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12/9/2025
Chemistry
Chapter 2: Phase Changes
86
•
Dec 9, 2025
•
Understanding Phase Changes: Chemistry Notes Chapter 2
K
Karen
@karen_kysr
1 / 4
States of Matter and Properties
You encounter solids, liquids, and gases every day without realising how differently their particles behave. Solids maintain both definite volume and shape because particles are tightly packed and can't move about. Liquids keep their volume but take the shape of their container since particles can flow past each other whilst staying close together.
Gases are the rebels of the matter world - they expand to fill any container completely because their particles are spread far apart and easily compressed. Think of how air fills a balloon or how steam spreads throughout a kitchen.
Physical properties can be observed without changing what the substance actually is. These split into extensive properties (like mass and volume that depend on how much you have) and intensive properties (like melting point and density that stay the same regardless of sample size). A physical change alters appearance but keeps the same chemical composition - ice melting into water is still H₂O.
Quick Tip: Remember that physical changes are often reversible, whilst chemical changes create entirely new substances with different properties.
Chemical Changes and Pure Substances
Chemical changes are far more dramatic than physical ones - they actually create new substances with completely different compositions. Watch for telltale signs: energy transfers (heat or light), gas production, solid formation from mixing liquids, or colour changes.
The Law of Conservation of Mass is chemistry's golden rule: mass never disappears during reactions. What goes in must equal what comes out, just rearranged differently.
Elements are chemistry's building blocks - the simplest forms of matter that can't be broken down further. Compounds form when two or more elements chemically bond in fixed proportions, creating substances with entirely different properties than their original elements. Sodium (explosive metal) plus chlorine (poisonous gas) equals table salt!
Chemical symbols represent elements with one or two letters (first capitalised, second lowercase), whilst chemical formulas show compound compositions. The Law of Definite Proportions ensures compounds always contain the same element ratios regardless of sample size.
Key Point: Compounds can only be separated into elements through chemical means, not physical methods like filtering or heating.
Laws and Calculations
The percent by mass calculation helps determine how much of each element exists in a compound using the formula: (mass of element ÷ mass of compound) × 100. This becomes crucial for identifying unknown substances and checking compound purity.
The Law of Multiple Proportions explains why the same elements can form different compounds. When examining compounds like NO and NO₂, the oxygen masses that combine with the same nitrogen mass always form simple whole number ratios.
Mixtures are physical blends where substances keep their individual properties. Heterogeneous mixtures show obvious differences (like Chex mix or oil and water), whilst homogeneous mixtures appear uniform throughout (like properly mixed salt water).
Separating mixtures exploits differences in physical properties: filtration uses size differences, chromatography relies on retention factors, distillation separates by boiling points, sublimation works when only one solid can change directly to gas, and crystallisation forms pure solid particles from solutions.
Study Hack: Practice identifying mixture types around you - your lunch tray probably contains both heterogeneous and homogeneous examples!
Advanced Separation Techniques
Crystallisation represents one of the most elegant separation methods, forming pure solid particles directly from solutions. This technique proves essential in both laboratory work and industrial processes for obtaining high-purity substances.
Understanding these separation principles helps you tackle practical chemistry problems and explains how scientists isolate specific compounds from complex mixtures in real-world applications.
Real-World Connection: These separation techniques are used everywhere from water treatment plants to pharmaceutical manufacturing - mastering them opens doors to understanding countless industrial processes.
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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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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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Brad T
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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
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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
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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
Aubrey
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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
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
Understanding Phase Changes: Chemistry Notes Chapter 2
K
Karen
@karen_kysr
Matter exists in three distinct states and can undergo various changes whilst following specific laws. Understanding the differences between physical and chemical properties, elements and compounds, and how to separate mixtures forms the foundation of chemistry.
States of Matter and Properties
You encounter solids, liquids, and gases every day without realising how differently their particles behave. Solids maintain both definite volume and shape because particles are tightly packed and can't move about. Liquids keep their volume but take the shape of their container since particles can flow past each other whilst staying close together.
Gases are the rebels of the matter world - they expand to fill any container completely because their particles are spread far apart and easily compressed. Think of how air fills a balloon or how steam spreads throughout a kitchen.
Physical properties can be observed without changing what the substance actually is. These split into extensive properties (like mass and volume that depend on how much you have) and intensive properties (like melting point and density that stay the same regardless of sample size). A physical change alters appearance but keeps the same chemical composition - ice melting into water is still H₂O.
Quick Tip: Remember that physical changes are often reversible, whilst chemical changes create entirely new substances with different properties.
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Chemical Changes and Pure Substances
Chemical changes are far more dramatic than physical ones - they actually create new substances with completely different compositions. Watch for telltale signs: energy transfers (heat or light), gas production, solid formation from mixing liquids, or colour changes.
The Law of Conservation of Mass is chemistry's golden rule: mass never disappears during reactions. What goes in must equal what comes out, just rearranged differently.
Elements are chemistry's building blocks - the simplest forms of matter that can't be broken down further. Compounds form when two or more elements chemically bond in fixed proportions, creating substances with entirely different properties than their original elements. Sodium (explosive metal) plus chlorine (poisonous gas) equals table salt!
Chemical symbols represent elements with one or two letters (first capitalised, second lowercase), whilst chemical formulas show compound compositions. The Law of Definite Proportions ensures compounds always contain the same element ratios regardless of sample size.
Key Point: Compounds can only be separated into elements through chemical means, not physical methods like filtering or heating.
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Laws and Calculations
The percent by mass calculation helps determine how much of each element exists in a compound using the formula: (mass of element ÷ mass of compound) × 100. This becomes crucial for identifying unknown substances and checking compound purity.
The Law of Multiple Proportions explains why the same elements can form different compounds. When examining compounds like NO and NO₂, the oxygen masses that combine with the same nitrogen mass always form simple whole number ratios.
Mixtures are physical blends where substances keep their individual properties. Heterogeneous mixtures show obvious differences (like Chex mix or oil and water), whilst homogeneous mixtures appear uniform throughout (like properly mixed salt water).
Separating mixtures exploits differences in physical properties: filtration uses size differences, chromatography relies on retention factors, distillation separates by boiling points, sublimation works when only one solid can change directly to gas, and crystallisation forms pure solid particles from solutions.
Study Hack: Practice identifying mixture types around you - your lunch tray probably contains both heterogeneous and homogeneous examples!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Advanced Separation Techniques
Crystallisation represents one of the most elegant separation methods, forming pure solid particles directly from solutions. This technique proves essential in both laboratory work and industrial processes for obtaining high-purity substances.
Understanding these separation principles helps you tackle practical chemistry problems and explains how scientists isolate specific compounds from complex mixtures in real-world applications.
Real-World Connection: These separation techniques are used everywhere from water treatment plants to pharmaceutical manufacturing - mastering them opens doors to understanding countless industrial processes.
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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4.8/5
Google Play
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