A closed system in thermodynamics refers to a system in which no mass can enter or leave, but energy can be exchanged with the surroundings. This means that the total energy of the system remains constant.
The first law of thermodynamics states that the change in internal energy of a closed system is equal to the heat added to the system minus the work done by the system. This can be expressed as ΔU = Q - W.
Heat and work are both forms of energy that can be exchanged with a closed system. Heat is the transfer of energy due to a temperature difference, while work is the transfer of energy due to a force acting through a distance.
The second law of thermodynamics states that in a closed system, the total entropy (measure of disorder) of the system and its surroundings will always increase. This means that for a closed system, processes will naturally tend towards a state of maximum entropy.
An example of a closed system in everyday life is a sealed jar of pickles. No mass can enter or leave the jar, but energy can be exchanged in the form of heat. The pickles and brine inside the jar would be considered the closed system, while the air and other surroundings outside the jar would be the surroundings.