One kilocalorie is the amount of heat needed to raise the temperature of how many kilograms of water by how many degrees Celsius?

• A. 1 kilogram by 2 degrees Celsius
• B. 1 kilogram by 1 degree Celsius
• C. 2 kilograms by 1 degree Celsius
• D. 2 kilograms by 2 degrees Celsius

Answer: (B)

The key idea is how a kilocalorie is defined for water. For water, the amount of heat needed to raise its temperature by 1 degree Celsius is defined per kilogram: 1 kilocalorie per kilogram per degree Celsius. That means one kilocalorie equals the energy required to raise 1 kilogram of water by 1°C. On nutrition labels, the term “calorie” actually refers to a kilocalorie. So the correct statement is that one kilocalorie is the heat needed to raise 1 kilogram of water by 1°C. If you used more mass or a larger temperature rise, you'd need more kilocalories (e.g., 1 kg by 2°C would require 2 kcal; 2 kg by 1°C would require 2 kcal; 2 kg by 2°C would require 4 kcal).