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Organisms respond to changes in their internal and external environments (a-level only)
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Britain & the wider world: 1745 -1901
1l the quest for political stability: germany, 1871-1991
The cold war
Inter-war germany
Medieval period: 1066 -1509
2d religious conflict and the church in england, c1529-c1570
2o democracy and nazism: germany, 1918-1945
1f industrialisation and the people: britain, c1783-1885
1c the tudors: england, 1485-1603
2m wars and welfare: britain in transition, 1906-1957
World war two & the holocaust
2n revolution and dictatorship: russia, 1917-1953
2s the making of modern britain, 1951-2007
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Chemistry
9 Dec 2025
152
2 pages
Ella Battersby @ellabattersby_dprh
Chemical reactions and structures are all about energy and how atoms stick together. Understanding whether reactions give out... Show more
Ever wondered why some reactions feel hot whilst others feel cold? It's all about whether energy is being released or absorbed during the process.
Exothermic reactions are the ones that give out energy to their surroundings - think of burning wood or hand warmers. These happen because making new bonds between atoms releases energy. You'll spot these reactions because they warm up their surroundings.
Endothermic reactions do the opposite - they absorb energy from around them, making things feel colder. This happens because breaking bonds between atoms requires energy input. Ice packs use endothermic reactions to cool injuries.
Remember Bond making = energy out (exothermic), Bond breaking = energy in (endothermic)
These massive molecular structures explain why diamonds are so incredibly hard and why graphite makes excellent pencil lead. Giant covalent structures are built from huge numbers of non-metal atoms all connected by strong covalent bonds in regular, repeating patterns.
The main examples you'll encounter are diamond, graphite, and silicon dioxide. Because breaking all those strong covalent bonds requires loads of energy, these materials have very high melting and boiling points.
Most giant covalent structures don't conduct electricity because they lack charged particles. However, graphite is the fascinating exception to this rule.
Allotropes are simply different structural forms of the same element - like how diamond and graphite are both pure carbon but arranged completely differently.
Carbon shows off by forming two completely different structures with opposite properties. Understanding these helps explain why the same element can be both the hardest natural substance and a soft writing material.
Diamond has each carbon atom bonded to four others in a rigid 3D network. This creates an incredibly strong structure with a very high melting point. Since all electrons are locked in bonds, diamond can't conduct electricity - making it an excellent insulator.
Graphite takes a different approach, with each carbon bonded to only three others, forming layers. These layers have weak forces between them, so they slide over each other easily - perfect for pencils! The spare electron from each carbon can move freely, allowing graphite to conduct electricity and heat.
Key difference Diamond = 4 bonds per carbon (insulator), Graphite = 3 bonds per carbon (conductor)
Ionic bonding happens when metals meet non-metals and electrons get transferred from one to the other. Common examples include sodium chloride (table salt) and magnesium oxide.
Metals always lose electrons to become positive cations, whilst non-metals gain these electrons to become negative anions. This creates oppositely charged ions that attract each other strongly.
These ions arrange themselves in regular 3D lattices held together by strong electrostatic forces. This gives ionic compounds high melting and boiling points. Solid ionic compounds can't conduct electricity because the ions are fixed in place, but they conduct when molten or aqueous (dissolved in water) because the ions can move freely.
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.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
2
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the fundamentals of energy changes in chemical reactions, including exothermic and endothermic processes, bond energies, and practical applications like fuel cells and electrochemical cells. This summary is ideal for AQA GCSE students preparing for exams, featuring key concepts and practical insights to enhance understanding.
ChemistryExplore the principles of energy changes in chemical reactions, focusing on exothermic and endothermic processes, bond energy, and calorimetry techniques. This summary covers key concepts such as activation energy, collision theory, and the functioning of fuel cells and batteries. Ideal for GCSE Chemistry students preparing for AQA Higher Triple exams.
ChemistryExplore the principles of reversible reactions and dynamic equilibrium in AQA Chemistry. This summary covers Le Chatelier's principle, the effects of concentration, temperature, and pressure changes on equilibrium, and the characteristics of exothermic and endothermic reactions. Ideal for students preparing for exams.
ChemistryExplore the Haber Process for ammonia synthesis, its exothermic nature, and the production of NPK fertilizers. This summary covers key concepts including catalysts, nitrogen sources, and the differences between school lab and industrial processes. Ideal for GCSE Chemistry students.
ChemistryExplore the principles of chemical equilibrium, including Le Chatelier's Principle, factors affecting reaction rates, and the impact of concentration and pressure changes. This summary provides a clear overview of how systems respond to changes, ideal for GCSE Chemistry students preparing for exams.
