Activation energy: The minimum amount of energy required for a chemical reaction to occur. If it's too high, even with favorable enthalpy change, the reaction may be nonspontaneous.
Equilibrium constant: A measure of how far a chemical reaction proceeds towards completion or equilibrium. If it is less than 1, it indicates that the forward reaction is nonspontaneous.
Entropy:A measure of disorder in a system. In some cases, even if there is favorable enthalpy change, if the increase in entropy isn't sufficient, the reaction may be nonspontaneous.