Final answer:
The calorific value of a substance is the energy released per unit mass during complete combustion, measured in kJ/g or cal/g. To calculate it for the butter, we would need to know both the energy released and the mass of butter burned.
Step-by-step explanation:
The calorific value of a substance, often called the energy value or heat value, refers to the amount of energy produced when a certain mass of that substance is completely combusted. For butter or any food item, the calorific value is usually measured in kilojoules per gram (kJ/g) or calories per gram (cal/g).
To determine the calorific value of the butter, we should use the energy produced from the combustion and the mass of the butter that was burned. Since the student has only provided the energy produced (23.9 kJ), we're missing the mass of butter that was burned to obtain this energy. Thus, we would need the mass of butter to complete the calculation.
If we had the mass, the calculation for the calorific value would be: Calorific Value (kJ/g) = Total Energy Released (kJ) / Mass of Substance Burned (g).