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4 Jan 2026
•
AQA Combined Science Chemistry Paper 2: Higher Tier
Faye Findlay
@fayefindlay_ylvf
1 / 5
Rate of Reaction & Equilibrium
Ever wondered why some reactions happen instantly whilst others take ages? The rate of reaction measures how quickly reactants transform into products, and it's all about particle collisions.
Collision theory explains that particles must crash into each other with enough energy to create a successful reaction. You can speed things up by increasing temperature (particles move faster), concentration (more particles in the same space), pressure (particles squashed together), or surface area (more exposed reaction sites).
Catalysts are like chemical matchmakers - they speed up reactions without getting used up themselves. Meanwhile, reversible reactions reach equilibrium when the forward and backward reactions happen at the same rate, shown by the ⇌ symbol.
Key Tip: Remember that Le Chatelier's Principle means equilibrium systems always fight back against changes - if you increase pressure, the system shifts to reduce it!
Hydrocarbons & Crude Oil
Hydrocarbons are simple compounds made only of carbon and hydrogen atoms, but they power our entire world! The simplest type, alkanes, follow the formula CnH2n+2 - from methane (CH4) to butane (C4H10).
Crude oil is ancient plankton that's been cooking underground for millions of years. We extract this non-renewable treasure through fractional distillation - heating it up so different compounds evaporate at different temperatures.
Longer hydrocarbon chains are thick and less flammable, whilst shorter ones are runny and highly flammable. That's why we use cracking to split long chains into more useful shorter ones and reactive alkenes.
Remember: In fractional distillation, it's hotter at the bottom (longer hydrocarbons) and cooler at the top (shorter hydrocarbons) - think of it like a chemical skyscraper!
Purity & Chemical Analysis
Pure substances are chemistry's perfectionists - they contain only one compound or element and melt or boil at exact temperatures. But most useful materials are actually formulations - carefully designed mixtures that do specific jobs perfectly.
Chromatography is your detective tool for separating mixtures. It works using a mobile phase (where molecules can move) and a stationary phase (where they can't), letting you identify mystery substances.
You can also identify gases using simple tests: chlorine turns damp litmus paper white, oxygen relights a glowing splint, and carbon dioxide makes limewater go cloudy.
Pro Tip: The further a substance travels in chromatography, the more soluble it is in the mobile phase - use this to identify unknown compounds!
Chemistry of the Atmosphere
Our atmosphere wasn't always perfect for life - it evolved through billions of years of volcanic activity and biological processes. Early volcanoes released water vapour that condensed into oceans, whilst algae and plants gradually pumped out oxygen through photosynthesis.
Greenhouse gases like carbon dioxide, methane, and water vapour act as Earth's insulating blanket. However, human activities including deforestation, burning fossil fuels, and agriculture have dramatically increased these gases.
This creates serious consequences: melting ice caps, changing rainfall patterns, and shifting storm systems. Your carbon footprint measures how much CO2 and other greenhouse gases you're responsible for throughout your lifetime.
Climate Action: Reducing our carbon footprint through renewable energy, efficient processes, and sustainable choices is crucial for our planet's future!
Using Resources Sustainably
Renewable resources can be replaced as fast as we use them, whilst non-renewable resources can't keep up with our demands. Understanding this difference is crucial for managing Earth's precious materials.
Potable water (safe drinking water) requires careful treatment: fresh water passes through filtration systems, then gets sterilised using chlorine, ozone, or UV light. It sounds simple, but clean water is a luxury many lack!
Life cycle assessment tracks a product's environmental impact from raw material extraction through manufacturing, use, and disposal. Sewage treatment involves screening, settling, aerobic treatment of liquid waste, and anaerobic digestion of solid sludge.
Sustainability Matters: Every product you use has hidden environmental costs - thinking about life cycles helps you make smarter choices for the planet!
