What unit of energy is defined as the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius?

The correct unit of energy defined as the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius is the calorie. This definition underscores the calorie's significance in nutrition and thermodynamics, as it provides a practical means of measuring energy changes in biological systems and food energy content.

In nutritional contexts, when discussing how much energy foods provide, calories are used to quantify that energy. The concept is fundamental in both dietary planning and scientific research involving metabolic processes. The calorie's connection to water also makes it crucial for understanding how heat transfer works in physical and chemical changes—water's high specific heat capacity means it can absorb a lot of heat without a significant change in temperature, making it a useful reference point for energy measurements.

Other units like the joule and kilojoule measure energy but are not specifically defined in relation to water, while the British Thermal Unit (BTU) is related to heating but is defined as the amount of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit, which differs from the definition of a calorie.