The enthalpy change of combustion generally increases as the mass of alcohol increases.
Enthalpy change of combustion refers to the amount of heat released or absorbed when a substance undergoes complete combustion with oxygen. It is typically measured per mole of the substance.
When the mass of alcohol increases, there are more moles of alcohol present in the system. Assuming all other conditions remain constant, the increase in the number of moles of alcohol will result in a greater quantity of heat being released or absorbed during combustion. Consequently, the enthalpy change of combustion increases.
It's worth noting that enthalpy change of combustion can also be expressed on a per-gram basis, which is referred to as specific enthalpy change of combustion. In this case, the specific enthalpy change of combustion would remain relatively constant if the alcohol being considered has a constant molar mass. However, if the molar mass of the alcohol varies with its mass, the specific enthalpy change of combustion would change accordingly.