How is enthalpy used to predict whether a reaction is endothermic or exothermic?

If the enthalpy change is negative, then the reaction is exothermic because heat energy was lost to the surroundings.

If the enthalpy change was positive, then the reaction was endothermic because heat energy was gained from the surroundings!

Hope this helps!! x

A) the enthralling of formation for pure element in its standard state is always positivehope this : )