For each of the following gas-phase reactions, write the rate expression in terms of the appearance of each product and disappearance of each reactant:
(a) 2 H2O(g) → 2 H2(g) + O2(g)
(b) 2 SO2(g) + O2(g) → 2 SO3(g)
(c) 2 NO(g) + 2 H2(g) → N2(g) + 2 H2O(g)
(d) N2(g) + 2 H2(g) → N2H4(g)