Closed System:

The system that can exchange energy with the surrounding but not the mass. The quantity of matter hence remains fixed. And the system can be described as control mass system.
The physical nature and chemical composition of mass of system can change.
Water can evaporate into steam or steam can condense into water. A chemical reaction can occur between two or more components of closed system.

For instance

1. Car battery, Electric supply takes place from and to the battery but there is no transfer of material.

2. Tea kettle, Heat is supplied to kettle but mass of water is constant.

3. Water in a tank

4. Piston – cylinder assembly.