When ice melts, its temperature does not rise and hence its kinetic energy remains constant. The amount of energy taken by the ice is used in deriving the molecules of ice apart and it is stored in the form of potential energy. Thus, heat can be said as a form of potential energy.
The ordinary steam engines do nit satisfy the ideal conditions stated in carnot engine namely
1) Water does not absorb heat at constant temperature.
2) Condensation of steam takes place before adiabatic expansion is completed.
3) The valves of cylinder are not opened at right time.
4) Some heat escapes through conduction.
Thus efficiency of steam engines is low.
Engineering