4.13 understand the use of ΔH to represent molar enthalpy change for exothermic and reactions

∆H is the symbol for enthalpy change.  This means more or less the same thing as a change in heat energy, but it is usually used to represent the change for one mole of a substance (molar enthalpy change) AND it has a sign to show whether the reaction is exothermic or endothermic.  A negative sign means the reaction is exothermic, and a positive sign means the reaction is endothermic.