Difference Between First Law of Thermodynamics and Second Law of Thermodynamics

Main Difference

The main difference between first law of thermodynamics and second law of thermodynamics is that the first law of thermodynamics discussed that energy could neither be created nor be destroyed, but it can change its form whereas according to the second law of thermodynamics entropy of a system always increases.

First Law of Thermodynamics vs. Second Law of Thermodynamics

The word ‘thermodynamics‘ is the derivative of a Greek word, where “Thermo” stands for heat and “dynamics” means power. So, it is the study of energy that exists in different forms like heat, light, electrical and chemical energy. There are four different laws of thermodynamics, i.e., zeroth law, first law, second law, and the third law. But the most important is the first and second laws of thermodynamics. The first law of thermodynamics discussed that energy could neither be generated nor be destroyed, but it can only change its form whereas the second law of thermodynamics states that entropy of a system never decreases but always increases. While discussing these laws, two terms are very important, i.e., system and surroundings. Any item or group of item in which we are dealing with that may be small like a cell or large like an ecosystem is known as a system. Everything present around the system is known as its surroundings.

Comparison Chart

First Law of ThermodynamicsSecond Law of Thermodynamics
The first law of thermodynamics discussed that energy could not be created or destroyed, but it can change its form.The second law of thermodynamics is the law that states that the entropy of a system never decreases but always increases.
Also Known As
It is also called the “law of conservation of energy.”The second law of thermodynamics is also called the “law of increased entropy.”
Equation
ΔE=q + w is the equation of first law of thermodynamics which is used to calculate a value if the other two quantities are known.ΔS = ΔS system + ΔS surroundings is the equation of the second law of thermodynamics to measure the overall entropy change of the system.
Expression
It’s equation express that the change in the internal energy of a system is equal to the total heat that flows into the system and work are done on the system by the surrounding.The Second law of thermodynamics expresses that The total change in the entropy is equal to the sum of the change in the entropy of the system and its surroundings.
Examples
During photosynthesis, plants use the sunlight, i.e., solar energy and convert it into chemical energy, i.e., glucose.

· We are transforming chemical energy from our meal into kinetic energy as we walk, breathe, and run, etc.

A heater in the room uses the electric energy and provides heat to the room, while in return the room can’t provide the same energy to the heater.

What is the First Law of Thermodynamics?

The first law of thermodynamics that is also called the law of conservation of energy discussed the total energy in the universe. It states that this total amount of energy remains the same. According to this law, energy can change its form, but it cannot be created or destroyed.

Examples

  1. During photosynthesis, plants use the sunlight, i.e., solar energy and convert it into chemical energy, i.e., glucose.
  2. When we walk, breathe or run, etc. after a meal, we are converting chemical energy from our meal into kinetic energy.
  3. A lighten electric bulb is converting electrical energy into light energy.

Equation

ΔE=q+w It’s equation express that the change in the internal energy of a system is equal to the total heat that flows into the system and work are done on the system by the surrounding. It can be used to calculate a value if the other two quantities are known.

What is the Second Law of Thermodynamics?

According to this law of thermodynamics, the entropy of a system never decreases but always increases. The entropy is the disorder or degree of randomness in a system. The first law states that energy can never be generated or destroyed which means energy can be recycled again and again. But, According to the Kelvin-Plancks statement, there is no system that can convert energy in different forms with 100% efficiency. It’s mean that some amount of energy is always lost into useless form in a process. So, the entropy of a system always increases. The Second Law of thermodynamics also explains that the energy transformation takes place in a particular direction only, which was not cleared in the first law of thermodynamics.

Examples

  1. An electric bulb can convert electric energy into light energy, but the reverse process is not possible, that if we provide the same amount of heat and light to the bulb, it changes it into electric energy.
  2. A heater in the room uses the electric energy and provides heat to the room, while in return the room can’t provide the same energy to the heater.

Equation

ΔS = ΔSsystem + ΔSsurroundings It is the equation that is used to measure the overall entropy change of the system.

Key Differences

  1. The first law of thermodynamics is about the energy that states that energy can never be generated or destroyed but can only change into different forms while second law of thermodynamics is the law that states that entropy of a system never decreases but always increases.
  2. The first law of thermodynamics is also called as the “law of conservation of energy,” on the other hand, the second law of thermodynamics is also called as “Law of Increased Entropy.”
  3. ΔE=q + w is the equation of first law of thermodynamics which is used to calculate a value if other two quantities are known conversely the Second law of thermodynamics express that The total change in the entropy is equal to the sum of the change in the entropy of the system and its surrounding
  4. The equation of first law of thermodynamics express that, the change in the internal energy of a system is equal to the total heat that flows into the system and work are done on the system by the surrounding. On the flip side, the Second law of thermodynamics expresses that the total change in the system can be obtained by the sum of the change in the entropy of the system and the surroundings.
  5. The example of first law of thermodynamics is photosynthesis in which plants convert solar energy into chemical energy, i.e., glucose whereas A heater in the room is an example of second law of thermodynamics that uses the electric energy and provides heat to the room, while in return the room can’t provide the same energy to the heater.

Comparison Video

YouTube video

Conclusion

According to the above discussion, it is summarized that according to the first law of thermodynamics energy can never be generated or destroyed but can only be converted into different forms, but it cannot explain the direction of energy transformation which was cleared by the second law of thermodynamics which states that entropy of a system always increases.

Author:

Harlon Moss

Harlon currently works as a quality moderator and content writer for Turpy Media. He graduated from the University of California in 2010 with a degree in Computer Science. Follow him on Twitter @HarlonMoss or on Pinterest @HarlonMoss

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