Definition of untiring for English Language Learners. : working very hard with a lot of energy for a long time : never seeming to get tired.
Enthalpy is the heat content of a chemical system. The molar enthalpy of reaction (Hrxn) is the amount of heat transferred during a reaction. It is reported in kilojoules per mole of reactant. A reaction that produces heat is exothermic and has a negative Hrxn.A reaction that absorbs heat is endothermic and has a positive Hrxn.he molar enthalpy of reaction (Hrxn) is the amount of heat transferred during a reaction. It is reported in kilojoules per mole of reactant. A reaction that produces heat is exothermic and has a negative Hrxn. A reaction that absorbs heat is endothermic and has a positive Hrxn.
The enthalpy of hydration is always exothermic, since it involves bond making. The lattice energy contribution is always endothermic, since it involves breaking the ionic bonds between the positive and negative ions in the molecule.