Which of the following correctly describes the standard enthalpy change of combustion?

The standard enthalpy change of combustion refers specifically to the amount of heat energy released when a substance, typically a hydrocarbon or other fuel, undergoes complete combustion in the presence of excess oxygen. This reaction converts the reactants into products, primarily carbon dioxide and water, and is measured under standard conditions (usually at 1 atmosphere of pressure and a specified temperature, often 25 °C).

The significance of this term lies in its application in various fields, such as energy production, thermodynamics, and environmental science. Knowing the enthalpy change of combustion allows for calculations related to energy yields from fuels, which is vital for understanding energy resources and their environmental impacts.

The other options describe different thermal processes that do not pertain to combustion. For instance, the enthalpy change for melting relates to phase transitions from solid to liquid, while changes involving a solid becoming a gas or a gas condensing focus on different aspects of matter change and heat transfer that are unrelated to the combustion process. Hence, the definition provided in the correct choice accurately encapsulates the essence of the standard enthalpy change of combustion.