In nature, one common strategy to make thermodynamically unfavorable reactions proceed is to couple them chemically to reactions that are thermodynamically favorable. as long as the overall reaction is thermodynamically favorable, even the unfavorable reaction will proceed.
part a: consider these hypothetical chemical reactions:
a⇌b,δg= 11.9 kj/mol
b⇌c,δg= -26.7 kj/mol
c⇌d,δg= 7.30 kj/mol
what is the free energy, δg, for the overall reaction, a⇌d?