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Properties of Gases
Gases have special properties that make them behave differently from solids and liquids. Unlike other states of matter, gases expand to fill their containers completely and can be compressed or expanded easily.
The behavior of gases can be explained by the Kinetic Molecular Theory, which tells us that gas particles are constantly moving in random directions, colliding with each other and with container walls.
Fun Fact: Gas molecules move extremely fast—up to 1,000 mph at room temperature—which is why smells spread so quickly through a room!
Low Density
Gases have low density because their molecules are spread far apart from each other. This scattered arrangement means that the same amount of substance takes up much more space as a gas than it does as a solid or liquid.
This property explains why gases are lightweight and why they rise in liquids—there's simply less mass per unit of volume in a gas.
Indefinite Shape and Volume
Unlike solids and liquids, gases have neither a definite shape nor a definite volume. They expand to take the shape and fill the volume of whatever container holds them.
This happens because gas molecules move randomly and freely, with lots of empty space between them. When you transfer a gas to a larger container, the molecules spread out to fill the available space.
When you move gas to a smaller container, the molecules get pushed closer together but still fill the entire container.
Remember: The volume of a gas is simply the volume of its container—gases always expand to fill their available space!
Compressibility and Expandability
Gases are highly compressible because of the large empty spaces between their molecules. When pressure is applied, these molecules can be forced closer together, decreasing the volume significantly.
Similarly, gases can expand dramatically when pressure decreases or temperature increases. This explains why a sealed bag of chips might puff up at high altitudes where air pressure is lower.
This property is what makes gases useful in many applications, from air bags in cars to pneumatic tools and systems.
Diffusivity
Diffusion is the process where gas molecules spread out and mix completely with other gases. Because gas molecules move quickly and have lots of space between them, diffusion happens rapidly.
When you spray perfume in one corner of a room, the scent molecules quickly spread throughout the entire space. This happens because the gas molecules are constantly moving and colliding with each other.
Different gases will always mix thoroughly to create a homogeneous mixture, meaning the composition is the same throughout. This is why our atmosphere has a consistent composition even though it contains multiple gases.
Kinetic Molecular Theory
The Kinetic Molecular Theory explains gas behavior by describing how gas particles move. According to this theory, gas particles:
- Are in constant, random motion
- Have negligible volume compared to the space between them
- Experience perfectly elastic collisions (no energy is lost)
- Have no attractive or repulsive forces between them
The theory states that the average kinetic energy of gas particles is directly proportional to absolute temperature. This means that as temperature increases, gas particles move faster on average.
Think about it: When you heat a gas, you're giving its molecules more energy to move faster, which causes them to spread out more and increase the pressure if in a closed container.
Pressure
Pressure is the force per unit area exerted by gas particles hitting the walls of a container. Each time a gas molecule bounces off a wall, it exerts a tiny force—billions of these collisions create measurable pressure.
Pressure can be measured in several units:
- Atmosphere (atm): Based on average sea-level air pressure
- Millimeters of mercury (mm Hg): Height of a mercury column
- Torr: Nearly identical to mm Hg
- Pascal (Pa): The SI unit of pressure
When you pump air into a bike tire, you're increasing the number of molecules in the same volume, causing more collisions with the walls and increasing pressure.
Volume
The volume of a gas equals the volume of its container because gases expand to fill whatever space is available to them. This is different from solids and liquids, which maintain their own volumes.
Gas volume is typically measured in:
- Milliliters (mL)
- Liters (L)
- Cubic centimeters (cm³)
When performing gas law calculations, it's important to use consistent units for volume. If you're given a volume in cubic feet but need liters, you'll need to convert before solving your problem.
Visualization tip: A standard 2-liter soda bottle contains about 2 liters of gas when empty—gases always fill their container completely!
Temperature
When working with gas laws, temperature must always be expressed in Kelvin (K), not in Celsius or Fahrenheit. This is because the Kelvin scale starts at absolute zero—the theoretical temperature at which gas molecules would have no kinetic energy.
To convert from Celsius to Kelvin, use the simple formula: K = C + 273
For example, room temperature (25°C) is 298 K on the Kelvin scale. Using the proper temperature scale is crucial because gas behavior is directly related to the absolute temperature.
Amount of Gas (Moles)
The amount of gas in a container is typically expressed in moles (n). A mole represents 6.022 × 10²³ particles (Avogadro's number), whether they're atoms or molecules.
Using moles allows us to work with manageable numbers instead of the astronomical number of actual particles. This is especially useful when working with the Ideal Gas Law and other gas equations.
The number of moles of a gas directly affects its pressure and volume. More moles mean more particles, which create more collisions and higher pressure in a fixed volume.
