Heat

1. Heat

Heat is a form of energy that transfers from a hotter object to a cooler object until they reach thermal equilibrium (the same temperature). It occurs only when there is a temperature difference between two objects. All objects store some amount of internal heat energy within them.

2. Temperature

Temperature measures the kinetic energy (motion) of molecules in an object. Higher molecular movement → Higher temperature.

3. Internal Energy

This is the total energy of all molecules within a substance. Includes kinetic energy (due to motion) and potential energy (due to intermolecular forces).

4. Specific Heat

Specific heat (also called heat capacity) is the amount of energy  required to raise the temperature of a unit mass of a substance by one degree Celsius. Different substances have different specific heat values, which determine how quickly they heat up or cool down.

5. Units of Heat

• SI Unit: Joule (J): The amount of energy required to raise the temperature of a given mass by 1°C.
• CGS Unit: Calorie (cal): The amount of heat required to increase the temperature of 1 gram of water by 1°C (from 14.5°C to 15.5°C).
• Kilocalorie (kcal): The heat required to increase the temperature of 1 kg of water by 1°C. 1 kcal = 1000 cal.

Conversions:

• 1 calorie (cal) = 4.18 Joules (J).
• 1 kilocalorie (kcal) = 1000 calories = 4180 Joules (J)

The sum of the potential energy and kinetic energy of a molecule is called its internal energy.

The total internal energy of all the molecules of a substance is called its thermal energy.

Heat is that form of energy which flows from a hot body to a cold body when they are kept in contact.

The measurement of the quantity of heat is called calorimetry.

• Heat is the energy that flows from a hot body to a cold body when they are kept in contact.
• The S.I. unit of heat is joule (J), while calorie and kilocalorie are commonly used units.
• One calorie is approximately equal to 4.2 joule, and kilocalorie is used to measure the energy value of foods.