For the more precise meaning of work and energy, we recall some relevant examples like combustion or burning of coal or natural gas produces heat. It ultimately enables the engine to work. The mechanical work spent by rubbing two crystalline solid blocks of ice generates a quantity of heat. Therefore, there has an intimate relation between heat, and work, one can yield the other quantity. It is an extensive thermodynamics property like volume or surface area because it depends on the mass of the system. On the other hand, intensive properties like temperature, pressure, density, refractive index, etc are independent of the mass of the system.
Units of heat, energy, and work
Physical quantities other than base physical quantities are called derived physical quantities. The units and dimensions of heat, energy, and work may be expressed in terms of base physical quantities by multiplication and division. From the definition of work, W = F × s, where the force (F) = maas × acceleration and acceleration = length sec-2. Hence, W = mass length2 sec-2.
|Unit of work
|Work, heat, or energy
||kg m2 sec-2 or erg
||g cm2 sec-2 or joule
The ability to doing work is called energy. Therefore, the units and dimensions of work, energy, and heat are the same. The most used unit for heat and energies are calories, kilocalories, eV, liter-atmosphere, etc.
Heat and work
Heat is another form of energy converted into all the other forms like electrical, chemical, mechanical, kinetic, or potential by producing work. The relation between heat and work is the origin of the first law of thermodynamics. It states that if or whenever heat is obtained from work, the amount of heat produced is proportional to work spent. In another word, if heat is transferred into work, there is a proportionality between the work obtained and heat disappeared.
Conversion of heat into work
Heat cannot be completely converted into work because any attempt to convert whole heat into work permanently changes the system or neighboring system. Another facts for learning chemistry or physics, when two objects with different temperatures come together, one with a higher temperature losses heat, and the other gains it.
Types of energy conversion
The production or conversation of heat into work going through a definite process, for example, when a liquid molecule freezes into solid yielding heat or water freezes into ice producing specific heat.
Electrical to mechanical
The electricity that passes through a circuit may produce the rotation of the armature of a motor used for lifting a weight or winding a spring. Conversely, the mechanical work done on the turbine blades of a hydroelectric power plant would generate electricity. These two examples suggest the conversion of electrical to mechanical energy or vice versa.
Chemical to electrical
Redox reaction between chemical elements zinc and copper sulfate produces a large amount of heat. The same chemical change is carried out in Daniell cell or battery for conversion of electrical energy.
What is internal energy?
In thermodynamics, every system has within itself a quantity of energy is called internal energy. It can be obtained by common observations,
- A liquid freezes into solid yielding heat.
- Zinc and copper sulfate in Daniell cell producing electricity.
- Steam expands from a higher to a lower pressure yielding work or mechanical work.
- Yellow phosphorus glows in oxygen producing light.
- Carbon monoxide unites with oxygen to producing carbon dioxide and heat energy.