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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
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Chemistry
15 Dec 2025
521
2 pages
Organic chemistry might sound scary, but it's actually all about understanding the carbon-based compounds that power our world!... Show more
Ever wondered what's actually in crude oil? It's packed with hydrocarbons - molecules made only of hydrogen and carbon atoms. Think of them as nature's building blocks that took millions of years to form underground.
The most common hydrocarbons in crude oil are called alkanes. These molecules are like a family - they all follow the same pattern but come in different sizes. The general formula is C_nH_{2n+2}, which basically means for every carbon atom, you get roughly two hydrogen atoms plus a bit extra.
Alkanes are saturated hydrocarbons, meaning all their bonds are full up - they can't grab onto any more atoms. The first four you need to know are methane, ethane, propane, and butane. Here's a handy trick "mice eat paper bags" helps you remember the order!
Quick Tip The longer the carbon chain, the higher the boiling point. Short chains = runny liquids, long chains = thick, gooey substances.
Crude oil straight from the ground is pretty useless - it's like having a massive mixed-up toolbox. Fractional distillation is how we sort it into useful bits, and it's simpler than it sounds.
Picture a tall tower that's scorching hot at the bottom and cooler at the top. When crude oil gets heated up, different molecules rise to different levels based on their size. Short-chain hydrocarbons float to the top because they're held together weakly and boil easily.
Long-chain hydrocarbons stay near the bottom because they're tough cookies - their strong bonds mean they need serious heat to turn into gas. Each level collects molecules of similar sizes, creating different "fractions" we can use for petrol, diesel, or heating oil.
Sometimes we've got loads of long, boring hydrocarbon chains but need shorter, more exciting ones. Cracking is basically chemistry's way of chopping them up! It's a thermal decomposition reaction that breaks big molecules into smaller, more useful pieces.
There are two main ways to crack hydrocarbons using a catalyst (catalytic cracking) or steam (steam cracking). When you crack a long alkane, you get a shorter alkane plus something called an alkene.
Alkenes are the rebellious cousins of alkanes - they have a double bond that makes them unsaturated. Their general formula is C_nH_{2n}. This double bond is like a weak spot that can break open, letting other atoms join in.
Lab Test Drop bromine water on an alkane and it stays orange. Drop it on an alkene and it goes clear - the double bond grabs the bromine!
Here's where chemistry gets properly useful for your everyday life! Those alkenes from cracking don't just sit around - they link up to form polymers, which are basically very long chains of repeating units.
Poly(ethene) comes from ethene molecules joining hands to make plastic bags, bottles, and bins. Poly(propene) is made from propene and creates those tough, strong plastics you see everywhere.
Think of it like a paper chain you might make in primary school - each alkene is a paper loop, and when you connect loads together, you get a long, useful chain. The properties change too short chains flow easily, but long chains become thick and viscous.
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.
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Explore the structure and significance of the Periodic Table in this informative presentation. Learn about groups, periods, atomic numbers, and the classification of elements including metals, nonmetals, and noble gases. Ideal for students seeking to grasp the fundamentals of chemistry and periodic trends.
ChemistrySummary of the topic and key terms
ChemistryQuotes from every main character
English LiteratureApp 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 itโs 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 didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm 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 ๐๐๐ฒ๐ค๐โจ๐๐ฎ
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 itโs 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 didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm 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 ๐๐๐ฒ๐ค๐โจ๐๐ฎ
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
Organic chemistry might sound scary, but it's actually all about understanding the carbon-based compounds that power our world! From the petrol in cars to the plastic in your water bottle, these molecules are everywhere around you.
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Ever wondered what's actually in crude oil? It's packed with hydrocarbons - molecules made only of hydrogen and carbon atoms. Think of them as nature's building blocks that took millions of years to form underground.
The most common hydrocarbons in crude oil are called alkanes. These molecules are like a family - they all follow the same pattern but come in different sizes. The general formula is C_nH_{2n+2}, which basically means for every carbon atom, you get roughly two hydrogen atoms plus a bit extra.
Alkanes are saturated hydrocarbons, meaning all their bonds are full up - they can't grab onto any more atoms. The first four you need to know are methane, ethane, propane, and butane. Here's a handy trick: "mice eat paper bags" helps you remember the order!
Quick Tip: The longer the carbon chain, the higher the boiling point. Short chains = runny liquids, long chains = thick, gooey substances.
Crude oil straight from the ground is pretty useless - it's like having a massive mixed-up toolbox. Fractional distillation is how we sort it into useful bits, and it's simpler than it sounds.
Picture a tall tower that's scorching hot at the bottom and cooler at the top. When crude oil gets heated up, different molecules rise to different levels based on their size. Short-chain hydrocarbons float to the top because they're held together weakly and boil easily.
Long-chain hydrocarbons stay near the bottom because they're tough cookies - their strong bonds mean they need serious heat to turn into gas. Each level collects molecules of similar sizes, creating different "fractions" we can use for petrol, diesel, or heating oil.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Sometimes we've got loads of long, boring hydrocarbon chains but need shorter, more exciting ones. Cracking is basically chemistry's way of chopping them up! It's a thermal decomposition reaction that breaks big molecules into smaller, more useful pieces.
There are two main ways to crack hydrocarbons: using a catalyst (catalytic cracking) or steam (steam cracking). When you crack a long alkane, you get a shorter alkane plus something called an alkene.
Alkenes are the rebellious cousins of alkanes - they have a double bond that makes them unsaturated. Their general formula is C_nH_{2n}. This double bond is like a weak spot that can break open, letting other atoms join in.
Lab Test: Drop bromine water on an alkane and it stays orange. Drop it on an alkene and it goes clear - the double bond grabs the bromine!
Here's where chemistry gets properly useful for your everyday life! Those alkenes from cracking don't just sit around - they link up to form polymers, which are basically very long chains of repeating units.
Poly(ethene) comes from ethene molecules joining hands to make plastic bags, bottles, and bins. Poly(propene) is made from propene and creates those tough, strong plastics you see everywhere.
Think of it like a paper chain you might make in primary school - each alkene is a paper loop, and when you connect loads together, you get a long, useful chain. The properties change too: short chains flow easily, but long chains become thick and viscous.
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 โ all at your fingertips.
5
Smart Tools NEW
Transform this note into: โ 50+ Practice Questions โ Interactive Flashcards โ Full Mock Exam โ Essay Outlines
Explore the structure and significance of the Periodic Table in this informative presentation. Learn about groups, periods, atomic numbers, and the classification of elements including metals, nonmetals, and noble gases. Ideal for students seeking to grasp the fundamentals of chemistry and periodic trends.
ChemistrySummary of the topic and key terms
ChemistryQuotes from every main character
English LiteratureApp 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 itโs 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 didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm 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 ๐๐๐ฒ๐ค๐โจ๐๐ฎ
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 itโs 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 didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm 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 ๐๐๐ฒ๐ค๐โจ๐๐ฎ
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