First Law of Thermodynamics

The word "therm" means "heat" and "dynamics" means "Flow". Hence, thermodynamics means the "flow of heat". Thermodynamics is a branch of physics. It deals with the conversion of heat energy into other forms of energy. It also explains how energy affects matter. The four basic laws express all basic principles of thermodynamics. Today, I am going to elaborate on the First law of thermodynamics and I will also relate to some of its real-life applications.

First law of thermodynamics
The dynamics of heat flow - Thermodynamics

The statement of the First law of thermodynamics is as follows:

It states that the change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work W done by the system on its surroundings. 

First law of thermodynamics
First Law of Thermodynamics

This law is based on the principle of conservation of energy. The law of conservation of energy states that energy can neither be created nor be destroyed. According to thermodynamics first law, this means a closed system uses the energy supplied to it partly to do some work and partly to raise the internal energy of the system. To understand this, let us consider an example of a heat engine:

Heat engine

Heat engine

Imagine a small gas chamber whose ceiling is attached to a movable piston. If we heat the chamber, the volume of the gas changes and the gas expands. If all walls of this chamber were fixed, this would lead to a rise in the temperature of the gas. But in the present case, the top wall of the chamber is attached to a moving piston. The expanding gas applies pressure on the chamber ceiling and lifts it upwards. Hence, the heat energy is converted into mechanical energy that results in the movement of the piston. This forms a heat engine.

Here are a few important applications of the first law of thermodynamics:

Application of First law of thermodynamics

  • Refrigerators and air conditioners: Air conditioners don't actually produce cold. A mechanical pump in air conditioners compresses and transfers the heated working fluid (gas) outdoors. The heated gas exchanges heat energy with the outdoor surroundings and cools. Then, it is brought back indoors, where it is allowed to expand and cool so it can absorb heat from the indoor air. A heat exchanger helps in exchanging the heat from the gas to the surroundings and from the room to gas. Hence, the air conditioners don't just cool the room but they remove the heat from a closed room.
  • Heat pumps: A heat pump is simply an air conditioner run in reverse. A heat pump uses the heat from the compressed working fluid to warm the building. It is then transferred outside, where it expands and becomes cold. This allows it to absorb heat from the outside air, which even in winter is usually warmer than the cold working fluid. 

A steam engine is also based on thermodynamics first law. In fact, plants convert sunlight into chemical energy and humans convert the energy from food into mechanical and internal energy of our body via metabolism. All these processes follow the first law of thermodynamics. We utilize the energy gained from our food to perform some work and to increase the internal energy of our body.

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Author's message:

Nature works on some simple principles. One of these is that energy can be converted from one form to another by can neither be created nor destroyed. Another principle is that every system tries to attain a state of minimum energy and maximum stability. The simplicity and beauty of nature always fascinated me. I hope this article gives you an interesting read on the First law of thermodyamics.

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