The process of is involved in the operation of all heat engines.

The process of heat exchange is involved in the operation of all heat engines.

Explanation:

A heat engine refers as the system which converts thermal or heat and chemical energy into mechanical energy. Then, these can be utilised for mechanical work. This is done by raising the active substances from higher to lower temperature state. In simple words, it produces macroscopic movement from the heat.

For example, when people rub their hands, friction converts mechanical energy (the movement of our hands) into thermal energy (hands warm up). Heat engines work exactly the opposite; they take energy to warm up (in relation to the environment) and release it for movement. This movement is often transformed into electricity by a generator.  It shows that there is exchange of heat involved in all of its processes.

this means that the temperature of both substances will be equal