Chemistry can seem overwhelming at first, but these fundamental concepts... Show more
Chemistry
English Literature
Sociology
BiologySign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
437
•
Updated Mar 12, 2026
•
GCSE Chemistry Paper 1 - AQA Combined Higher Level
Faye Findlay
@fayefindlay_ylvf
1 / 5
Energy Changes in Chemical Reactions
Ever wondered why hand warmers heat up or why injury packs get cold? It's all about energy transfer during chemical reactions. When reactions happen, energy either gets released or absorbed.
Exothermic reactions give out heat energy to their surroundings, causing temperatures to rise. You'll see this in combustion (like burning fuel), neutralisation reactions, hand warmers, and self-heating cans. The key thing to remember: exothermic means energy exits the system.
Endothermic reactions take in heat energy from their surroundings, making temperatures drop. Think thermal decomposition, sports injury packs, and cooling systems. Here's where bond energies become crucial - breaking bonds always requires energy (endothermic), whilst forming bonds releases energy (exothermic).
Remember: Bond breaking = endothermic , Bond forming = exothermic
Acids, Bases and Chemical Changes
The pH scale might look complicated, but it's actually dead simple. Lower pH means more acidic, higher pH means more alkaline, and pH 7 is neutral - like pure water.
Strong acids completely break apart (ionise) in water, releasing loads of H+ ions. Weak acids only partially ionise, creating a reversible reaction. When acids meet bases, you get neutralisation: acid + base → salt + water.
Redox reactions involve the transfer of electrons. Oxidation means gaining oxygen, whilst reduction means losing it. The reactivity series ranks metals from most reactive (sodium) to least reactive (gold). In electrolysis, reduction happens at the negative electrode (cathode) where metals form, and oxidation occurs at the positive electrode (anode) where non-metals form.
Key Pattern: Acid + metal oxide/carbonate/metal = salt + water
Quantitative Chemistry and Calculations
Chemistry isn't just about reactions - it's about precise measurements and calculations that help predict what happens when chemicals react.
Relative formula mass (Mr) is simply adding up all the atomic masses in a compound's formula. Percentage mass tells you what fraction of a compound is made up of a particular element - use the formula: × 100.
A mole represents 6.02 × 10²³ particles (Avogadro's number) - it's chemistry's way of counting atoms and molecules. Concentration measures how much substance is dissolved in a given volume: concentration = mass ÷ volume.
Conservation of mass means atoms can't disappear - the total mass before a reaction equals the total mass after. Limiting reactants determine when reactions stop - once one chemical runs out, the reaction can't continue, leaving the other chemical in excess.
Pro Tip: In exam calculations, always show your working and include units - even if your final answer is wrong, you can still pick up marks!
Chemical Bonding and Structure
Understanding how atoms stick together explains why materials behave so differently. There are three main types of chemical bonding, each creating substances with unique properties.
Ionic bonding happens between metals and non-metals. Metals lose electrons to become positive ions, whilst non-metals gain electrons to become negative ions. These oppositely charged ions attract each other, forming giant ionic lattices with high melting points that don't conduct electricity when solid.
Covalent bonding occurs between non-metals that share electron pairs to get full outer shells. Simple covalent compounds exist as separate molecules, but giant covalent structures like diamond and graphite have atoms bonded throughout the entire structure with strong covalent bonds.
Metallic bonding involves delocalised electrons that move freely between metal atoms, explaining why metals conduct electricity and can form alloys.
State Changes: Solids have fixed positions (just vibrate), liquids move freely, and gases move randomly at high speed.
Atomic Structure and the Periodic Table
Atoms contain three tiny particles: protons , neutrons (no charge), and electrons . This simple structure explains how the entire periodic table works.
Metals are typically strong, conduct electricity, have high melting points, and get more reactive as you go down Group 1. Non-metals are often dull, don't conduct electricity, have lower melting points, and in Group 7 become less reactive going down.
The periodic table has evolved significantly. Early versions arranged elements by atomic weight, but Mendeleev cleverly left gaps for undiscovered elements. Today's table arranges elements by increasing atomic number (number of protons).
Separation techniques help us study pure substances: chromatography separates mixtures, evaporation removes solvents, crystallisation forms pure crystals, and distillation separates liquids. Remember that compounds have elements chemically bonded, whilst mixtures just have elements mixed together physically.
Historical Timeline: Dalton's sphere → Thomson's plum pudding → Rutherford's nuclear model → Bohr's electron shells → Modern quantum model
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.