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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
AQA Combined Science Chemistry Paper 2: Higher Tier
Faye Findlay
@fayefindlay_ylvf
Chemistry is all around you - from the air you breathe to the water you drink! This summary covers the essential reactions, compounds, and processes that shape our world, giving you the knowledge you need to ace your chemistry exams.
Rate of Reaction & Equilibrium
Ever wondered why some reactions happen instantly whilst others take ages? The rate of reaction measures how quickly reactants transform into products, and it's all about particle collisions.
Collision theory explains that particles must crash into each other with enough energy to create a successful reaction. You can speed things up by increasing temperature (particles move faster), concentration (more particles in the same space), pressure (particles squashed together), or surface area (more exposed reaction sites).
Catalysts are like chemical matchmakers - they speed up reactions without getting used up themselves. Meanwhile, reversible reactions reach equilibrium when the forward and backward reactions happen at the same rate, shown by the ⇌ symbol.
Key Tip: Remember that Le Chatelier's Principle means equilibrium systems always fight back against changes - if you increase pressure, the system shifts to reduce it!
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
Hydrocarbons & Crude Oil
Hydrocarbons are simple compounds made only of carbon and hydrogen atoms, but they power our entire world! The simplest type, alkanes, follow the formula CnH2n+2 - from methane (CH4) to butane (C4H10).
Crude oil is ancient plankton that's been cooking underground for millions of years. We extract this non-renewable treasure through fractional distillation - heating it up so different compounds evaporate at different temperatures.
Longer hydrocarbon chains are thick and less flammable, whilst shorter ones are runny and highly flammable. That's why we use cracking to split long chains into more useful shorter ones and reactive alkenes.
Remember: In fractional distillation, it's hotter at the bottom (longer hydrocarbons) and cooler at the top (shorter hydrocarbons) - think of it like a chemical skyscraper!
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
Purity & Chemical Analysis
Pure substances are chemistry's perfectionists - they contain only one compound or element and melt or boil at exact temperatures. But most useful materials are actually formulations - carefully designed mixtures that do specific jobs perfectly.
Chromatography is your detective tool for separating mixtures. It works using a mobile phase (where molecules can move) and a stationary phase (where they can't), letting you identify mystery substances.
You can also identify gases using simple tests: chlorine turns damp litmus paper white, oxygen relights a glowing splint, and carbon dioxide makes limewater go cloudy.
Pro Tip: The further a substance travels in chromatography, the more soluble it is in the mobile phase - use this to identify unknown compounds!
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
Chemistry of the Atmosphere
Our atmosphere wasn't always perfect for life - it evolved through billions of years of volcanic activity and biological processes. Early volcanoes released water vapour that condensed into oceans, whilst algae and plants gradually pumped out oxygen through photosynthesis.
Greenhouse gases like carbon dioxide, methane, and water vapour act as Earth's insulating blanket. However, human activities including deforestation, burning fossil fuels, and agriculture have dramatically increased these gases.
This creates serious consequences: melting ice caps, changing rainfall patterns, and shifting storm systems. Your carbon footprint measures how much CO2 and other greenhouse gases you're responsible for throughout your lifetime.
Climate Action: Reducing our carbon footprint through renewable energy, efficient processes, and sustainable choices is crucial for our planet's future!
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
Using Resources Sustainably
Renewable resources can be replaced as fast as we use them, whilst non-renewable resources can't keep up with our demands. Understanding this difference is crucial for managing Earth's precious materials.
Potable water (safe drinking water) requires careful treatment: fresh water passes through filtration systems, then gets sterilised using chlorine, ozone, or UV light. It sounds simple, but clean water is a luxury many lack!
Life cycle assessment tracks a product's environmental impact from raw material extraction through manufacturing, use, and disposal. Sewage treatment involves screening, settling, aerobic treatment of liquid waste, and anaerobic digestion of solid sludge.
Sustainability Matters: Every product you use has hidden environmental costs - thinking about life cycles helps you make smarter choices for the planet!
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?
You can download the app from Google Play Store and 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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Most popular content: Properties of Water
Most popular content in Chemistry
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Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.9/5
App Store
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
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