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Laws of Thermodynamics

4 min readโ€ขdecember 10, 2021

Sitara H

Sitara H

Sitara H

Sitara H

Simple Ways to Understand the First 2 Laws of Thermodynamics

Open & Closed Systems

When discussing thermodynamics and energy transfer between two states, it's important to remember the two types of systems present: open and closed. ๐Ÿšช

Open Systems

An open system CAN exchange both matter and energy with its surroundings. An excellent example of this is liquid heating on the stovetop, as both energy (the heat) and matter (the water vapor caused by the liquid evaporating) are lost to the air. ๐Ÿ›ซ

If you're reading a problem and it doesnโ€™t ask you to not take things like air pressure or friction into account, then always assume that you are dealing with an open system. ๐Ÿ’ฏ

Closed Systems

In contrast, a closed system CANNOT exchange matter or energy with its surroundings. An example of a closed system is a liquid enclosed in a pot with a lid on top. ๐Ÿ”’

When tackling problems that say there is โ€œno need to account for air pressure in your calculations,โ€ for example, you know that you are dealing with a closed system.

๐Ÿ’ก Note: No transfer of energy that naturally takes place in nature can be completely energy-efficient. Often, at least a little energy is released as heat (๐Ÿ”ฅ) or sound (๐Ÿ”Š) when any chemical reactions occur. Therefore, almost any naturally occurring system can be classified as an open system. However, closed systems are often utilized in problems as theoretical situations to simplify them for student understanding.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-kjil3rsziqZm.png?alt=media&token=84474f1f-f577-4a06-9244-a8be058502d8

Image Courtesy of Wikipedia

The 1st Law of Thermodynamics 1

The first law refers to the universe as a whole. Still, its basic principles can be applied when considering any system or any problem related to the amount of energy present in a system! ๐Ÿ˜ฑ

The law states that the total amount of energy in the universe doesnโ€™t change, but that it can only change form or be transferred from one object to another! โšก

Applying the Law

This law seems abstract in theory and difficult to comprehend, but its applications start to make a lot more sense once you look at a few examples. ๐Ÿ˜‰

In fact, the essential idea to remember here is that the total amount of energy doesnโ€™t change when dealing with any closed system, regardless of how big the system is.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-2AGML85CcnuL.png?alt=media&token=8df95365-8894-43de-8959-89bb79f784ef

Image Courtesy of ย Wikimedia

Examples

  • Light bulbs transform electrical energy into light energy ๐ŸŒž

  • The process of photosynthesis: Plants convert light energy present in sunlight into chemical energy stored in organic molecules for their usage as a food source. ๐ŸŒฑ

๐Ÿ’ก Note: As mentioned earlier, none of these naturally occurring processes are entirely efficient, with some energy almost always being lost as heat. However, the total amount of energy present both before and after the process remains the same.

The 2nd Law of Thermodynamics 2

Weโ€™ve already established that energy cannot be created or destroyed, but it can change from more valuable forms to less useful ones. In every real-world transfer from one energy type to another, some amount of energy is converted to a form that is unavailable to do work (therefore โ€œuseless.โ€) As weโ€™ve mentioned before, in most cases, this unusable form is what we know as heat. ๐Ÿ”ง

๐Ÿ’ก Note: Heat can do work in some circumstances, but it can ALMOST NEVER be converted to another energy form with 100% efficiency. As a result, some energy will almost always be lost to a โ€œuselessโ€ category, heat or not.

Entropy

So, what happens to all this excess heat? If itโ€™s not doing work of some sort, then it is said by scientists to be increasing the levels of โ€œdisorderโ€ in the universe. ๐Ÿ’ฉ

While this might not make so much sense at first thought, think about it this way: When a hot and cool liquid are both emptied into one container, they donโ€™t stay as separate fluids on each side of the container. Instead, they both gradually mix, until all of the liquid in the container is set at an average temperature, with hot and cold particles spread evenly throughout. ๐Ÿฅค

Even though this mixture of hot and cold particles is technically in a more disordered state than when we started, it's the natural state that the mixture shifts toward, with or without our interference. ๐Ÿฅ„

In the same way, the excess heat from any reaction tends to dissipate throughout the universe evenly, increasing the degree of its disorderliness naturally. This is said to increase the universeโ€™s entropy, which is its degree of randomness or disorderliness. ๐Ÿ˜ต

The 2nd law of thermodynamics states that every energy transfer that takes place will increase the universeโ€™s entropy, reducing the amount of usable energy available to do work.

