Final answer:
In an engine, the difference between the heat input and the heat released constitutes the work done by the system. This is a key principle of heat engines, which convert thermal energy into mechanical work, though not all heat can be converted due to system inefficiencies.
Step-by-step explanation:
In an engine, the difference between the heat put in (Qh) and the heat discharged (Qc) will appear as the work done by the system. This is a fundamental concept in thermodynamics where heat engines convert thermal energy into mechanical work. The work done can then be used to power various mechanical devices, such as a car's engine.
Heat engines operate by transferring energy from a hot reservoir (high temperature source) to a cold reservoir (low temperature sink), and in the process, they perform work (W). This is exemplified in the internal combustion engine, where a mixture of air and fuel is ignited, creating high-temperature gas that expands and pushes a piston, doing work in the process. However, not all the heat can be converted to work due to inefficiencies and the second law of thermodynamics, which means some heat is always released into the environment, commonly known as exhaust.