REAKSIYaHOI KhIMIYaVI, reaksiyahoero guyand, ki dar jarayoni onho yak khel modda ba moddai kheli digar (az jihati tarkib yo sokhti khi- miyavi farqkunanda) tabdil meyobad.
Reaksiyai khimiyavi az tasiri mutaqobili moddaho va yo ba onho tasir namudani omilhoi beruni (harorat, fishor, maydoni magniti, maydoni elektri va gayra) jarayon megirad. Dar rafti Reaksiyai khimiyavi tabdili yak modda (reagent) ba moddai digar (mahsuli reaksiya) dar shakli muodilahoi khimiyavi ifoda meyobad. Ba har yak reaksiya tanosubi stekhiometri (miqdori muayyani moddaho) va surati muayyani jarayongiri khosand. Reaksiyai khimiyavi ba tabiati moddaho va sharoithoi beruna vobasta ast. Qismi ziyodi Reaksiyai khimiyavi faqat az tasiri manbahoi berunii energiya (energiyahoi garmi, elektromagniti va elektri) jarayon megirad. Reaksiyai khimiyaviro az rui alomathoi gunogun tasnif medihand: az rui adadi molekulahoi dar har yak akti elementari ishtirokkunanda (Reaksiyai khimiyavii mono- va bimolekulavi), mekhanizmi kinetiki (paydarham, paralleli va gayra), sirishti prosessi khimiyavi (tajziya, oksidshavi, polimerizatsiya), navhoi zarrahoi dar Reaksiyai khimiyavi ishtirokkunanda (ioni, radikali, molekulavi), holati fazavii sistemai mutaassir (gazi, moei va gayra). Reaksiyai khimiyavii yakjinsa (gomogeni) dar hajmi fazai mazkur, Reaksiyai khimiyavii gayriyakjinsa (geterogeni) dar sathi judoshavii fazaho ba amal meoyand.