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6 Dec 2025
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GCSE Chemistry Energy Changes - Active Recall for AQA Triple
Zainab
@zainab_02839
1 / 5
Exothermic and Endothermic Reactions
Every chemical reaction either gives out energy or takes it in - there's no middle ground! Exothermic reactions transfer energy to their surroundings, making things feel warmer. Think of striking a match or adding acid to an alkali - the temperature rises because energy is being released.
Endothermic reactions do the opposite by absorbing energy from their surroundings, making things feel colder. When you mix citric acid with sodium hydrogencarbonate (like in sherbet), the mixture gets noticeably cooler.
The key is all about bond energy. In exothermic reactions, more energy is released when new bonds form than was needed to break the original bonds. For endothermic reactions, breaking the original bonds requires more energy than you get back from forming new ones.
Remember: Exothermic = Exit (energy leaves), Endothermic = Enter (energy enters)
Measuring Temperature Changes and Collision Theory
You can easily measure energy changes in neutralisation reactions using simple lab equipment. Start with 30cm³ of acid, record its temperature, then gradually add 5cm³ portions of alkali whilst stirring and recording the highest temperature reached each time.
Chemical reactions only happen when particles actually crash into each other - this is collision theory. But not every collision works! Particles need enough energy to overcome the activation energy barrier, which is like the minimum entrance fee for a reaction to occur.
Reaction profiles are brilliant graphs that show this energy journey. For exothermic reactions, the products end up at a lower energy level than the reactants (energy has been released). Endothermic reactions show the opposite pattern.
Top tip: The activation energy is always the peak of the energy curve, regardless of whether the reaction is exothermic or endothermic.
Bond Energy Calculations
Bond energy is the amount of energy needed to break one mole of a specific bond - think of it as the 'breaking fee' for chemical bonds. This concept helps you calculate exactly how much energy a reaction will release or absorb.
To work out the overall energy change, use this simple formula: energy needed to break reactant bonds minus energy released from forming product bonds. If your answer is positive, the reaction is endothermic; if negative, it's exothermic.
Remember that breaking bonds always requires energy (endothermic process) whilst forming bonds always releases energy (exothermic process). The overall reaction type depends on which process needs more energy.
Quick check: If more energy goes into breaking bonds than comes out from forming new ones, the reaction feels cold (endothermic).
Chemical Cells and Fuel Cells
A simple cell is just two different metals connected through an electrolyte solution - it's like a basic battery you could make at home! When you connect multiple cells in series, you get a battery with higher voltage.
Some batteries are rechargeable because you can reverse their chemical reactions by applying external electricity. Others, like alkaline batteries, are non-rechargeable because their reactants get completely used up and can't be restored.
Fuel cells work differently - they're like batteries that never run out as long as you keep feeding them fuel. In a hydrogen fuel cell, hydrogen loses electrons at the negative electrode whilst oxygen gains electrons at the positive electrode, producing electricity and water.
Cool fact: The overall reaction in a hydrogen fuel cell is just making water whilst generating electricity!
Fuel Cells vs Rechargeable Batteries
Hydrogen fuel cells have some brilliant advantages over traditional batteries. They keep working efficiently as long as you supply hydrogen, whilst rechargeable batteries gradually lose their storage capacity and eventually need replacing completely.
Fuel cells even produce drinking water as a bonus! However, storing hydrogen safely is tricky because it's explosive, whereas most batteries use safer materials (though some can catch fire if poorly made).
The main drawback of fuel cells is their low potential difference, meaning you need several connected together to get useful voltage. Regular batteries pack more electrical punch in a smaller package, making them better for portable devices.
Environmental win: Fuel cells only produce water as waste, making them much cleaner than fossil fuel alternatives.
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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
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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
GCSE Chemistry Energy Changes - Active Recall for AQA Triple
Zainab
@zainab_02839
Energy changes are everywhere in chemistry - from the heat you feel when burning fuel to the cold sensation of ice melting. Understanding whether reactions release or absorb energy is crucial for predicting how chemicals behave and designing everything from... Show more
Exothermic and Endothermic Reactions
Every chemical reaction either gives out energy or takes it in - there's no middle ground! Exothermic reactions transfer energy to their surroundings, making things feel warmer. Think of striking a match or adding acid to an alkali - the temperature rises because energy is being released.
Endothermic reactions do the opposite by absorbing energy from their surroundings, making things feel colder. When you mix citric acid with sodium hydrogencarbonate (like in sherbet), the mixture gets noticeably cooler.
The key is all about bond energy. In exothermic reactions, more energy is released when new bonds form than was needed to break the original bonds. For endothermic reactions, breaking the original bonds requires more energy than you get back from forming new ones.
Remember: Exothermic = Exit (energy leaves), Endothermic = Enter (energy enters)
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Measuring Temperature Changes and Collision Theory
You can easily measure energy changes in neutralisation reactions using simple lab equipment. Start with 30cm³ of acid, record its temperature, then gradually add 5cm³ portions of alkali whilst stirring and recording the highest temperature reached each time.
Chemical reactions only happen when particles actually crash into each other - this is collision theory. But not every collision works! Particles need enough energy to overcome the activation energy barrier, which is like the minimum entrance fee for a reaction to occur.
Reaction profiles are brilliant graphs that show this energy journey. For exothermic reactions, the products end up at a lower energy level than the reactants (energy has been released). Endothermic reactions show the opposite pattern.
Top tip: The activation energy is always the peak of the energy curve, regardless of whether the reaction is exothermic or endothermic.
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Bond Energy Calculations
Bond energy is the amount of energy needed to break one mole of a specific bond - think of it as the 'breaking fee' for chemical bonds. This concept helps you calculate exactly how much energy a reaction will release or absorb.
To work out the overall energy change, use this simple formula: energy needed to break reactant bonds minus energy released from forming product bonds. If your answer is positive, the reaction is endothermic; if negative, it's exothermic.
Remember that breaking bonds always requires energy (endothermic process) whilst forming bonds always releases energy (exothermic process). The overall reaction type depends on which process needs more energy.
Quick check: If more energy goes into breaking bonds than comes out from forming new ones, the reaction feels cold (endothermic).
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Chemical Cells and Fuel Cells
A simple cell is just two different metals connected through an electrolyte solution - it's like a basic battery you could make at home! When you connect multiple cells in series, you get a battery with higher voltage.
Some batteries are rechargeable because you can reverse their chemical reactions by applying external electricity. Others, like alkaline batteries, are non-rechargeable because their reactants get completely used up and can't be restored.
Fuel cells work differently - they're like batteries that never run out as long as you keep feeding them fuel. In a hydrogen fuel cell, hydrogen loses electrons at the negative electrode whilst oxygen gains electrons at the positive electrode, producing electricity and water.
Cool fact: The overall reaction in a hydrogen fuel cell is just making water whilst generating electricity!
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By signing up you accept Terms of Service and Privacy Policy
Fuel Cells vs Rechargeable Batteries
Hydrogen fuel cells have some brilliant advantages over traditional batteries. They keep working efficiently as long as you supply hydrogen, whilst rechargeable batteries gradually lose their storage capacity and eventually need replacing completely.
Fuel cells even produce drinking water as a bonus! However, storing hydrogen safely is tricky because it's explosive, whereas most batteries use safer materials (though some can catch fire if poorly made).
The main drawback of fuel cells is their low potential difference, meaning you need several connected together to get useful voltage. Regular batteries pack more electrical punch in a smaller package, making them better for portable devices.
Environmental win: Fuel cells only produce water as waste, making them much cleaner than fossil fuel alternatives.
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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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