Most popular content in Chemistry
Most popular content
Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5
App Store
4.7/5
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 Knowunity AI. 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 Knowunity AI. 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
GCSE Chemistry Paper 1 - AQA Combined Higher Level
Faye Findlay
@fayefindlay_ylvf
Chemistry can seem overwhelming at first, but these fundamental concepts are actually quite straightforward once you break them down. This guide covers the essential topics you'll need to master for your GCSE Chemistry exams, from energy changes in reactions to... Show more
Energy Changes in Chemical Reactions
Ever wondered why hand warmers heat up or why injury packs get cold? It's all about energy transfer during chemical reactions. When reactions happen, energy either gets released or absorbed.
Exothermic reactions give out heat energy to their surroundings, causing temperatures to rise. You'll see this in combustion (like burning fuel), neutralisation reactions, hand warmers, and self-heating cans. The key thing to remember: exothermic means energy exits the system.
Endothermic reactions take in heat energy from their surroundings, making temperatures drop. Think thermal decomposition, sports injury packs, and cooling systems. Here's where bond energies become crucial - breaking bonds always requires energy (endothermic), whilst forming bonds releases energy (exothermic).
Remember: Bond breaking = endothermic , Bond forming = exothermic
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Acids, Bases and Chemical Changes
The pH scale might look complicated, but it's actually dead simple. Lower pH means more acidic, higher pH means more alkaline, and pH 7 is neutral - like pure water.
Strong acids completely break apart (ionise) in water, releasing loads of H+ ions. Weak acids only partially ionise, creating a reversible reaction. When acids meet bases, you get neutralisation: acid + base → salt + water.
Redox reactions involve the transfer of electrons. Oxidation means gaining oxygen, whilst reduction means losing it. The reactivity series ranks metals from most reactive (sodium) to least reactive (gold). In electrolysis, reduction happens at the negative electrode (cathode) where metals form, and oxidation occurs at the positive electrode (anode) where non-metals form.
Key Pattern: Acid + metal oxide/carbonate/metal = salt + water
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Quantitative Chemistry and Calculations
Chemistry isn't just about reactions - it's about precise measurements and calculations that help predict what happens when chemicals react.
Relative formula mass (Mr) is simply adding up all the atomic masses in a compound's formula. Percentage mass tells you what fraction of a compound is made up of a particular element - use the formula: × 100.
A mole represents 6.02 × 10²³ particles (Avogadro's number) - it's chemistry's way of counting atoms and molecules. Concentration measures how much substance is dissolved in a given volume: concentration = mass ÷ volume.
Conservation of mass means atoms can't disappear - the total mass before a reaction equals the total mass after. Limiting reactants determine when reactions stop - once one chemical runs out, the reaction can't continue, leaving the other chemical in excess.
Pro Tip: In exam calculations, always show your working and include units - even if your final answer is wrong, you can still pick up marks!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Chemical Bonding and Structure
Understanding how atoms stick together explains why materials behave so differently. There are three main types of chemical bonding, each creating substances with unique properties.
Ionic bonding happens between metals and non-metals. Metals lose electrons to become positive ions, whilst non-metals gain electrons to become negative ions. These oppositely charged ions attract each other, forming giant ionic lattices with high melting points that don't conduct electricity when solid.
Covalent bonding occurs between non-metals that share electron pairs to get full outer shells. Simple covalent compounds exist as separate molecules, but giant covalent structures like diamond and graphite have atoms bonded throughout the entire structure with strong covalent bonds.
Metallic bonding involves delocalised electrons that move freely between metal atoms, explaining why metals conduct electricity and can form alloys.
State Changes: Solids have fixed positions (just vibrate), liquids move freely, and gases move randomly at high speed.
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Atomic Structure and the Periodic Table
Atoms contain three tiny particles: protons , neutrons (no charge), and electrons . This simple structure explains how the entire periodic table works.
Metals are typically strong, conduct electricity, have high melting points, and get more reactive as you go down Group 1. Non-metals are often dull, don't conduct electricity, have lower melting points, and in Group 7 become less reactive going down.
The periodic table has evolved significantly. Early versions arranged elements by atomic weight, but Mendeleev cleverly left gaps for undiscovered elements. Today's table arranges elements by increasing atomic number (number of protons).
Separation techniques help us study pure substances: chromatography separates mixtures, evaporation removes solvents, crystallisation forms pure crystals, and distillation separates liquids. Remember that compounds have elements chemically bonded, whilst mixtures just have elements mixed together physically.
Historical Timeline: Dalton's sphere → Thomson's plum pudding → Rutherford's nuclear model → Bohr's electron shells → Modern quantum model
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.
11
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Mock Exam
Quiz
Flashcards
Essay
Most popular content in Chemistry
Most popular content
Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5
App Store
4.7/5
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 Knowunity AI. 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 Knowunity AI. 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