The discussions about “Thermal effect of chemical reactions” is elaborately described in this paper. The increase of the rate of reaction due to the presence of heat is discussed below. The produced and required heats for the chemical reaction are referred to be in this topic. Two different thermochemical reaction and their comparison is mentioned in this paper. The effects of temperature, the methodology, ethical issues and hazards followed by the heat reactors are well discussed in this topic. Few recommendations to avoid the risk associated have been described here.