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K
Karen
12/12/2025
Chemistry
Chapter 2: Phase Changes
86
•
12 Dec 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 has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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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.
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very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
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I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
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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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
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
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
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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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
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!
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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 a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
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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
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
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
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
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
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
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 apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user