"Chemistry" was developed during soundchecks on the "Moving Pictures" tour in 1981. It was during one particular session during the United States leg whereby, after each member checking each of their instruments separately, "a little spontaneous creation" came about which produced a song without the group realising it. Each member played a different part; Lee played what became the keyboard section for the bridge, Lifeson the guitar riffs heard in the verses, and Peart the drum pattern for the chorus. Upon listening to the soundcheck tapes, Lifeson and Lee took each section and arranged it into a complete track before they produced a demo which almost matched the version recorded for the album. "Chemistry" marked the first time that each member collaborated on the lyrics to a song, with Lifeson and Lee devising its title, concept, and several phrases that they wished for it to include. Peart then took their ideas and developed a set of complete lyrics. He named "Chemistry" as the easiest song to write for "Signals".