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This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
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Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
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I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
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Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
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I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
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Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
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This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
Understanding Gas Properties
Gases are all around us, making up our atmosphere and playing a crucial role in everyday life. They have unique properties that make them different from solids and liquids, and understanding these properties helps us explain everything from how we... Show more
Properties of Gases
Gases have special properties that make them behave differently from solids and liquids. Unlike other states of matter, gases expand to fill their containers completely and can be compressed or expanded easily.
The behavior of gases can be explained by the Kinetic Molecular Theory, which tells us that gas particles are constantly moving in random directions, colliding with each other and with container walls.
Fun Fact: Gas molecules move extremely fast—up to 1,000 mph at room temperature—which is why smells spread so quickly through a room!
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Low Density
Gases have low density because their molecules are spread far apart from each other. This scattered arrangement means that the same amount of substance takes up much more space as a gas than it does as a solid or liquid.
This property explains why gases are lightweight and why they rise in liquids—there's simply less mass per unit of volume in a gas.
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Indefinite Shape and Volume
Unlike solids and liquids, gases have neither a definite shape nor a definite volume. They expand to take the shape and fill the volume of whatever container holds them.
This happens because gas molecules move randomly and freely, with lots of empty space between them. When you transfer a gas to a larger container, the molecules spread out to fill the available space.
When you move gas to a smaller container, the molecules get pushed closer together but still fill the entire container.
Remember: The volume of a gas is simply the volume of its container—gases always expand to fill their available space!
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Compressibility and Expandability
Gases are highly compressible because of the large empty spaces between their molecules. When pressure is applied, these molecules can be forced closer together, decreasing the volume significantly.
Similarly, gases can expand dramatically when pressure decreases or temperature increases. This explains why a sealed bag of chips might puff up at high altitudes where air pressure is lower.
This property is what makes gases useful in many applications, from air bags in cars to pneumatic tools and systems.
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Diffusivity
Diffusion is the process where gas molecules spread out and mix completely with other gases. Because gas molecules move quickly and have lots of space between them, diffusion happens rapidly.
When you spray perfume in one corner of a room, the scent molecules quickly spread throughout the entire space. This happens because the gas molecules are constantly moving and colliding with each other.
Different gases will always mix thoroughly to create a homogeneous mixture, meaning the composition is the same throughout. This is why our atmosphere has a consistent composition even though it contains multiple gases.
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Kinetic Molecular Theory
The Kinetic Molecular Theory explains gas behavior by describing how gas particles move. According to this theory, gas particles:
- Are in constant, random motion
- Have negligible volume compared to the space between them
- Experience perfectly elastic collisions (no energy is lost)
- Have no attractive or repulsive forces between them
The theory states that the average kinetic energy of gas particles is directly proportional to absolute temperature. This means that as temperature increases, gas particles move faster on average.
Think about it: When you heat a gas, you're giving its molecules more energy to move faster, which causes them to spread out more and increase the pressure if in a closed container.
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Pressure
Pressure is the force per unit area exerted by gas particles hitting the walls of a container. Each time a gas molecule bounces off a wall, it exerts a tiny force—billions of these collisions create measurable pressure.
Pressure can be measured in several units:
- Atmosphere (atm): Based on average sea-level air pressure
- Millimeters of mercury (mm Hg): Height of a mercury column
- Torr: Nearly identical to mm Hg
- Pascal (Pa): The SI unit of pressure
When you pump air into a bike tire, you're increasing the number of molecules in the same volume, causing more collisions with the walls and increasing pressure.
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By signing up you accept Terms of Service and Privacy Policy
Volume
The volume of a gas equals the volume of its container because gases expand to fill whatever space is available to them. This is different from solids and liquids, which maintain their own volumes.
Gas volume is typically measured in:
- Milliliters (mL)
- Liters (L)
- Cubic centimeters (cm³)
When performing gas law calculations, it's important to use consistent units for volume. If you're given a volume in cubic feet but need liters, you'll need to convert before solving your problem.
Visualization tip: A standard 2-liter soda bottle contains about 2 liters of gas when empty—gases always fill their container completely!
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Temperature
When working with gas laws, temperature must always be expressed in Kelvin (K), not in Celsius or Fahrenheit. This is because the Kelvin scale starts at absolute zero—the theoretical temperature at which gas molecules would have no kinetic energy.
To convert from Celsius to Kelvin, use the simple formula: K = C + 273
For example, room temperature (25°C) is 298 K on the Kelvin scale. Using the proper temperature scale is crucial because gas behavior is directly related to the absolute temperature.
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Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Amount of Gas (Moles)
The amount of gas in a container is typically expressed in moles (n). A mole represents 6.022 × 10²³ particles (Avogadro's number), whether they're atoms or molecules.
Using moles allows us to work with manageable numbers instead of the astronomical number of actual particles. This is especially useful when working with the Ideal Gas Law and other gas equations.
The number of moles of a gas directly affects its pressure and volume. More moles mean more particles, which create more collisions and higher pressure in a fixed volume.
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user