3. Write the equilibrium expressions for Key for the following reactions. a. 203 (8) = 3 02 (8)
b. 2 C2H4 (g) + 2 H2O(g) = 2 C2H6 (g) + O2 (g)
c. 2 H2(g) + S2(g) + 2 H2S (8)
d. 4 NH3(g) + 5 O2 (g) = 4 NO (8) + 6 H20 (8)

They can measure  the amount of energy gained or lost

Ithink it's the third answer

Remember that rust prevented by placing a sacrificial electrode in electrical contact with the iron. the sacrificial electrode must be composed of a metal that  oxidizes  more easily than iron (that is, it must be below iron in table 18.1).