6. Hydrogen-oxygen fuel cells are used to generate electricity. The overall reaction in a hydrogen-oxygen fuel cell is shown below.

2H_{2}(g) + O_{2}(g) -> 2H_{2}*O(l)

This reaction is exothermic.

(a) Explain the meaning of the term exothermic. [1]

(b) Explain, in terms of the energy changes associated with bond breaking and bond forming, why the reaction is exothermic. [2]

(c) A hydrogen-oxygen fuel cell uses 2000 dm³ of hydrogen measured at room temperature and pressure. Calculate the volume of oxygen, measured at room temperature and pressure, used by the fuel cell. [One mole of any gas at room temperature and pressure occupies a volume of 24 dm³.] [3]

(d) The electrode reactions in an oxygen-hydrogen fuel shell are shown below.

Equation 1 O2(g) + 2H₂O(I) + 4e → 4OH (aq) Equation 2 H2(g) + 2OH (aq) → 2e + 2H₂O(1)

Explain why the reaction in a fuel cell involves both oxidation and reduction. [2]

(e) Name one source of the hydrogen needed for a fuel-cell. [1]

(f) State one advantage and one disadvantage of using an oxygen-hydrogen fuel cell. [2]