ΔH represents the change in enthalpy, specifically the difference between the enthalpy of products and reactants for a reaction. It indicates whether heat is released (-ΔH) or absorbed (+ΔH).
A chemical reaction where heat is released to the surroundings. (-ΔH)
A chemical reaction where heat is absorbed from the surroundings. (+ΔH)
Thermochemistry: The branch of chemistry that studies the relationship between heat and chemical reactions.