## Chemistry: The Central Science (13th Edition)

1 mol of CO$_2$ gas has the higher enthalpy.
Enthalpy can be defined as the total amount of heat in a system. 1 mol of CO$_2$ in the gas phase will contain much more heat than 1 mol of CO$_2$ in the solid phase. This is because, the molecules in the gas phase have a higher average kinetice energy, and therefore the system with the gas must have a higher temperature.