Write the basic difference between heat and internal energy.

Explanation

State of thermodynamics system is characterised by its internal energy but not by heat.
For example, a statement like .a gas in a given state has a certain amount of heat. is as meaningless as the statement that a gas in a given state has a certain amount of work.
In contrast, a gas in a given state has a certain amount of internal energy.. Similarly, the statements .a certain amount of heat is supplied to the system. or .a certain amount of work was done by the system. are perfectly meaningful.
In short, heat and work in thermodynamics are not state variables. They are modes of energy transfer to a system resulting in change in its internal energy
Heat is the mode of energy transfer.