A chemical reaction that proceeds spontaneously _____.
must run in the direction that lowers the free energy
must produce products that are more ordered than the reactant molecules
must proceed without an input of external energy
must take place in a very short amount of time
To answer the question above, remember that the chemical reactions that proceed spontaneously need not have an external energy to drive the reaction. Therefore the answer to this item is the third choice, "must proceed without an input of external energy".