The energy of the universe is constant.

The total energy of the universe is constant; the total entropy is continually increasing.

The entropy of the universe tends to a maximum.

In all cases where work is produced by heat, a quantity of heat proportional to the work done is expended; and inversely, by the expenditure of a like quantity of work, the same amount of heat may be produced.

The energy of the universe is constant.

Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time.

The algebraic sum of all the transformations occurring in a cyclical process can only be positive, or, as an extreme case, equal to nothing. Statement of the second law of thermodynamics, 1862