ChemistryExplore the concepts of exothermic and endothermic reactions, including activation energy and energy transfer. This summary covers key definitions, energy profiles, and real-world examples such as combustion and thermal decomposition. Ideal for GCSE Chemistry students preparing for exams.
ChemistryApp Store
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
Ella Battersby
@ellabattersby_dprh
Chemical reactions and structures are all about energy and how atoms stick together. Understanding whether reactions give out or absorb energy, plus how different materials are built, will help you predict their properties and behaviour.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Ever wondered why some reactions feel hot whilst others feel cold? It's all about whether energy is being released or absorbed during the process.
Exothermic reactions are the ones that give out energy to their surroundings - think of burning wood or hand warmers. These happen because making new bonds between atoms releases energy. You'll spot these reactions because they warm up their surroundings.
Endothermic reactions do the opposite - they absorb energy from around them, making things feel colder. This happens because breaking bonds between atoms requires energy input. Ice packs use endothermic reactions to cool injuries.
Remember: Bond making = energy out (exothermic), Bond breaking = energy in (endothermic)
These massive molecular structures explain why diamonds are so incredibly hard and why graphite makes excellent pencil lead. Giant covalent structures are built from huge numbers of non-metal atoms all connected by strong covalent bonds in regular, repeating patterns.
The main examples you'll encounter are diamond, graphite, and silicon dioxide. Because breaking all those strong covalent bonds requires loads of energy, these materials have very high melting and boiling points.
Most giant covalent structures don't conduct electricity because they lack charged particles. However, graphite is the fascinating exception to this rule.
Allotropes are simply different structural forms of the same element - like how diamond and graphite are both pure carbon but arranged completely differently.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Carbon shows off by forming two completely different structures with opposite properties. Understanding these helps explain why the same element can be both the hardest natural substance and a soft writing material.
Diamond has each carbon atom bonded to four others in a rigid 3D network. This creates an incredibly strong structure with a very high melting point. Since all electrons are locked in bonds, diamond can't conduct electricity - making it an excellent insulator.
Graphite takes a different approach, with each carbon bonded to only three others, forming layers. These layers have weak forces between them, so they slide over each other easily - perfect for pencils! The spare electron from each carbon can move freely, allowing graphite to conduct electricity and heat.
Key difference: Diamond = 4 bonds per carbon (insulator), Graphite = 3 bonds per carbon (conductor)
Ionic bonding happens when metals meet non-metals and electrons get transferred from one to the other. Common examples include sodium chloride (table salt) and magnesium oxide.
Metals always lose electrons to become positive cations, whilst non-metals gain these electrons to become negative anions. This creates oppositely charged ions that attract each other strongly.
These ions arrange themselves in regular 3D lattices held together by strong electrostatic forces. This gives ionic compounds high melting and boiling points. Solid ionic compounds can't conduct electricity because the ions are fixed in place, but they conduct when molten or aqueous (dissolved in water) because the ions can move freely.
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.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
2
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore the fundamentals of energy changes in chemical reactions, including exothermic and endothermic processes, bond energies, and practical applications like fuel cells and electrochemical cells. This summary is ideal for AQA GCSE students preparing for exams, featuring key concepts and practical insights to enhance understanding.
ChemistryExplore the principles of energy changes in chemical reactions, focusing on exothermic and endothermic processes, bond energy, and calorimetry techniques. This summary covers key concepts such as activation energy, collision theory, and the functioning of fuel cells and batteries. Ideal for GCSE Chemistry students preparing for AQA Higher Triple exams.
ChemistryExplore the principles of reversible reactions and dynamic equilibrium in AQA Chemistry. This summary covers Le Chatelier's principle, the effects of concentration, temperature, and pressure changes on equilibrium, and the characteristics of exothermic and endothermic reactions. Ideal for students preparing for exams.
ChemistryExplore the Haber Process for ammonia synthesis, its exothermic nature, and the production of NPK fertilizers. This summary covers key concepts including catalysts, nitrogen sources, and the differences between school lab and industrial processes. Ideal for GCSE Chemistry students.
ChemistryExplore the principles of chemical equilibrium, including Le Chatelier's Principle, factors affecting reaction rates, and the impact of concentration and pressure changes. This summary provides a clear overview of how systems respond to changes, ideal for GCSE Chemistry students preparing for exams.
ChemistryExplore the concepts of exothermic and endothermic reactions, including activation energy and energy transfer. This summary covers key definitions, energy profiles, and real-world examples such as combustion and thermal decomposition. Ideal for GCSE Chemistry students preparing for exams.
ChemistryApp Store
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
Sociology