There are a few ways to determine the effect of heat on a reaction. One way is to measure the temperature change of the reaction mixture. If the temperature increases, then the reaction is exothermic, meaning that it releases heat. If the temperature decreases, then the reaction is endothermic, meaning that it absorbs heat.

Another way to determine the effect of heat on a reaction is to observe the reaction rate. If the reaction rate increases with increasing temperature, then the reaction is exothermic. If the reaction rate decreases with increasing temperature, then the reaction is endothermic.

Finally, the effect of heat on a reaction can also be determined by measuring the equilibrium constant. The equilibrium constant is a measure of the extent to which a reaction proceeds in the forward direction. If the equilibrium constant increases with increasing temperature, then the reaction is exothermic. If the equilibrium constant decreases with increasing temperature, then the reaction is endothermic.

By measuring the temperature change, reaction rate, or equilibrium constant, it is possible to determine the effect of heat on a reaction.