are drawn. In the warp cores of tye 23rd century the resulting energy is directed to the dilithium crystal converter matrix to be energized into warp plasma for the warp engines. (TOS: "That Which Survives", "Elaan of Troyius"; Star Trek II: The Wrath of Khan) By the 24th century warp cores were upgraded to combine the MARA and the dilithium crystal assembly into the reaction chamber in one unit. (TNG: "Relics") There are several energy converters connected to the vertical chamber that provide plasma for the more basic ship functions not related to propulsion as well. The Electro Plasma Support (EPS) power grid distributes this plasma throughout the ship to power its systems.