Distinction between Work and Internal Energy

1 The work is the product of force and displacement in the direction of force. Internal energy is the energy stored in a substance in the form of molecular energy that is due to the configuration of the molecules and to the motion of the molecules and to the motion of the molecules and their parts.
2 Work is energy in transition, i.e, it exists only when a force is over coming a resistance and it is done when the force is moving through a distance. A body never contains work. The internal energy is the energy which the body contains.
3 Work flows into a system, but after it is ‘in’, it is not work. It may have been converted into any other form of energy. Internal energy may flow into or out of a system and still it may remain as internal energy or it may be converted into work or other form of energy.
4 Work is a path function. Internal energy is a point function.
5 Work has no relation to the state of a substance, which is represented by a point on a plane with properties as coordinates. Internal energy is always related to the state of the substance.
6 Work can be converted fully (100%) into heat in case of ideal heat engine. Internal energy cannot be fully converted into work even in the most perfect engine that the mind can conceive.

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