Question:
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.
Author: ChemistryAnswer:
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.
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