IPA: /θɜːrməʊˈkɛmɪstri/
KK: /θɜrməˈkɛmɪstri/
This is a field of chemistry that studies how heat is involved in chemical reactions and changes in physical states.
Thermochemistry helps scientists understand how much heat is released or absorbed during a reaction.
Thermochemistry is formed from "thermo-" (from Greek "thermos", meaning heat) and "chemistry" (from Greek "khemia", meaning the art of transmuting metals). The word refers to the branch of chemistry that deals with the relationship between heat and chemical reactions.
Think of 'heat' ('thermo-') and how it relates to the 'art of chemistry' ('khemia') — that's what thermochemistry studies.