Why is it that some reactions can occur and not others?

Answer 1

A reaction's ability to proceed depends upon reaction spontaneity, measured though Gibbs Free Energy, or ΔG (delta G). When the value for ΔG is negative, a reaction proceeds under normal conditions, and when it is positive, it will not (but can be manipulated into doing so). A most obvious example would be temperature because certain reactions need to reach the activated complex to obtain enough potential energy to occur.

Answer 2

The ability of a reaction to occur is determined by factors such as the energy required to break or form chemical bonds, the stability of the reactants and products, and the presence of a suitable pathway for the reaction to proceed. Reactions that are thermodynamically favorable and have a low activation energy are more likely to occur, while those that are energetically unfavorable or have high activation barriers may not proceed under given conditions.

Answer 3

Because some elements are inert, such as the Noble Gases in Group 8 - they have a full outer shell of electrons and therefore cannot react.

Answer 4

Some chemical reactions are non reactive because one or both of the reactants would not have valence electrons and electrons are responsible for chemical reactions.