Heat Energy and Work Energy are closely related to each other yet different. In this article let us discuss the precise difference between them from the Heat Transfer perspective of Thermodynamics.
In the previous article, we have defined Heat as the form of energy transferred between two systems by virtue of a temperature difference. Heat and Work are the interaction of energy between system and surrounding. Both Heat and Work are recognized as the boundary phenomenon.
A system may have energy but not heat or work because both heat and work are transient (in motion) phenomenon.
Both heat and work are associated with the process but not with a state. Both heat and work are path functions. They are represented by path followed during the process.
In the following figure, point 1 and 2 represents the initial state and final state of the system. The path represents process 1-2.
Heat is a low-grade energy whereas work is a high-grade energy. High-grade energy can be converted to directly converted in any form of energy such as heat energy; while low-grade energy cannot be directly converted into high-grade energy. The low-grade energies are thermal energy, heat obtained from combustion of fossil fuels, geothermal energy etc. The high-grade energies are Mechanical work, electrical energy, wind energy etc.
Heat transfer takes place due to temperature difference only. While work transfer may take place due to any potential difference in pressure, temperature, height, velocity, voltage etc.
A stationary system cannot do work while such restriction is not imposed on heat transfer.
There are some forms of work transfer such as mechanical work, electrical work, gravitational work, shaft work, flow work etc.
The Final Word about Heat Energy and Work Energy
The entire quantity of Work can be converted into Heat or any other form of energy while Heat cannot be completely converted into Work.