the unit in which the quantity of heat energy is usually expressed is called the ?
Joule?
After reading your next post, and answering it, you may be thinking of specific heat but I don't think that's a unit.
The unit in which the quantity of heat energy is usually expressed is called the calorie (cal).
To understand how the calorie is related to heat energy, we need to know that a calorie is defined as the amount of heat energy required to raise the temperature of 1 gram of water by 1 degree Celsius. However, the calorie is a relatively small unit, so in practical applications, a larger unit called the kilocalorie (kcal) is often used.
To find the answer to your question, you can also use various online resources or consult a physics or thermodynamics textbook that provides information on units of heat energy. Websites like Wikipedia, educational websites, or scientific journals can also give you detailed explanations about heat energy units.