Final answer:
The standard enthalpy of formation of C3H6 gas can be determined by considering the enthalpy changes for the formation of C3H6 gas and its elements (C and H2) in their most stable forms. If the standard enthalpy of formation is negative, it is an exothermic reaction, and if it is positive, it is an endothermic reaction.
Step-by-step explanation:
The standard enthalpy of formation of a substance is the enthalpy change when one mole of the substance is formed from its elements in their standard states.
The standard enthalpy of formation of C3H6 gas is calculated by considering the enthalpy changes for the formation of C3H6 gas and its elements (C and H2) in their most stable forms.
If the standard enthalpy of formation of C3H6 gas is negative, it means the formation reaction is exothermic. If it is positive, the reaction is endothermic.