Darwinism designates a distinctive form of evolutionary explanation for the history and diversity of life on earth. Its original formulation is provided in the first edition of On the Origin of Species in 1859.
The enthalpy - or internal energy - of a substance is a function of its temperature and pressure. The change in internal energy with respect to change in temperature at fixed pressure is the Specific Heat at constant pressure - cp.
In General Chemistry, the unstated premise is that you are doing reactions under constant pressure. ENTHALPY IS HEAT FLOW AT CONSTANT PRESSURE. Without going into too much derivation: #\mathbf(DeltaH = q_p)#. where #q_p# is the heat flow #q# under constant pressure conditions. Heat flow is thermal energy flow, so the units are in #J# or #kJ#. Typical enthalpy therefore has the same units. It follows from above that enthalpy of reaction, #DeltaH_rxn#, as-written, is in #kJ#. However, you would also see enthalpies of reaction tabulated for #25^@ C# and (in my book) #1 atm#.