What is the standard unit for measuring the quantity of heat in a substance?

The standard unit for measuring the quantity of heat in a substance is the Joule. The Joule is a recognized unit of energy in the International System of Units (SI). It is broadly used in various scientific fields, particularly in thermodynamics, to quantify heat energy as well as work done and energy transfer.

While the British Thermal Unit (BTU) and the Calorie are also units used to measure heat energy, they are not the standard units recognized globally. The BTU is primarily used in the United States for heating and cooling systems, and the Calorie is often used in food science and nutrition. The Watt is not a unit of heat but rather a measurement of power, indicating the rate of energy transfer over time.

Understanding these distinctions clarifies why the Joule is the standard unit, as it provides a consistent and universally accepted measure across various scientific disciplines.