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.

the correct answer is:

a. formation of precipitation

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.