## What is heat energy and thermal equilibrium

We know that water always flows from a higher level to a lower level, similarly heat is always transferred from a body at higher temperature to a body at lower temperature till a thermal equilibrium is attained. Hence, heat lost by a body at higher temperature is equal to heat gained by a body at lower temperature. Hence, temperature is a physical quantity which determines the direction of the flow of heat between two bodies.

the flow of heat continues till both the bodies attain the same temperature. This temperature is called equilibrium temperature. The state of two bodies at the same temperature in which there is no net flow of heat energy between them is called state of thermal equilibrium.

## Difference between heat energy and temperature

### Temperature

Temperature is the effect

A thermometer is used to measure temperature.

The S.I. unit of temperature is kelvin.

It is the average kinetic energy of the molecules.

### Heat

heat energy heat energy is the cause.

A calorimeter is used to measure heat energy.

The S.I. unit of heat is joule.

It is the sum of the potential and the kinetics energy of the molecules of the substance.