Which of the following is the best estimate for the energy density of butter in joules per kilogram (J/kg)?

• A. 1.2 × 10^5 J/kg
• B. 8.5 × 10^8 J/kg
• C. 2.9 × 10^7 J/kg
• D. 3.0 × 10^6 J/kg

Answer: (C)

Verified step by step guidance

1. Understand that energy density is the amount of energy stored per unit mass, typically expressed in joules per kilogram (J/kg). For butter, this relates to the energy released when it is metabolized or burned.
2. Recall that fats, like butter, have a typical energy content of about 37 kJ per gram (or 37,000 J/g) when metabolized, which is a common value used in nutrition and chemistry.
3. Convert this energy content from joules per gram to joules per kilogram by multiplying by 1000, since 1 kg = 1000 g. This gives an approximate energy density in J/kg.
4. Compare the calculated value to the given options to identify which one is closest to the typical energy density of butter.
5. Choose the option that best matches the calculated energy density, understanding that butter's energy density is significantly higher than 10^5 J/kg but lower than 10^9 J/kg, typically around 10^7 J/kg.