Question

An aqueous solution of NaOH can dissolve an aluminum sheet in the reaction: 2 Al+ 2 NaOH+ 2 H2O > 2 NaAlO2 + 3 H2

Answer 1

You cannot balance Al + NaOH = NaAlO2 + H2 because that reaction will not run. You can never get 2 oxygen atoms on the right hand side of the equation without also getting 2 Na atoms there. This equation will never balance.

What you need is to assume that the NaOH is aqueous, so there is water present. Then:

Al + NaOH + H2O = NaAlO2 + 1.5H2(g)

ΔG(20C) = -455.5kJ (negative, so the reaction runs)

ΔH(20C) = -474.9kJ (negative, so the reaction is exothermic)