Enthalpy (H) is the transfer of energy in a reaction (for chemical reactions it is in the form of heat) and ΔH is the change in enthalpy. ΔH is a state function. Being a state function means that ΔH is independent of the processes between initial and final states. In other words, it does not matter what steps we take to get from initial reactants to final products—the ΔH will always be the same. ΔHrxn, or the change in enthalpy of a reaction, has the same value of ΔH as in a thermochemical equation, but is in units of kJ/mol being that it is the enthalpy change per moles of any particular substance in the equation. Values of ΔH are determined experimentally under standard conditions of 1atm and 25 °C (298.15K).