Question about exergonic and endergonic reactions...?

1. Would burning gas be considered and exergonic or endergonic reaction?

When gas burns it gives off heat (excess energy). When a reaction gives off heat energy (or any other type of energy) then it is exergonic.

2. Would the production of sugars in plants by photosynthesis be exergonic or endergonic?

Plants undergo photosynthesis by allowing sunlight to add energy to the cell. When this energy is present then the production of sugars can occur from the raw materials carbon dioxide and water. Since energy must be added to the reaction then the reaction is defined as endergonic.

The definitions would apply to any chemical reaction, not just the ones mentioned. If energy is given off as a product then the reaction is exergonic. If energy is required to make a reaction proceed then the reaction is endergonic.

Hope this is helpful to you. JIL HIR I'm glad you want to learn.

Combustion is nearly the definition of energy producing reactions, so it is exergonic.

Photosynthesis is the equivalent of running the combustion reaction backwards, since O2 + H2O go to CHO and O2. So this is pretty much the definition of endergonic.