When gases are released from a reaction what type of change has occurred?

A chemical change has occurred.

Explanation:

A chemical change is accompanied by a change in the chemical composition of the substance.

A color change, formation of a precipitate, evolution of a gas , temperature change are the indications of a chemical change.

For example  

Here we see the formation of a precipitate or an insoluble solid

A chemical reaction is accompanied by a change in temperature.

Reaction in which heat is evolved is an exothermic reaction and reaction in which heat is absorbed is called as endothermic reaction.

Combustion reaction is an example in which heat and light is given off and it is exothermic.

Some reactions we see gas gets evolved. For example electrolysis of water produces Hydrogen and oxygen gas.

nacl is added to the aqueous of what? ? in order to get a proper answer you have to specify the exact composition of the aqueous solution.