Indicate the sign of the enthalpy change, ∆H, in the following processes carried out under atmospheric pressure and indicate whether each process is endothermic or exothermic: (a) An ice cube melts; (b) 1 g of butane 1C4H102 is combusted in sufficient oxygen to give complete combustion to CO2 and H2O.

In (a) the water that makes up the ice cube is the system. The ice cube absorbs heat from the surroundings as it melts, so ∆H is positive and the process is endothermic. In (b) the system is the 1 g of butane and the oxygen required to combust it. The combustion of butane in oxygen gives off heat, so ∆H is negative and the process is exothermic.