Without referring to tables, predict which of the following has the higher enthalpy in each case.

(a) 1 mol CO2(s) or 1 mol CO2(g) at the same temperature.
(b) 2 mol of hydrogen atoms or 1 mol of H2.
(c) 1 mol H2(g) and 0.5 mol O2(g) at 25 °C or 1 mol H2O(g) at 25 °C.
(d) 1 mol N2(g) at 100 °C or 1 mol N2(g) at 300 °C.