Key Takeaways

To sum up what you've read in a couple of sentences:

  • The 1st Law of Thermodynamics tells us about the conservation of energy: no energy can be created or destroyed, only transformed between different types. ๐Ÿฅฑ

  • The 2nd Law of Thermodynamics states how each process takes the universe, overall, from a state of lower to higher entropy. ๐Ÿ“ˆ

And that's a wrap! Now, I dare you to think of both thermodynamics laws as you observe events in your everyday life like a ball bouncing and your room getting messier and messier each day. ๐Ÿ›Œ

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-O3GUL1pzAxjZ.png?alt=media&token=c26d836c-4ccc-41a9-b9e9-50429ad0e566

Image Courtesy of ScienceABC

Laws of Thermodynamics

4 min readโ€ขdecember 10, 2021

Sitara H

Sitara H

Sitara H

Sitara H

Simple Ways to Understand the First 2 Laws of Thermodynamics

Open & Closed Systems

When discussing thermodynamics and energy transfer between two states, it's important to remember the two types of systems present: open and closed. ๐Ÿšช

Open Systems

An open system CAN exchange both matter and energy with its surroundings. An excellent example of this is liquid heating on the stovetop, as both energy (the heat) and matter (the water vapor caused by the liquid evaporating) are lost to the air. ๐Ÿ›ซ

If you're reading a problem and it doesnโ€™t ask you to not take things like air pressure or friction into account, then always assume that you are dealing with an open system. ๐Ÿ’ฏ

Closed Systems

In contrast, a closed system CANNOT exchange matter or energy with its surroundings. An example of a closed system is a liquid enclosed in a pot with a lid on top. ๐Ÿ”’

When tackling problems that say there is โ€œno need to account for air pressure in your calculations,โ€ for example, you know that you are dealing with a closed system.

๐Ÿ’ก Note: No transfer of energy that naturally takes place in nature can be completely energy-efficient. Often, at least a little energy is released as heat (๐Ÿ”ฅ) or sound (๐Ÿ”Š) when any chemical reactions occur. Therefore, almost any naturally occurring system can be classified as an open system. However, closed systems are often utilized in problems as theoretical situations to simplify them for student understanding.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-kjil3rsziqZm.png?alt=media&token=84474f1f-f577-4a06-9244-a8be058502d8

Image Courtesy of Wikipedia

The 1st Law of Thermodynamics 1

The first law refers to the universe as a whole. Still, its basic principles can be applied when considering any system or any problem related to the amount of energy present in a system! ๐Ÿ˜ฑ

The law states that the total amount of energy in the universe doesnโ€™t change, but that it can only change form or be transferred from one object to another! โšก

Applying the Law

This law seems abstract in theory and difficult to comprehend, but its applications start to make a lot more sense once you look at a few examples. ๐Ÿ˜‰

In fact, the essential idea to remember here is that the total amount of energy doesnโ€™t change when dealing with any closed system, regardless of how big the system is.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-2AGML85CcnuL.png?alt=media&token=8df95365-8894-43de-8959-89bb79f784ef

Image Courtesy of ย Wikimedia

Examples

  • Light bulbs transform electrical energy into light energy ๐ŸŒž

  • The process of photosynthesis: Plants convert light energy present in sunlight into chemical energy stored in organic molecules for their usage as a food source. ๐ŸŒฑ

๐Ÿ’ก Note: As mentioned earlier, none of these naturally occurring processes are entirely efficient, with some energy almost always being lost as heat. However, the total amount of energy present both before and after the process remains the same.

The 2nd Law of Thermodynamics 2

Weโ€™ve already established that energy cannot be created or destroyed, but it can change from more valuable forms to less useful ones. In every real-world transfer from one energy type to another, some amount of energy is converted to a form that is unavailable to do work (therefore โ€œuseless.โ€) As weโ€™ve mentioned before, in most cases, this unusable form is what we know as heat. ๐Ÿ”ง

๐Ÿ’ก Note: Heat can do work in some circumstances, but it can ALMOST NEVER be converted to another energy form with 100% efficiency. As a result, some energy will almost always be lost to a โ€œuselessโ€ category, heat or not.

Entropy

So, what happens to all this excess heat? If itโ€™s not doing work of some sort, then it is said by scientists to be increasing the levels of โ€œdisorderโ€ in the universe. ๐Ÿ’ฉ

While this might not make so much sense at first thought, think about it this way: When a hot and cool liquid are both emptied into one container, they donโ€™t stay as separate fluids on each side of the container. Instead, they both gradually mix, until all of the liquid in the container is set at an average temperature, with hot and cold particles spread evenly throughout. ๐Ÿฅค

Even though this mixture of hot and cold particles is technically in a more disordered state than when we started, it's the natural state that the mixture shifts toward, with or without our interference. ๐Ÿฅ„

In the same way, the excess heat from any reaction tends to dissipate throughout the universe evenly, increasing the degree of its disorderliness naturally. This is said to increase the universeโ€™s entropy, which is its degree of randomness or disorderliness. ๐Ÿ˜ต

The 2nd law of thermodynamics states that every energy transfer that takes place will increase the universeโ€™s entropy, reducing the amount of usable energy available to do work.

Key Takeaways

To sum up what you've read in a couple of sentences:

  • The 1st Law of Thermodynamics tells us about the conservation of energy: no energy can be created or destroyed, only transformed between different types. ๐Ÿฅฑ

  • The 2nd Law of Thermodynamics states how each process takes the universe, overall, from a state of lower to higher entropy. ๐Ÿ“ˆ

And that's a wrap! Now, I dare you to think of both thermodynamics laws as you observe events in your everyday life like a ball bouncing and your room getting messier and messier each day. ๐Ÿ›Œ

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-O3GUL1pzAxjZ.png?alt=media&token=c26d836c-4ccc-41a9-b9e9-50429ad0e566

Image Courtesy of ScienceABC



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APยฎ and SATยฎ are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.


ยฉ 2024 Fiveable Inc. All rights reserved.

APยฎ and SATยฎ are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.