### Theory:

In the previous chapters, we have studied:
• What is heat?
• What are all the effects of heat energy?
Heat:
Heat is one form of energy transferred between two objects, materials, and systems with different temperatures, generally from a higher to a lower temperature.
It is also known as Heat energy or Thermal energy.

When heat energy is provided to substances, physical changes take place in them.

For example, the solid form of water (ice) is turned into a liquid form, and the liquid form of water is changed to a gaseous state. These are all the physical changes due to heat energy.

Similarly, heat energy creates chemical changes also. To know more about physical and chemical changes in substances, we need to measure the amount of heat involved. The technique used to measure the amount of heat involved in a physical or chemical process is calorimetry.

Calorimetry:
Calorimetry is the science associated with determining the changes in energy of a system by measuring the heat exchanged (gained or lost) with the surroundings during a physical or chemical change.
Calorimeter:
A calorimeter is a device used to measure the quantity of heat transferred to or from an object.
Temperature:
Temperature is the physical quantity that expresses the hotness or coldness of the substance.
The temperature of the substance is the approximation of the average kinetic energy of the substance. Higher temperature means the molecules inside the substance are moving rapidly. Similarly, lower temperature means that the molecules are moving in a slow phase.

A thermometer is used to measure the temperature.

Thermometer:
It is a device used to measure the temperature or temperature gradient (the degree of hotness or coldness of the object).
Units of Temperature:
Three units are used to measure the temperature:
1. Degree Celsius (°$$C$$)
2. Fahrenheit (°$$F$$)
3. Kelvin ($$K$$)
Units of Heat:
Heat is defined as the flow of energy from hotter to cooler objects.

We know that the SI Unit of Energy is Joule. Similarly, heat can also be represented through the SI Unit "Joule". It is also measured as "Calorie".

One Calorie is the amount of heat energy necessary to increase the temperature of $$1$$ gram of water to $$1$$ °C.
We can relate, $$1$$ Calorie $$=$$ $$4.186$$ joule.