Consider the following two processes and their enthalpy changes per mole of substance indicated.
Process X: H2O(s) → H2O(l) ΔH = +6.0kJ mol−1
Process Y: 2 H2O2(aq) → 2 H2O(l) + O2(g) ΔH = −196kJ mol−1
Which choice correctly classifies each process as physical or chemical and accounts for the sign of ΔH?
a) X is chemical and endothermic because water molecules break; Y is chemical and exothermic because O–O bonds break.
b) X is physical and endothermic because energy is needed to overcome intermolecular forces; Y is chemical and exothermic because forming stronger O–H bonds releases energy.
c) Both X and Y are physical; X is endothermic because melting requires energy, Y is exothermic because gas escapes.
d) X is physical and endothermic because energy is needed to overcome intermolecular forces; Y is chemical and endothermic because breaking the O–O bonds requires energy.