Since decomposition is an endergonic reaction. Does this mean it's reverse reaction synthesis is exothermic?

4 answers

The logic does not follow.The statement can be true but it may not be true, also. It depends upon the reaction. Endergonic refers to the Gibbs free energy while exothermic refers ONLY to the change in enthalpy, delta H. So you are comparing apples and oranges.
I meant endothermic not endergonic sorry.
Yes, if the reaction is endothermic in one direction, it is exothermic in the reverse direction. Thanks for clarifying the question.
I hope the question refers to a particular decomposition. Some decompositions are very exothermic and/or exergonic. The explosive decomposition of nitroglycerin and TNT are examples of that. The same applies to synthesis reactions. Not all of them are exothermic.