Question

Burning H2 (g) in the presence of O2 (g) proceeds by the following reaction:

                       

H2 (g) + ½ O2 (g) --> H2O (g)                       eq. 1

In a fuel cell, the oxidation half-reaction occurring at the anode (a solid conductor) is:

H2 (g) --> 2H+ (aq) + 2e- eq. 2

At the cathode (solid conductor), O2 is reduced:

O2 (g) + 4H+ (aq) + 4e- --> 2H2O (l) eq. 3

Using Hess’s Law, estimate the heat released by oxidizing 1.0 kg (495 mol) of H2 in a fuel cell. Note that the physical state of water is different in equations 1 and 3. The heat of vaporization () of water is 40.7 kJ/mol. Hint: Start by combining the half reactions and canceling species that appear on both sides.

A. 121.4 MJ

B. 660.0 J

C. 141.6 MJ

D. 161.7 MJ

Answer 1