When water is produced in a combustion process, the enthalpy of combustion depends on whether water ends up as a liquid or vapor. The difference may be significant, because the latent heat of condensation is large. Fuels are often defined by a higher heating value (HHV) and a lower heating value (LHV). The HHV is defined as the "amount of heat released by a specified quantity (initially at 25C) once it is combusted and the products have returned to a temperature of 25C Which heating value considers water as a vapor and which as a liquid? Compute the HHV and LHV for combustion of methane (the dominant component of natural gas) and show how the two values are related.